THE EFFECT OF FOURTH COMPONENT ADDITIONS, IRON AND (CHROMIUM, ON THE MAGNETIC PROPERTIES OF MB3AIC by F R A N K S T U A R T D E A T H A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE in the Department of MINING AND METALLURGY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE ° Members of the Department of Mining and Metallurgy» THE UNIVERSITY OF BRITISH COLUMBIA. October, 1956. ABSTRACT Previous work had shown that near the composition MneoAl2oC2o there occurs a highly ordered cubic phase with interesting magnetic properties. A study of the effect of additions of iron and chromium has been carried out with a view to obtaining some information about the structure and magnetic properties. Two alloy groups were studied, f i r s t , Mn6o(Fe °r C r ) x Al2o-xc2o and second Mneo»x( P e o r cr)x A 120 c20« It was found that i n the former group the magnetization decreased markedly with either Fe or Cr additions. The results could be represented by assuming the manganese moments were constant and the Fe or Cr atoms had a net moment of -5 Bohr magnetons when replacing an Aluminum atom. The second group yielded no such simple representation because the moment per magnetic atom values varied quite irregularly. The only possible observation was that the average moment was always less than that of manganese i n M113AIC. ACKNOWLEDGEMENT The author i s grateful for financial aid i n the form of a National Research Council Bursary during the summers of 1955 and 1956, and the university year 1955'* "56. The work was done with the help of funds provided by the Defence Research Board under Research Grant 28l. The experimental work was done in the laboratories of the Department of Mining and Metallurgy, and the author i s grateful for the assistance offered and the f a c i l i t i e s available to him. Special thanks are extended to;Dr. H.P. Myers, the director of this research, and R.G. Butters for technical advice and encouragement. TABLE OF CONTENTS Page I. INTRODUCTION . . . . . . . . . . . . . . . . . o . . o o o, « « o 1 I I . PREVIOUS WORK 1 o Mn^Zn^C systGin OOOOOOOOOOOOOOOOGOOOO 3 2o Mn^Al^C systsni OOOOOOOOOOOOODOOOOOOO 5 H I . EXPERIMENTAL PROCEDURE" 1. Preparation of the Alloys . . . . . . . a . . . . . . . 7 2. Heat Treatments . . . a o . o a o . o . . o o o . o o o 7 3. Metallography ....................D 8 ha Structure and Lattice Parameter Measurements „ . <> . . 8 5« Magnetic Measurements „ . . . » . . . . . . . . . . . . 11 6o Thermal Expansion Measurements „ „ o . . . ° . . . . . o 13 IV. RESULTS 1. Metallography . . . . . . . . . . . . . . . . . . . . . I k .2. Structure and Lattice Parameter Measurements . . . . . . l8 3» Magnetic Measurements . . . . . . . . . . . . . . . a . 22 V. . DISCUSSION OF RESULTS AND CONCLUSIONS . . . . . . . . . . . . . 31 VX a APPENDIX O O O O O O O O O O O O O O O O O O O C 7 0 0 0 0 0 0 0 5^ VII o BIBLIOGRAPHY tto«oo*oooeooo»oeooOoooooo 5T ILLUSTRATIONS lo The proposed structure of MngAlC and Mn®5.nC OOO°POOOOOOOO k 2, A view of the ferromagnetic head of the Sucksraith ring balance a . <> ° 12 3° Microstructure of an alloy of nominal composition MnssFeaAlsoCao » » • 15 ho Microstructure of an alloy of nominal composition MnsTCz'sAlsoCgo • • « 15 5» The variation of lattice parameter with atomic percent iron or chromium in alloys of the form MnsoXxAlso^xCso » » ° <> ° ° ° ° ° ° » 1°" 6. The variation of lattice parameter with atomic percent iron in alloys of the form Mrieo^x^x^ 2 0^ 2 0 . < . o . » < . o o „ o < . o < . o o a 17 7- The variation of lattice parameter of M113AIC with temperature <> „ » 19 8. The variation of Curie temperature with atomic percent iron or chromium in alloys of the form MngoXxAlgo-xCao « a o o <, 0 o » o 23 9» The variation of Curie temperature with atomic percent iron in alloys of the form Mnso=»x^ 6x^^ 2 0^ 2 0 s o o . . . . . . . * . . . . . 2^ -10o The variation of saturation magnetization with temperature for three sample alloys of the form MneoFexAl2o„xC2Q . . <. <> » . » . » o 25 11. The variation of saturation magnetization with temperature for two sample alloys of the form MneOcoxFe^laoCao 0 0 0 < , „ 0 0 0 o o 0 26 12. The variation of Bohr magneton value per magnetic atom with atomic percent iron or chromium in alloys of the form 13o The variation of Bohr magneton value per magnetic atom with atomic percent iron i n alloys of the form Mnecu^Fe^laoCao o o o o o 28 TABLES 1. The measured and calculated x«ray line intensities for the alloy of nominal composition MnaoFegoAlsoCao o o o 0 0 0 0 o 0 o < > 20 2o The measured properties of a l l alloys o o » < , o o ° o a o o o o o 21 lo THE EFFECT OF FOURTH COMPONENT ADDITIONS, IRON AND CHROMIUM, ON THE MAGNETIC PROPERTIES OF MnjjAlC I. INTRODUCTION # , Interest In the effect of fourth component additions to the alloy MneoAlaoCao* arose from previous work done on this alloy and MnsoZn2oC2o° It has been shown that these two alloys have an iso-morphous structure and interesting but different magnetic properties. The structure i n both alloys is a highly ordered face-centered cubic structure with magnanese atoms at face-center sites, aluminum or zinc atoms at cube corner positions and carbon at the body center position. The results of magnetic, x-ray and neutron diffraction studies on an alloy close to the optimum composition MneoAlao^o shows the behaviour to be typically ferromagnetic rather than ferrimagnetlc. The isomorphous alloy MneoZri2oC2o o n the other hand shows unusual magnetic behaviour being ferromagnetic from =42°C to the Curie temperature at 8o*"C and having complex ferrimagnetlc properties below «=42°C (Butters and Myers 1955 h). It is of considerable interest therefore to gather data which may provide for a proper understanding of the unusual structure and magnetic behaviour of these alloys. It was f e l t that because of the extreme ordering It might be possible to specify which sites in the lattice addition atoms would occupy. Thus i f additions were made at the expense of a corner atom then i t was hoped that the addition ft A l l compositions referred to throughout are atomic percent. atoms would occupy cube corner positions. Iron and chromium were chosen as possible addition atoms because of their close similarity in size and electron structure to manganese. I f i t were possible to specify addition atom positions then i t was f e l t that the resulting data would be useful i n an interpretation of the magnetic behaviour of the iso= morphous alloys. It i s for this reason that an investigation of the manganese°iron-=aluminura=ca rbon and manganese =chromium^aluminum=carbon systems was started. Two groups of alloys were chosen for study. In the f i r s t group additions were made at the expense of aluminum in the hope that the Iron or chromium additions would occupy cube corner positions. The second group consisted of alloys with additions at the expense of manganese, this time with the hope that the addition atoms would occupy face center positions. I I . PREVIOUS WORK I t has been shown t h a t s e v e r a l t e r n a r y a l l o y s c o n t a i n i n g manganese and carbon are s i n g l e phase and e x h i b i t ferromagnet ism. Aluminum, z i n c , g a l l i u m and i r o n have been used s u c c e s s f u l l y as t h i r d c o n s t i t u e n t s . The magnetic p r o p e r t i e s o f those a l l o y s c o n t a i n i n g aluminum and z i n c have been i n v e s t i g a t e d by B u t t e r s and Myers (1955 a and b ) . F o r c o m p o s i t i o n s c l o s e t o MneoAlaoCao o r MneoZnaoOao* the a l l o y s have been found t o possess the h i g h l y ordered f a c e - c e n t e r e d c u b i c s t r u c t u r e shown i n f i g . 1. I t i s f e l t t h a t t h i s s t r u c t u r e i s not an o r d i n a r y s u p e r l a t t i c e as i t occurs i n d e p e n d e n t l y o f heat t r e a t -ment. E i t h e r i t i s not an o r d i n a r y s u p e r l a t t i c e o r the c r i t i c a l temperature f o r o r d e r i n g I s above the m e l t i n g p o i n t f o r the a l l o y . Mn~Zn»C System The c h a r a c t e r i s t i c f . c . c . phase i n the Mn=Zn-C system e x i s t s over the range o f c o m p o s i t i o n MneoZnaoCgo t o about MnyoZnioC2o» I n a l l work the carbon content was h e l d c o n s t a n t a t 20 atomic p e r c e n t . T h i s was necessary so t h a t a l l atoms o f one s p e c i e s would l i e i n e x a c t l y the same environment . I f the atomic percent C was p e r m i t t e d t o drop below 20 percent t h e n some u n i t cubes would not have carbon body c e n t e r s and thus the atoms c o u l d be expected t o have d i f f e r e n t magnetic p r o p e r t i e s I t was found t h a t a l l o y s c l o s e t o MaeoZnzoCzo possessed a second o r d e r t r a n s i t i o n a t =^2°C. From measurements o f i n t e n s i t i e s o f x - r a y l i n e components, i t was c a l c u l a t e d t h a t the s t r u c t u r e changed from the ordered c u b i c t o an ordered t e t r a g o n a l s t r u c t u r e . Measurements o f Figure 1 The Proposed Structure of Mri3AlC and MnaZnC (Butters and Myers 1955) saturation magnetization revealed a highly singular feature. Below ?42°C the saturation magnetization decreased with decreasing temperature. Neutron diffraction studies on the alloy Mne0«eZni9.iC2o showed that above the temperature °h2°C the substance was a normal ferromagnetic with a mean Bohr magneton number per manganese atom of 1.5* Below, this c r i t i c a l temperature a complex ordering of magnetic moments arises. As manganese is added at the expense of zinc i t was observed that the Bohr magneton value per atom dropped markedly. It was found that this drop could be represented by assuming the manganese atoms which occupy zinc cube corner sites had a moment of h Bohr magnetons aligned antiparallel to the face center manganese moments. .1. Mn-Al-C system The distinctive f.c.c. phase in the Mn-Al-C system occurred for manganese contents ranging from 60 to approximately 70 percent with the carbon content held constant at 20 percent. The fact that the lower limit for s t a b i l i t y was Mn = 60 percent was taken to imply that the aluminum atoms are unable to take up the face center sites. The extrapolated saturation moment at 0°K of an alloy Mn60'TAlie.eCi9«>T i s 99«6 ergs/g/oersted which i s equivalent to a Bohr magneton number of 1.20 per manganese atom. The Curie temperature was 15°C. X-ray, magnetic, and neutron diffraction experiments on the system showed the alloys to be ferromagnetic rather than ferrimag-netio as in the Mn-Zn-C system. By extrapolation the Bohr magneton number per manganese atom i n MneoAl2oC2o was taken to be 1 .23° As i n the zinc alloy system discussed previously, the saturation moment at 0°K dropped markedly for manganese compositions greater than 60 peroent. Again i t was found that this drop could be represented by assuming the face center manganese atoms had a constant moment of 1.23/ <£ , and the excess manganese atoms had a moment of k/fe aligned antiparallel to the former. I I I . EXPERIMENTAL PROCEDURE 1. Preparation of the Alloys The materials used in this work were manganese of 99 »9 percent purity donated by the Electromanganese Corporation of America, aluminum of 99»99 percent purity donated by the Aluminum Company of Canada, either iron of 99.8 percent purity donated by Plastic Metals Company or powdered pure iron, carbon free fused chromium, and graphite of spectroscopic grade. The alloys were prepared by high frequency induction heating in an argon atmosphere. Stoichiometric mixtures of a l l alloy components except aluminum were heated to red beat under vacuum i n a high grade alumina crucible to allow degassing to occur. After degassing the unit was flooded with purified argon to almost atmospheric pressure. The components contained i n the crucible were next melted after which the crucible was raised so that the aluminum constituent 9 suspended on a thread, was consumed by the melt. The alloy was heated well above the melting point to allow for good mixing and then c h i l i east into a s p l i t brass mould. No contaiminatlon of the alloy by the mould was apparent 2. Heat Treatments A l l alloys were sealed i n evacuated quartz tubes. A homogenization treatment of one, week at 1000°C was adopted followed by a furnace cool to room temperature. After the homogenization treatment two different heat treatments were employed. Coarse powder samples of each specimen contained in molybdenum boats were reheated to 1000°C in a small tube furnace. The samples were held in a purified argon atmosphere at 10O0°C for three minutes. The tube furnace was then evacuated and immediately reflooded with a blast of helium gas. The helium blast blew the sample out of the furnace tube into a collecting bottle and at the same time quickly quenched the powder to room temperature. Other lump samples of each specimen were resealed in evacuated quartz tubes and reheated to 1000°C in a three inch tube furnace. The furnace was then slowly cooled from 10Q0°C down to 500°C in a time of I 1 * days. The slow cooling was accomplished by means of a small motor slowly turning the powerstat governing the input power to the furnace. A linear decrease of temperature with time was obtained. 3» Metallography A l l homogenized samples were mounted in lucite, polished, etched and observed under the microscope. A k percent nital etch was used in a l l alloys containing iron and some containing chromium. In other chromium containing alloys i t was found necessary to used mixed acids in glycerol to reveal any second phase areas. k. Structure and Lattioe Parameter Measurements Lattice parameters were obtained by measurement of Debye-Soherrer powder photographs. Either iron or chromium Re* radiation was used. The alloys were very b r i t t l e so that powders were easily prepared. It was found unnecessary to anneal the powders i n order to get sharp diffraction lines. Structure determinations were carried out with a Geiger counter spectrometer. Line intensities were obtained by measurement of the line areas above the background level and these were compared with calculated values. In the calculations the temperature factor was omitted but the atomic scattering factor was corrected for any depression i n the region of the absorption edges (James, 19^8). The formula for relative intensities Is _£ Cxi — where G Is the angle of diffraction, P i s the multiplicity factor of families of planes, and (F) i s the geometrical factor. Calculations were carried out on two alternative models for the alloy Mn39.eFe2o»3Al2o«7Ci9»5 (approximately Mn4,oFe2oAl2oC2o) • In the f i r s t model i t was assumed that there was ordering of the iron and manganese atoms at face center positions. For purposes of c a l -culation i t was assumed that the one iron atom per c e l l was found at l/2, l/2, 0 and the two manganese atoms per c e l l occupied the positions l/2, 0, l/2 and 0, l/2, l/2. In the second model i t was assumed that no ordering of atoms took place at face center positions. In this case the atomic scatter?" .. ing factor of the atoms of face center sites, for the purpose of c a l -culations, was an average value, compounded of the atomic scattering factors of both iron and manganese. In the model based on preferred orientation of the iron and manganese atoms the geometrical factor occurring in the expression for the line intensities takes the values (fAl-fC-fpe) when %Jhd odd and ( fAl + fC + fFe~ 2 fMn) 2 w b e n e v e n for the superlattice lines. These lines are taken to be those with £ h 2 = 1,2,5,9. For the normal lines corresponding to the face centered cubic structure, that Is 2 k 2 = 3,^,8,11, the geometrical factor takes the values ( fAl- fC + fFe + 2 fMn) 2 f o r ^ o d d and ( f A l + f C + f F e + 2 W 2 f o r ^ b 2 e v e n where f.,, f„, f„ , f„. are the atomic scattering factors for Al* C - Fe' Mn aluminum, carbon, Iron, and magnanese respectively. In those calculations based on random orientation of iron and manganese atoms at face center positions the geometrical factor takes the values ( f A 1 - f c - f a v ) 2 when £ h 2 odd 2 2 and ( fAl + fC" fav) w h e n £ h e v e n for the superlattice lines with £ h 2 = 1,2,5,9. For the normal face center cubic lines, ^.h 2 = 3,^,8,11, the geometrical factor takes the values ( f A 1 = f c + 3 f a v ) 2 when X h 2 odd 2 ^"2 and ( fAl + fC +3 fav) w h e n e v e n where f a v - Xl'i^X-^^.fy^ and other terms are as defined previously. 5« Magnetic Measurements A Sucksmith ring balance ( f i g . 2) was used to obtain measure-ments of the variation of saturation magnetization with temperature» Small platinum carriers containing coarse powder specimens of approxi-mately 3 0 milligrams were placed in an external f i e l d of 16,200 oersteds» The electromagnet pole pieces are shaped so that a uniform f i e l d gradient Is produced over an appreciable region about the specimen. The force exerted on a specimen of mass m and magnetic moment per unit mass ^ , is given by The ring balance has a deflection proportional to the force exerted on a specimen. Thus we may compare the force exerted on a specimen of unkown saturation magnetization with the force exerted on a standard iron sample of known magnetization. This may be done without knowing the f i e l d gradient, thus where the subscript " s " refers to the specimen of unkown magnetization, the subscript " ' f e 8 ' refers to the standard iron sample, and d i s the deflection of the specimen i n the f i e l d gradient. Therefore we have 5 ' *k 1 2 . Figure 2 A view of the ferromagnetic head of the Sucksmith ring balance Measurements of saturation magnetization were made over the range of temperature from 117°K to the Curie temperature which i n a l l cases was below 6l5°K. Temperatures below room temperature were obtained by submerging the specimen i n liquid oxygen and then allowing the sample to warm slowly to room temperatureo Above room temperature a small chromel wound tube furnace assembly with f a c i l i t i e s for evacu-ating the volume around the specimen was used. Prom the variation of with temperature the saturation magnetization at absolute zero was obtained from an extrapolation to o°K of a versus T^ ploto The Curie temperature was obtained by extrapolating to <^ = 0 a plot 2 of against T. 6. Thermal Expansion Measurements Thermal expansion measurements were carried out on an alloy of composition Mneo°7Ali9°eCis»7» ^°e geiger counter spectrometer was used to follow the movement of line Z h ^ = 4 with temperature <> An attachment u t i l i z i n g a liquid oxygen boiler to obtain temperature variations was used below room temperature. Above room temperature a platinum wound furnace assembly was employed with a helium atmosphere surrounding the specimen. XV. RESULTS 1o Metallography In alloys of the form MneoPexAl2o<=x^2o i t was observed that the limits of the single phase of interest were x = 0 to 5 percent. Por chromium additions the upper limit was found to be 3 percent. Above these limits, second phase regions were apparent. A rather unusual situation was observed i n alloys i n which iron and chromium additions replaced manganese. For as l i t t l e as one percent addition of either iron or chromium a needle-like or blocky second phase was formed. This i s illustrated i n f i g . 3 and f i g . k showing the similarity of the second phases present i n alloys of com-position MnsgPe2Al2oC2o and Mn 57Cr3Al20C2o. For increasing amounts of iron and chromium the amount of second phase decreases u n t i l for iron at M> percent and chromium at 5 percent the original single phase ordered structure i s once more observed. No range of composition for chromium additions with preservation of the single phase was observed. The only single phase alloy observed was MnssCrsAlgoCgo. Iron addi-tions were found to maintain the single phase for a range of composi-tion from Fe at 10 to 20 percent. Attempts were made to eliminate the blocky second phase i n Mns7Cr3Al2oC2o• Samples were sealed into evacuated quartz tubes and homogenized for a further week at one of the following temperatures Figure 3 Alloy of nominal composition Mn 5 eFe 2Al2oC 2o Nital etch xlJOO Figure k Alloy of nominal composition Mn 5 7Cr3Al 2oC2o Nital etch xl300 Figure 5 The variation of lattice parameter, with atomic # iron or chromium In alloys of the form MneoXxAl2o-xC2o 17. Figure 6 The variation of lattice parameter with atomic # iron in alloys of the form VLneo-xfeyAXzoVzo 10Q0°C, 9G0°C, 700°,600°. Following these treatments the specimens were water quenched« No variation In amount of second phase present was observed. Similarly we attempted to eliminate the second phase i n alloys with iron contents less than 10 percent. Longer homogeniza-tion treatments at 1000°C followed by water quenching resulted in no reduction i n the amount of second phase present. 2. Structure and Lattice Parameter Measurements The variation of lattice parameter with the fourth component additions i s given i n figures 5 and 6. The parameter of MnaAlC is taken to be 3-869A°. Actually this i s the parameter of an alloy of composition Mneo«7AliS»eCi8<»T" The parameter of MnsAlC should more correctly be an extrapolation of the variation of parameter with percent manganese In the Mn-Al-C system, however the parameter changes very rapidly near 60 percent manganese and the extrapolation is quite uncertain. However i t can be stated that the parameter of MnaAlC w i l l be equal or less than 3.869°A. Thus It can be appreciated that the maximum i n the lattice parameter variation with percent iron (figure 5) is real and not simply due to errors i n film measurement. In alloys of the form MneoXxAlao^Czo there i s then a distinct increase i n parameter with small additions of either chromium or Iron. For iron contents larger than two percent the parameter decreases. The results of line Intensity measurements as well as calculated values for the two models based on the different types of order are given i n table 1. The measured values quoted are the average values of four separate measurements. Figure 7 The variation of lattice parameter of MnsAlC with temperature TABLE 1 Line Index Measured Intensity-Calculated 1 Calculated 1 22.1 17.2 15-2 2 not measurable 1.8 3 100.0 100.0 100*0 k 55.2 58.5 5806 5 3 8.1 •k.6 k.0 8 65-3 60.6 60*6 9 f> not measurable 3.0 3-9 The measured and calculated Intensities are based on a value 100 for the line £h 2 = 3 Specimen Composition M i i ^ s . 3 A I 2 0 »-fixs « 5 Lattice Parameter 3.837 A 0 1. Assumed preferred orientation of Fe and Mn at cube faces Fe =l/2, 1/2, 0 Mn = l/2, 0 , l/2 0,l/2,l/2 2. Assumed random distribution of Fe and Mn at cube faces. 21c TABLE 2 Composition Heat Curie Saturation Bohr Lattice Mn Pe Al Quenoh=Q« C Slow cool S.C. °c . 60.0 1.0 19.5 19.5 Q. S.C. iS 92.0 92.0 1.11 1.11 3.870 3.870 59.0 2.5 19-7 19.8 Q. 3«C • 143 147 88.5 86.9 l„06 1.04 3.870 3.870 58.7 3.2 17.9 20.2 Q. S «C • 207 197 72.1 73.1 .86 .87 3.870 3.869 59.0 4.2 16.3 20.6 Q. S »C 0 292 283 69.O 69*1 .81 .82 3.867 3.868 59.1 5.6 15.1 29.2 335 310 66.7 61.5 .78 .72 3.866 3.866 49.2 10.1 20.4 20.4 Q. 3 «C • 69 52 84.5 79.5 1.04 .98 3.857 3.858 48.1 12.6 20.1 19.3 Q. S 0 C 0 55 4i 92.1 92.4 1.12 1.12 3.853 3.853 44.8 15.3 20.9 19.1 Q . S aC » 53 45 92.0 88.9 1.13 1.09 3.847 3.848 43.2 16.5 20.7 19.6 S.C. 48 39 84.9 82.9 1.04 1.02 3.845 3.845 39.6 20.3 20.7 19.4 Q. S «C 0 39 35 90.7 88.6 1.11 1.09 3.837 3.837 Unassayed Alloys Furnace cooled 49 11 20 20 . » ? 49 89.6 1.09 3.854 46 14 20 20 45 91.1 1.11 3.850 42 18 20 20 < » 4l 85.O 1.04 3.844 Mn Cr Al C 60 1 19 20 » » 92 92.0 1.11 3.874 60 2 18 20 9 > 152 85.6 1.02 3.875 60 3 17 20 » « 210 73.2 .86 3.874 55 5 20 20 f J •=35 85.5 1.04 3.875 22. The variation of lattice parameter with temperature of Mnte»7Ali9°igCi9°7 is given in f i g . 7» Although the composition of the alloy i s not exactly MnsAlC the results are useful for a qualitative description of the variation of MnsAlC through the region of the Curie temperature. Magnetic Measurements The measured values i n a f i e l d of 16,200 oersted, of Curie temperature 6 ^ , and saturation magnetization at absolute zero, < ^ , are given i n Table 2 . Prom a consideration of Table 2 It Is evident that there i s no.difference i n properties of alloys of the form MneoPe^Algo-xCao with heat treatment. There are no consistent differences in Curie temperature or saturation magnetization between the alloys In the quenched or slow cooled state* A different situation occurs i n the alloys of the form Miieo-x^x** 2 0^ 2 0* Curie temperatures of samples in the quenched state are consistently higher than samples in the slow cooled state. The difference in O c decreases uniformly with increasing iron additions. The saturation magnetization at absolute zero of samples i n the quenched state Is measurably higher In four out of the five alloysj however, the difference In ^between quenched and slow cooled specimens does not vary uniformly. The variation of Curie temperature with perbent iron or chromium i n alloys of the form MneoXyAIzo^ypzo Is :given In f i g . 8 and with percent iron i n alloys of the form Mneo^xFexAlaoCa© in f i g . 9» In the former group, the results for both the iron system and the chromium system f a l l on a single smooth curve. In the f i r s t 350 Figure 8 The Variation of Curie Temperature with Atomic # Iron or Chromium in alloys of the form MneoX^lao^xCao 2k 2 0 I _ l , |_ 1 0 1 5 2 0 Atomic i» Iron Figure 9 The variation of Curie temperature with atomic # Iron in alloys of the form Vineor3^e:gAXzo0zo Figure 10 The Variation of saturation magnetization with temperature for three example alloys of the form M-ned^^^^zo-x^zo Figure 11 The variation of saturation magnetization with temperature for two slow cooled alloys of the form Mneo-x^x^ 2 0^ 2 0 27. Figure 12 The Variation of Bohr Magneton Value per Magnetic Atom with Atomic $ Iron or Chromium i n alloys of the form Mn^x^lzo-xCso « as > a o +» a> c 60 X) o ffl 1.20 }-1.10 k l.oo h .90 U 10 Q slow cooled samples •unassayed furnace cooled samples X quenched samples , 1 15 Atomic # iron Figure 13 The variation of Bohr magneton value per magnetic atom with atomic # alloys of the form Wtoto^j^yfilzoCzo 2 0 iron in group.it Is observed that the Curie temperatures increase strongly from s l i g h t l y below room temperature for no additions to above JOO^C for 5 percent iron. It Is important to note that the Curie temperatures are those characteristic of the alloys In a f i e l d of 16,200 oersted. The Curie temperatures i n zero f i e l d would possibly be 20° to 30° lower. The second group of alloys have a much different variation of Curie temperature with composition. The maximum Curie temperature occurs for 10 percent iron. For higher additions the Curie temperature drops quite slowly. The variation of saturation magnetization with temperature for some alloys In both groups i s shown i n f i g s . 10 and 11 for compara= tive purposes. The saturation magnetization at absolute zero In a l l cases has been converted to the JJohr magneton value per magnetic atom (Mn and Fe or Mn and Cr). The variation of Bohr magneton value with percent iron or chromium for alloys of the form MnebXxAl2o«xC2o Is given in f i g . 12. It is noted that the Bohr magneton value per atom i s decreased markedly with the addition of either iron or chromium. The results for both alloy systems f i l l on a single smooth curve. The variation of Bohr aaagneton value with percent Iron addi-tion for alloys of the form Mn£o..xFexAl2oC2o i s given in f i g . 13• No such simple variation as i n the f i r s t group i s noted. The unassayed alloys were merely checks used to confirm the shape of the curve. From assays on the other alloys i t was found that the actual composition varied from tne nominal by less than + .6#„ These are the limits shown for the points representing unassayed alloys. The variation i n Bohr magneton value over the range 10^20 percent i s much less than that occurring for the iron contents between 0 - 5 percent i n the f i r s t alloy group. Vo DISCUSSION OP RESULTS AND CONCLUSIONS The structure of M113AIC Is assumed to be as proposed by Butters and Myers ( f i g . 1 ) . Prom visual estimations of line intensities on Debye-scberrer powder photographs and the presence of extra " s u p e r l a t t i c e " lines, i t i s concluded that i n a l l single phase alloys obtained in the two groups of alloys, MneoXx^so-x 0 2 0 and MneQ=>xxxA12oC2Q> the same type of order occurred. In table 1, disregarding for the moment the two different models proposed there, i t is evident that within experimental limits the highly ordered face-centered structure occurs for the alloy of approximate composition Mn4oPe2oAl2oC2o° As the purpose of this investigation was to discover the effect of iron and chromium atoms at cube corner and body center posi-tions, i t was important to know i f the addition atoms were restricted to one type of lattice s i t e . Por example in alloys of the form Mn6oXxAl20.,xC20 i t was imperative to know i f the addition atoms ( x ) occupied solely the cube corner positions or i f some mixing of manganese and addition atoms took place. I f the latter occurred then both types of atoms would be found at "cube corner and face center positions. This complicating factor was ruled out for the following reasons. In the f i r s t group of alloys with the additions being made at the expense of aluminum the observed maximum addition possible was 5 percent iron and 3 percent chromium. In the second group, however, with the additions being made at the expense of manganese the minimum addition possible with the retention of the highly ordered single phase was 10 percent iron and 5 percent chromium. Thus i t i s assumed that in the f i r s t group (Mn 6 0X x Al2o~x c 2o) any mixing of the addition atoms and manganese atoms between cube corner and face center positions i n not possible, at least u n t i l the amount of addition equals 10 percent iron or 5 percent chromium. However the maximum additions possible do not reach these limits, therefore we conclude that in the f i r s t group, MneoXxAl20-xC2o, the addition atoms solely occupy the vacated aluminum cube corner positions. In the second group, Mn 6o-x xxA 12oC2o> i t is assumed that the addition atoms replace manganese atoms at face center positions and that no mixing of addition atoms and aluminum atoms occurs between the face center and cube corner positions. This assumption i s supported by the fact that, in the Mn-Al-C system as discussed previously, i f the manganese content i s dropped below 60 percent then a second phase i s formed. This would imply that the aluminum atoms are unable to occupy face center posi-tions. For the alloy of nominal composition Mn^oFeaoAlaoCso (actually Mn39»eFe2o«3Al2o°7Cxe«>5) i t was thought that perhaps ordering of the manganese and iron atoms amongst the face center positions occurred. X-ray line intensity calculations and measurements as given i n table 1 are of l i t t l e help. The atomic scattering factors of iron and manganese are much too similar to allow any large differention between random mixing of the iron and manganese atoms at the face center positions and an ordering of these atoms in some way. It i s , however, noted that in a l l calculated intensities which d i f f e r between the two models, those intensities based on the p r e f e r e n t i a l position of iron are closer to the measured values, although i n some cases very sl i g h t l y . This then is some very slight evidence for assuming a preferrential ordering of the iron atoms in this alloy amongst the face center positions. It would be necessary~to have more conclusive evidence which at this time Is not available, before any conclusion along these lines i s reached. As mentioned before, the variation of lattice parameter with percent iron in.alloys o f t h e form MneoFexAlao=xC2o ( f i g . 5) is quite peculiar. It i s d i f f i c u l t t;o understand why the parameter should f i r s t increase with small additions of iron and then decrease with further additions. A plausible explanation of this was thought to be found after a consideration of the variation of Curie temperature for the same alloy group ( f i g . 8). These Curie temperatures are those appropriate to an external f i e l d of 16,200 oersted % therefore the Curie tejaperature In zero external f i e l d would be about 20 to 30°C lower. The Curie temperature in zero f i e l d of MnaAlC would then be below room temperature, whereas the Curie temperatures of alloys con= taining iron were well above room temperature. Therefore the measured lattice parameter of MnsAlC i s characteristic of the paramagnetic state whereas the parameters of the other alloys are characteristic of the farromagnetic state. I f the parameter of M113AIC contracted as i t passed through the region of the Curie temperature then a plot of the variation of parameter characteristic of the magnetized state would have simply revealed a decrease as iron was added. However, such was not the case. The variation of parameter of MnaAlC with temperature revealed that the parameter expands through the region of the Curie temperature ( f i g . 7)» This would make the maximum In the parameter-composition curve much more pronounced i f parameters characteristic of the ferromagnetic state were used. At this time no discussion i s put forward to explain this unusual behaviour. The parameter-composition curve for alloys of the form Mneo-xPejjAlao C20 is simply a linear decrease of parameter with increasing percent iron. This would imply that the iron atoms i n the face-center positions are smaller than the manganese atoms they are replacing. Magnetic Properties The.-Bffi^netlc properties of the two alloy groups are very different. In the class of alloys of the form Mnec—XFexAl2oC2o the magnetic properties do not lend themselves to any straight forward interpretation, there being no regular variation in Bohr magneton value. It should be noted, however, that the average magnetic moment of the iron and-manganese atoms i n these alloys i s less that observed for the manganese atoms in MnsAlC. Por the-alloy group of "the form MneoXxA^o-xCao* replacing aluminum by-iron or chromium causes a pronounced regular decrease in the Bohr magneton number per atom. Pig. 12 shows that additions of either iron or chromium produce ~the same effect. An interpretation of these results i s complicated by the fact that i t i s not known how the aluminum content affects the magnetization of the alloy. Lacking an appreciation of the exact mechanism governing the structure and magnetic properties of these alloys i t i s convenient to describe the properties in the following manner. It" i s assumed that the moment of the manganese atoms Is constant In a l l alloys. On this assumption a moment of 5 Bohr magnetons aligned anti»parallel to the manganese moments must be attributed to the addition atoms. This representation accurately f i t s the results and may be compared with values obtained in other alloys. In a l l alloys of the form Mngo +y^zo> where Y has been zinc, gallium, or aluminum a representation similar to that above has necessitated an allowance of =4 Bohr magnetons to the manganese addition atoms occupying cube corner positions. We do not wish to stress the difference between the behaviour of manganese on the one hand and iron and chromium on the other since i t i s very d i f f i c u l t to obtain measure^ ments of the applicable moments within the limits of t 1 / M & » This is even true of binary systems where the available range of composition is limited. The important aspect Is the high value of the assigned moment necessary to account for the observed results. Before any further interpretation of these alloys i s attempted, i t w i l l be necessary to know the effect of the corner atoms, aluminum and zinc, on the magnetization. Work on the alloy system MneoAlxZnao„xC2o has been completed (L. Howe 1956) and has shown that no simple valency mechanism governs the contribution of the corner atoms to the magneti-zation. Neutron diffraction experiments would be very useful on both alloy groups, that i s , iron and chromium additions at face center and cube corner positions. In particular in the alloy system MneoXxAl20<=xC20 neutron diffraction experiments would reveal whether the actual magnetic structure i s as represented. VI. APPENDIX Calculation of Bohr magneton values for additiin atoms In alloys of the form Mne6&xb'Lso~xCzo It Is assumed that the moment of the manganese atoms occupying face center positions i s constant and equals 1.23/^ . A net moment ^fl3 i s assigned to the addition atoms occupying cube corner positions. Then, for any addition concentration X, the measured Bohr magneton value _^4P7 can be represented as (60+x)^ . xjJ, + 60(1.23) therefore ^ - (60-fx)^L -60.(1.23) x The value ofyt^t which best satisfies the experimental results for both Iron and chromium additions i s -5 /Ja • 57-VII. BIBLIOGRAPHY 1. Ro G. Butters and H. P. Myers. P h i l . Magy,. Ser. 7* p° 895* 1955(A) 2. R. G. Butters and H. P. Myers. P h i l . Mag.. Ser. 7, P° 132, 1955 (B) 3. R. W. James, The Optical Principles of the Diffraction of X-rays, London? G. B e l l and Sons, (19^8). 4. K. Hoselitz, Ferromagnetic Properties of Metals and Alloys 8 Oxford University Press, (1952). 5. D. H. Polonis, Doctor's Thesis, University of B r i t i s h Columbia, pp. 86-89, (1955). 6. L. Mo Howe, Master's Thesis, University of Br i t i s h Columbia, (1956)°