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The structure and magnetic properties of some ternary alloys containing manganese and boron Swanson, Max Lynn 1954

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THE STRUCTURE AND MAGNETIC PROPERTIES OF SOME TERNARY ALLOYS CONTAINING MANGANESE AND BORON by MAX LYNN SWANSON A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF'SCIENCE in the Department of METALLURGY We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF SCIENCE. Members of the Department of Metallurgy. THE UNIVERSITY OF BRITISH COLUMBIA October, 1954. ABSTRACT Binary alloys of manganese and boron and ternary alloys of manganese and boron with aluminum, zinc, t i n and indium were prepared. Their structures were determined from x-ray powder photographs, and their ferromagnetic properties were measured with a Sucksmith r i n f balance, using a powerful electromagnet. The orthorhombic phase MnB had a ferromagnetic Bohr magneton number of 1.73 per molecule and a Curie point of 309°C. Most of the ternary alloys were slig h t l y ferromagnetic, but no strongly ferromagnetic single phase regions were found. Paramagnetic measurements on Heusler alloys showed that they followed the Curie-Weiss law for the. restricted range of temperature i n which measurements could be made. ACKNOWLEDGMENTS The author i s grateful for assistance rendered by members of the staff of the Metallurgy department, especially his research director, Dr. H. Myers, and Mr. R. Butters. The work was done with the help of funds provided by the Defense Research Board under Research Grant 281. TABLE OF CONTENTS Page I. INTRODUCTION t 1 II. MAGNETIC MEASUREMENTS Theory .. 5 Apparatus. , •>• 5 III. X-RAY MEASUREMENTS 9 IV. SUMMARY OF WORK DONE 10 V. PREPARATION OF ALLOYS 11 VI. RESULTS 1. Manganese-Boron alloys 13 2. Manganese-Aluminum-Boron alloys . . . . . . . . . . 21 3. Manganese-Zinc-Boron alloys . . . . . . . . . . . . 23 4. Manganese-Tin and Manganese-Tin-Boron alloys . . . . 27 5. Manganese-Indium and Manganese-Indium-Boron alloys . 30 VII. PARAMAGNETIC ^ ASUREMEKTS ON.HEUSLER. ALLOYS 31 VIII. DISCUSSION O F R E S U L T S AND CONCLUSIONS 38 IX. BIBLIOGRAPHY 41 ILLUSTRATIONS Page 1. The ferromagnetic ring balance . . . . . . . . . . . . 7 2. Pole pieces producing a uniform f i e l d gradient 7 3. Ferromagnetic Curie point determination for MnB 17 4. Magnetic moment per unit mass divided by saturation moment, CT/tf0 against absolute temperature divided by ferromagnetic Curie point, T/Op 18 5. The determination of the saturation moment at absolute zero of MnB« « 0 « e « s o o e o o o o o o e e 9 0 * 0 0 0 0 • • • • • • 19 6. The paramagnetism of MnB 20 7. Manganese-aluminum-boron ternary diagram showing phases at room temperature, . o o o . o o o . . . . . . . . . « o . . . . . . . 22 8. Manganese-zinc-boron ternary diagram showing phases at room temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 25 9. Manganese-tin-boron ternary diagram showing phases at room temperature 29 10. The paramagnetism of Cu2MnIn • 34 11. The paramagnetism of Cu2MnAl 35 12. The paramagnetism of CuaMnAl 36 13. The paramagnetism of Cu2MnSn 37 THE STRUCTURE AND MAGNETIC PROPERTIES OF SOME TERNARY ALLOYS CONTAINING MANGANESE AND BORON I. INTRODUCTION It was assumed by Langevin that a paramagnetic substance consisted of non-interacting atoms or molecules, each having a permanent magnetic moment. If i n a magnetic f i e l d these moments are distributed s t a t i s t i c a l l y , the magnetic susceptibility of the substance iss X = (D T where C i s the Curie constant of the substance, and T i s the absolute temperature. i s defined as the magnetic moment per unit mass, C , divided by the applied f i e l d , H. Weiss modified the Langevin theory by considering that 1 interactions between atoms produced an internal f i e l d which was pro-portional to the magnetisation or magnetic moment.per unit volume, I. This f i e l d , NI, is added to the external f i e l d to give the effective f i e l d : H e - H + NI N i s the Weiss inter-molecular f i e l d constant. The Curie-Weiss law results from substituting this effective f i e l d for the applied f i e l d :'. i n equation ( l ) : 2 6 i s the paramagnetic C u r i e p o i n t . Fo r a gram molecu la r weight o f subs tance , o • N/> crQl? , N ^ C M 3 RM M where y » i s the d e n s i t y , i s the gram molecu l a r s a t u r a t i o n magnetic moment, R i s t he gas constant and M i s the mo lecu l a r we igh t . I f N 'and thus & are p o s i t i v e , the substance i s f e r romagne t i c , because, as can be shown, the re may e x i s t below T = 0 a spontaneous magne t i s a t i on i n the subs tance . Th i s magne t i s a t i on inc reases as T decreases , approaching a maximum as T approaches z e r o . Fo r T g rea te r than 9, equa t ion (2) i s t r u e , and the substance i s paramagnet ic . The spontaneous magne t i s a t i on of a body i s d i r e c t e d d i f f e r e n t l y i n d i f f e r e n t r e g i o n s , c a l l e d domains. The r e s u l t a n t magne t i sa t ion i s z e r o , because o f the random d i s t r i b u t i o n of the magnetic d i r e c t i o n s . Only a r e l a t i v e l y s m a l l e x t e r n a l f i e l d i s r e q u i r e d t o l i n e up the d i r e c t i o n s o f magne t i s a t i on , and thus make the body fer romagnet ic as a who le . Expe r imen ta l evidence ( e s p e c i a l l y gyromagnetic r a t i o measure--ments) i n d i c a t e s t h a t the magnetic moment f o r fe r romagnet ic substances i s caused by e l e c t r o n s p i n . The moment of a s p i n n i n g e l e c t r o n i s one Bohr magneton, - eh = 9.27 x 10 Z ' e rg /gauss , where e and m are the charge ZtfTinc and mass o f the e l e c t r o n , and h i s P l a n c k ' s cons t an t . A p a i r o f e l e c t r o n s p i n s can be d i r e c t e d o n l y p a r a l l e l o r a n t i p a r a l l e l . I f i n t e r a c t i o n s cause an excess o f s p i n moments t o p o i n t i n one d i r e c t i o n , spontaneous magne t i s a t i on e x i s t s . The c o l l e c t i v e e l e c t r o n t h e o r y presents a model o f the m e t a l l i c s t a t e which i s more r e a l i s t i c than t ha t o f W e i s s , Outer e l e c t r o n s o f atoms are thought o f as shared c o l l e c t i v e l y through the subs tance . Al though 3. this model leads to satisfactory results for simple substances, such as nickel and its alloys with copper, the quantum mechanical problems involved in the study of more complex substances are too difficult to be solved. Atomic interactions are mainly due to the outer electron shells. Heisenberg postulated that the exchange interaction energy between the same shells (i.e.? 3d shells of transition metals) of adjacent atoms could be positive, in which case the electrons line up with parallel spins, producing ferromagnetism. This postulate has had as yet no quantitative theoretical verification. Zener^, on the contrary, postulated that the exchange energy between adjacent atociic 3d shells of transition metals was always negative, and that ferromagnetism was caused by coupling between 3d and As shell electrons of the same atom. The results of this assumption are not in good agreement with observed properties. Using Heisenberg*s postulate, Slater^ and Bethe have assumed the following variation of the exchange energy, J, with the ratio of the internuclear distance, D, to the 3d shell diameter, d. O —-ryCo It is seen from this curve that the exchange energy is positive and large enough to cause ferromagnetism for values of D/d slightly greater than 1.55 (e.g.* Fe, Co and Ni). Thus paramagnetic manganese, with a ratio only slightly less than 1.55, could become ferromagnetic i f i t s internuclear distance were increased so that D/d became greater than 1.55o This increase occurs for ferromagnetic manganese alloys and compounds: Alloy: Cu2MnIn Cu2MnAl Cu2MnSn D/d : 2.98 2.84 2.97 Previous work in the University of British Columbia Metallurgy department has shown that an ordered face-centered cubic ferromagnetic phase occurs i n the ternary alloys of manganese and carbon with a metal (X) having high valency and a positive size factor with respect to manganese. Aluminum, zinc, t i n and indium were used success-f u l l y i n this capacity. The optimum composition for this phase i s MnaXCj carbon occupies the body centered position. This work suggests that similar alloys with the carbon replaced by boron or nitrogen may exist. In the work to be described, boron alloys with similar structures and magnetic properties to those containing carbon were sought. L i t t l e i s known about binary boron alloys and none about the ternary alloys considered. 5. II. MAGNETIC MEASUREMENTS Theory. Magnetic measurements of the saturation magnetic moment per unit mass, CT , and the susceptibility, , were required. The principle for the determination of these quantities i s the measurement of the force exerted on a specimen of mass m when placed i n an inhomogeneous magnetic f i e l d . This force i s : F = CTm a_H = X m H d-x The method used was based on a comparison of the specimen having unknown CT and jC with a standard substance. If H ^  H i s kept constant while the force i s being measured for the specimen and t h e standard, CT and .X can be determined without knowing the value of H 3 H , since • X; m^  9-X — F2 -*» "2 Apparatus; (a) The Magnet: The magnetic f i e l d was produced by an electromagnet of the Weiss type, built by R. Shier and G. Kidson^ while i n this department. A maximum f i e l d of 21,500 gauss could be attained. To produce a constant v e r t i c a l f i e l d gradient, the pole pieces were shaped as shown in figure 2. ": (b) The Ferromagnetic Balance: The force exerted on a ferromagnetic specimen placed i n t h e region of constant f i e l d gradient was measured using a Sucksmith ring 6. balance (Figure 1 ) . The deflection of a light beam reflected from mirrors suitably attached to the beryllium copper ring was proportional to the force distorting the ring. A molybdenum rod was used to connect the ring to a platinum iridium collar, into which a cylindrical platinum iridium specimen box could be placed. A very convenient specimen size of only t h i r t y milligrams was normally needed. Pure iron was used as a standard. (c) The Paramagnetic Apparatus; The paramagnetic apparatus differed from the ferromagnetic apparatus only i n the following particulars! (i) the balance was similar but more sensitive, ( i i ) the molybdenum rod was replaced by a s i l i c a tube, ( i i i ) the specimen was either machined into a ring shape or carried i n a carbon capsule. It was attached by means of a wire clamp placed in a groove at the bottom of the s i l i c a tube (see sketch), v ;! „ s i l i c a tube specimen clamp thermocouple A specimen size of only 100 mg. was adequate. Allowance was made for specimen carrier deflections. Nickel was used for calibration. Some sizes for the ring balance are: Ring diameter » 6 cm. Ferromagnetic ring: 3 mm. by o,3 mm. thick; s p i r a l springs: 0.3 mm. thick. Paramagnetic ring : 3 mm. by o . l mm. thick; s p i r a l springs: 0 o l mm. thick. Balance Mirrors O i l Damping -Q Microscope Beryllium Copper Ring Specimen Box •* Molybdenum rod n = H ^ [ ] - - C 3 ^ -Flat Spiral Springs Figure 1: The., ferromagnetic ring balance _ uniform f i e l d _ gradient Figure 2s Pole pieces producing a uniform field gradient. 8. (d) High and Low Temperature Apparatus: For low temperature magnetic measurements the specimen was suspended just above liquid oxygen i n a Dewar flask. A copper-constantan thermocouple i n conjunction with a potentiometer, a standard c e l l and a galvanometer was used to measure the temperature. High temperature measurements were made i n a specially constructed water cooled furnace. A platinum-platinum rhodium thermos couple was used. The ring balances and high and low temperature apparatus were built by H. Myers and R. Butters of this department. 9. III. X-RAY MEASUREMENTS A Philip's x-ray machine and Straumanis type powder cameras were used to take photographs of samples of a l l the alloys. The resulting Debye-Scherrer powder patterns were measured. Film shrinkage known to correspond to a Bragg angle of 9 0 ° . 2 The films were indexed by using the ratios of the sin 9 values of the lines; the equation for sin^O in the cubic system i s : where 9 i s the Bragg angle, ^ i s the wave length of the x-radiation, a i s the parameter of the unit c e l l , and h, k , 1 are the indices of the reflecting plane. Parameters were calculated from the same equation, and plotted against the Taylor-Sinclair function to eliminate the error caused by absorption of x-rays by the specimen. effects were eliminated by referring a l l distances to that distance sir^O = 7? ( h2 + k2 + ]2) IV. SUMMARY OF WORK DONE. The following alloy systems were investigated: 1. Mn - B 2. Mn - Al - B 3. Mn - Zn - B 4. Mn - Sn - B 5. Mn - In - B Other binary alloys were made to aid i n identification of phases. Magnetic measurements were made on ferromagnetic alloys, MnB i n particular. Paramagnetic measurements were also made for some Heusler alloys. u V. PREPARATION OF ALLOYS Two methods of preparation were used: (1) Induction Melting: The alloy components were heated in alumina crucibles under argon at atmospheric pressure by induced eddy currents. The melts were c h i l l cast into a brass mould i f possible. The resulting ingots were homogenized i n evacuated s i l i c a tubes or under an argon atmosphere. Samples were mounted i n lucite and examined microscopically. ( 2 ) Sintering: Because of the d i f f i c u l t y i n melting by induction alloys, containing zinc or a large proportion of boron, they were prepared by sintering intimately ground mixtures of their components. The mixtures were heated i n evacuated s i l i c a tubes containing very l i t t l e free volume. The following alloys were sintered: 1 Alloy Sinter Components Temperature (°C) Time (hr.) • MnB Mn;B 950 - 1050 7 2 MnAl2B MnAlgjB 9 0 0 72 Mn6Al3Bn ;MnAl2;MnjB 9 0 0 , 72 " A l l Mn-Zn-B MnjZnjB 9 0 0 72 MnSnB MnSn;B 6 0 0 75 MnlnB MnlnjB 1000 48 12 were: The materials used i n the preparation of the alloys Manganese: 99.9% purity, donated by the Electromanganese Corporation of America. Aluminum : 99.99$ purity, donated by the Aluminum Company of Canada. Zinc : dust; 93$ purity (major impurity being oxygen) Tin : 99.99% purity Indium : 99.99% purity, donated by the Consolidated Mining and Smelting Company of Canada. Copper : 100.0$ purity Boron : 'pure amorphous' and 99.2$ purity. 13.-VI. RESULTS 1. Manganese-Boron Alloys; Previous Work; Heusler6 (1904), Jassoneix7 (1906) and Wedekind8 (1907) first investigated manganese-boron alloys. They reported that only MnB was ferromagnetic. H. Forestier and M. Graff (1936) found the Curie point of MnB to be about 300°C. R. Hocart and M. F a l l o t 1 0 (1936) evaluated the moment of the manganese atom in MnB at 9.65 (* 5%) Weiss magnetons; they discovered the structure to be orthorhombic with eight MnB per unit cell and with parameters a = 2095> b = 11.5, c = 4.10A. R. Kiessling 1 1 (1950) found four manganese-boron phases: MnB : orthorhombic: a = 5.560, b «= 2.977, c = 4.145A with 4 MnB per cel l . Mn3B4. : orthorhombic: a = 3.032, b = 12.86, c « 2.960A with 2 Mn3B4 per cel l . Mn2B : tetragonal: a = 5.148, c = 4.208A with 4 Mn2B per c e l l . to^l* : orthorhombic: a = 14.53, b = 7.29, c w 4.21A with 8 Mn^ B per cell. Only MnB was ferromagnetic. 14. Results: The results are tabulated: Alloy Heat Treatment Phases at Room Temperature Ferromagnetism MnB c h i l l cast; homogenized sintered MnB; Mn2B MnB strong (f0 =147} 0F= 309° C Mn 5«B 4 6 homogenized 50 hrs. at 1000°C. MnB; Mn2B <T0 =100 Mn5gB4.2 homogenized 50 hrs. at 1000°C. Mn2B; MnB oj , = 50 Mn2B homogenized 50 hrs. at 1000°C. Mn2B; Mn^B;-©* - Mn None Mn3B c h i l l cast homogenized 50 1000°Co Mn2B; <<- Mn Mn2B; Mru,.B; << - Mn . None None homogenized '50 1000°C. Mn^ B; e< - Mn None The phases MnB, Mn2B and Mn^ had the same structures and parameters as those found by Kiessling. The ^ - manganese phase seemed to be almost as stable as the Mn2B and Mn^ jB phases, since i t occurred i n the alloys Mn2B, Mn3B and Mn^ B even after homogenization. .It i s possible that impurities in the boron stabilized the «i - Mn phase. The sintered alloy MnB was single phase, but the induction melted MnB, which was only s l i g h t l y off composition, had a l i t t l e Mn2B phase present. Thus the range of composition for the single phase, MnB, is narrow. Magnetic Properties: The magnetic properties of the MnB phase were investigated for two different specimens: (l) For the f i r s t specimen, the magnetic moment per unit mass, & , was 136 ergs per gram per oersted at 20°C.(measured using a f i e l d of 16,000 gauss). If CT i s plotted against absolute temperature 15. squared, T , at low temperatures, a straight line results, which when extrapolated to absolute zero gives the saturation moment, 0'o . Such a line was plotted for the MnB specimen, using temperatures down to 140°Kj the resulting value of &o was 147. The ferromagnetic Bohr magneton number for a molecule of a substance having gram molecular weight M i s Pg = M 0t> . For the MnB, 5585 P B " 65.75 x 147 = 1.73/tB per MnB molecule, or per manganese atom. 5585 For purposes of comparison, this i s almost identical with the value for pure cobalt: Pg = 1.72 . The ferromagnetic Curie point, 9 p , of MnB was determined by-plotting CT% against T (Figure 3 ) . This plot produces a straight line near the Curie point, which was found to be 3G9°C. Also, °/f(f0 was plotted against T/9p (Figure 4 ) . As this curve i s generally structure sensitive, the plot for MnB differed from that for nickel. (2) For the second specimen the results were: cr = 132 cr0 = 143 (Figure 5)j P B = 1.68 9 F = 304°C. This specimen probably had a small amount of a second phase present. Paramagnetic measurements were made on this MnB specimen. The paramagnetism followed the Curie-Weiss law (Figure 6): 16 The values calculated for the constants were s C = 1,48 x 10" per gram and the paramagnetic Curie point, 9 = 305°C, This value agrees well with the ferromagnetic Curie point of 304°C, . The paramagnetic Bohr magneton number, Pg = 2,828 VCM per molecule. For KnB, P B = 2,79 per molecule. The ratio between this value and the ferro-magnetic Bohr magneton number, 1.68, is of the usual order of magnitude. 17. 140 120 -100 80 60 40 20 - --•v 1 ^ 1 V I -\ \ v 1 \ 1 ^ h \ v - • \ \ \ \ \ l \ \ • - o --\ V p 0 : <? against T • : C z against T • 7000 6000 5000 m 4000 3000 2000 - 1000 150 200 250 T(°C.) 300 0 Figure 3: Ferromagnetic Curie point determination for MnB ( f i r s t specimen): Magnetic jnoment per unit mass, CT. and moment squared, CT, against temperature, T. 18. 1.00 0.80 0.60 0.40 0.20 O MnB • Nickel 0.20 0.40 0.6a, T/e, 0.80 1.00 Figure 4: Magnetic moment per unit mass divided by , saturation moment , cf/tT0 , against absolute temperature divided by ferromagnetic Curie point, T/Op,. 130 U 1 1 J L 1 0 15,000 30,000 45,000 60,000 75,000 T V K . ) Figure 5: The determination of the saturation moment at absolute zero of MnB (second specimen): Magnetic moment per unit mass,0", against 2 absolute temperature squared, T • 4.0 20. • Temp, decreasing I I _ J I ±J 450 550 650 750 850 T(°C.) Figure 6: The paramagnetism of MnB (second specimen): The inverse of susceptibility, 1/x (X is measured i n ergs; per gram per oersted), against temperature, T. 21. 2. Mangane s e-Aluminum-Boron.- Alloys Previous Works No previous work has been done on Mn-Al-B alloys. The 12 phase diagram of the Mn-Al system i s well known. Results; A l l alloys were homogenized for 50 hrs. at 800 to 1000"C. The main phases occurring were^-manganese, MnB, Mn2B, and the body-centered cubic 3" phase of the manganese-aluminum system (Figure 7 ) . The Mn2B phase had slig h t l y larger parameters than i t had in the binary alloys. The alloy MnAl 2 was made i n order to obtain the phase. The results were as follows; Alloy Heat Treatment Phases at Room Temperature Fe rromagnet ism Mh 6Al 3B /3 -Mn; cubic slight Mn^.sAl^.5B 2? cr= 15.7;©F = 310°C Mn 3Al 6B as-cast homogenized MnB slight hone Mn 3Al 2B y ;MnB C = 43.9;6^ = 310°C Mri 2Al 2B r ;MnB medium MhAl2B as-cast homogenized or sintered MnB slight medium Mn^lB /3 -Mn; Mn2B none Mn3AlB /3 -Mn; Mn2B none Mn 2. 5AlB as-cast homogenized / MnB;/? -Mn ?-Mn;Mn?B;MnB medium <r = 27.0 Mn2AlB - T ,MnB cr= 56.9;6F - 310°C Mn 1 > 5AlB 5 , MnB ^=67.3' MnAlB as-cast homogenized MnB cr = 6 6 . 0 ;j none MneAlaBii sintered r = 22.9; ^ =71.2 2 2 . Mn 80 kMn*B 40 M n A l a 30 20 / Mn 60 50 • 70 0 • / 3 - M n /3 -Mn + Mn 2 B / • • /tf-Mn+_MnaB + MnB I O o S' + MnB o Mn 3 B A. 30 Mn 2 B ,40 B \ 80 70 60 50 40 30 A l 20 10 F i g u r e 7s Manganese-Aluminum-Boron Ternary Diagram Showing Phases a t Room Temperature • denotes non-ferromagnetic a l l o y O denotes ferromagnetic a l l o y 23. Where no heat t reatment i s g iven i n the T a b l e , the a l l o y s had the same s t r u c t u r e s before and a f t e r homogeniza t ion , and the magnetic measurements app ly t o the homogenized a l l o y s . I t i s seen tha t the a l l o y s M n 3 A l 6 B , M n A l 2 B , M n 2 . s A l B and MnAlB are the o n l y ones h a v i n g uns table phases i n the a s - c a s t s t a t e . The important uns tab le phase i s MnB, which forms r e a d i l y i n a l l o y s w i t h h igh boron and low manganese con t en t . The ferromagnet ism o f the M n - A l - B a l l o y s prepared was l a r g e l y due t o the MnB phase. 3 . M a n g a n e s e - Z i n c - B o r o n - A l l o y s . P rev ious Work; No p rev ious work has been done on Mn-Zn-B a l l o y s . For the Mn-Zn system, the phase diagram from zero t o f i f t y weight percent z i n c was s t u d i e d by E . P o t t e r and R . H u b e r ^ (1949). Room temperature phases were ot - Mn; /3 - Mn, and «< - Z n . <* - Zn i s f ace -cen te red cub i c w i t h f o u r atoms per u n i t c e l l . I t i s formed by decomposi t ion o f £ (which i s c l o s e packed hexagonal w i t h two atoms per u n i t c e l l ) o n l y a f t e r v e r y s low c o o l i n g t o room tempera ture . The phase diagram from f i f t y to one hundred weight percent z i n c was s t u d i e d by Schramm^ (1940). 24. R e s u l t s ; The a l l o y s were s l i g h t l y fe r romagnet ic f o r a l a r g e range o f c o m p o s i t i o n . The a l l o y s and t h e i r p r o p e r t i e s are l i s t e d (F igure 8 ) : A l l o y Phases at Room Temperature B r i t t l e n e s s Ferromagnetism Mni]_Zn 7 B 2 50% ot - Mnj 45% 8 m a l l e a b l e 'medium ' M n d Z n 1 0 B 2 60% « f - Mnj 30%. 9 mal l eab l e s l i g h t Mn 6ZnB 75% /3 - Mnj 25% Mn*B b r i t t l e none Mn 3 ZnB 75% Mri^B s l i g h t l y b r i t t l e s l i g h t Mn 2 ZnB 50% ^ - Mn; 50% M n ^ b r i t t l e • v e r y s l i g h t M n ^ Z n B 50% oi - Mn; 25% Mn^B; 25%, I b r i t t l e medium MnZnB 50% K b r i t t l e C = 56, C0 = 64 ; remanent M n 0 5 Z n B 60% Zn; 30% SL mal l eab l e none Mn]_oZn 3B 7 75% Mn 4 B b r i t t l e medium MnQZnB^o 80% <p b r i t t l e (f = 104; remanent M n 8 Z n 2 B 1 0 70% <j> ;! 30% SX. b r i t t l e s trong;remanent Only the f i r s t two l i s t e d a l l o y s r e q u i r e d a n n e a l i n g a f t e r f i l i n g t o produce good x - r a y photographs. Phases o c c u r r i n g were: (1) /3 - Mn and Mn^B: These phases are w e l l known. (2) Body-centered cub ic o(. - Mn types Th i s phase was s i m i l a r t o t< _ Mn, and had parameters a Q = 8,888 A f o r Mn„ Zn7B2 and a Q = 9.169A* f o r Mn 2 ZnB, I t was s l i g h t l y t e t r a g o n a l f o r the M h 8 Z n 1 0 B 2 a l l o y . (3) 6, a cub i c s t r u c t u r e , p robab ly ordered f ace -cen t e r ed c u b i c : I t s parameter was 3.918A f o r Mni]Zn7B2. ® w a s p robab ly fe r romagne t ic o n l y 25. •* Zn Figure 8: Manganese-zinc-boron ternary diagram showing phases at room temperature. • denotes non-ferromagnetia-alloy O denotes ferromagnetic alloy 26. i n the ordered state, since most of the ferromagnetism of Mn^Zn7B2 was lost by f i l i n g , (4) The pure zinc phase l i s t e d for the alloy Mn0>5ZnB: This i s possibly not pure zinc, but a phase with the same structure and parameters, (Such phases occurred for the Mn-Sn-B and Mn-In-B systems). (5) -ft- , a non-magnetic phase of unknown structure occurring i n the' alloys MnQ t;ZnB and MngZnaB^Q0 (6) The 0 and \\ phases, which were strongly ferromagnetic: The 0 phase was almost as magnetic as MnB. It occurred i n the alloys MngZnB^o an& MngZn2B/0 , which were prepared to demonstrate that zinc would not replace manganese to any appreciable extent i n MnB, The J\ phase was present in the alloys Mnn ZnB and MnZnB, Both (j> and h had complidated structures. 27. 4. Manganese-Tin and Kanganese-Tin-Boron Alloys. Previous Works The manganese-tin system has been investigated by Pott e r 1 5 (1931), Guillaud 1 6 (1943), Nowotny and Schubert 1 7 (1943) and N i a l 1 8 (1947). Potter found for alloys annealed at 450 to 500°Cs Mnj^ Sn was' weakly ferromagnetic with Op = 150°C. Mn2Sn was strongly ferromagnetic with 9p = 0°C. MnSn was not ferromagnetic. Nowotny and Schubert reported the following structures: MnnSn 3 ; cph. with 2a = 5.65, c = 4-506A, - = 1.595 Mn2Sn s a = 4.392 - 4.370, c = 5.457 - 5.475A, c = 1.242 - 1.250j crystaliographically like the a • f i l l e d up» NiAs type. MnSn2 s tetragonal with a = 6.647, c <= 5.434A, - = 0.817. a Nial found the same phases with almost the same parameters except that Mn]jSn3 had a = 5.66A Results: A. The following Mn-Sn alloys were melted: Alloy Phases at Room Temperature Ferromagnetism MnSn 75% MnSn2; 25% Mn2Sn medium at low temp.. Mn2Sn 90% Mn2Sn medium at low temp. Mn^Sn 90$ Mn1:LSn3 medium at low temp. The phases MnSn2, Mn2Sn and Mn„ Sn 3 had the same parameters as found by Nial. 28 B, Mn-Sn-B alloys prepared were (Figure 9)s Alloy Phases at Room Temp, Brittleness Ferromagnetism Mn-^SnB 80%/Q - Mn b r i t t l e none Mn6SnB 75% Mn^na br i t t l e medium at low temp. Mn3SnB 75% Mn2Sn br i t t l e medium at low temp. MnSnB 80% 0 ; 20% MnSn2 malleable 0".= 33.8; remanent Mn^SnsBa 80% Mn2Sn br i t t l e medium at low temp. Mn^Sn 2 B5 50% Mn2Bj 30% Mn2Sn (possibly unstable) b r i t t l e medium at low temp. Mn^rilZt? 3 70% Sn; 20% MnSn2 malleable slight at low temp. o The /3 - Mn phase of Mn-j^ SnB n a d parameter, a Q = 6.488AV The 9 phase was body-centered tetragonal with the same parameters as pure tins a = 5.831, c = 3.181A. This phase was the only ferromagnetic phase found, other than the binary Mn - Sn phases. It was strongly remanent. 29. Figu re 9s ,Manganese-t in-boron t e r n a r y diagram showing phases at room temperature . • denotes non-ferromagnet ic a l l o y O denotes fe r romagnet ic a l l o y 30. 5. Manganese-Indium and Manganese-Indium-Boron Alloys. Previous Works Zwicker^ (1951) found room temperature phases for the Mn-In system to be o< - Mn, Mn3In and indium; Mn3In had a V 20 0 - brass structure. Shirokoff's results agreed with these, except that the alloy Mn^In had a - Mn structure. No ferro-magnetic phases were found. Goeddel and Yost^l (1951), however, reported ferromagnetism from 3 to 55 weight percent manganese. Results; A. Mn-In alloys prepared were: Alloy Phases at Room Temp. Brittleness Ferromagnetism Mn9In /3 - Mn very b r i t t l e none Mn3In y b r i t t l e none Mnln iT i In very malleable none The Y phase was that previously reported. These results agree with those of Shirokoff. B,. Mn-In-B alloys prepared were; Alloy Phases at Room Temp. Brittleness Ferromagnetism Mn6InB 50% y ; 40% Mn2B br i t t l e none Mn3InB 60% Mn2B; 30% In malleable none MnlnB 90% 9 malleable medium /3 - Mn could be retained i n MtiglnB by quenching. The ferro-magnetic 9 . phase had the same structure and almost the same parameters as indium, which i s face-centered tetragonal with a = 4.594A and c - 4.951A. This phase corresponds to the 9 phase of the Mn-Sn-B system. 31. V I I . PARAMAGNETIC MEASUREMENTS ON HEUSLER ALLOYS. Procedure? S i n g l e phase Heus le r a l l o y s were prepared by i n d u c t i o n m e l t i n g and were homogenized. Powders were annealed and r a p i d l y quenched to r e t a i n the ordered s i n g l e phase. R e s u l t s ; The f o l l o w i n g a l l o y s were prepared: Alloy Annealing Temp, ( 8C) Parameter (A) Cu2MnIn 530 6.2084 Cu2MnAl 800 5.9502 Cu „ Mn ^Al 2.97 0,982 850 5.9167 Cu2MnSn 680 6.1654 Cu-^MngSna 640 Paramagnetic measurements were made on the f i r s t four l i s t e d alloys while they were cooling from temperatures near their melting points. The inverse of the susceptibility, w a s plotted against temperature, T, giving the following results: 1. The curve (Figure 10) for Cu2MnIn was slig h t l y convex toward the temperature axis. This behaviour i s common for ferromagnetic phases. The Curie-Weiss law was used for a straight line drawn through the high temperature points to calculates C - 1.41 x 10 per gram and 0 = 328°C. (The ferromagnetic Curie point i s 233°C). The paramagnetic Bohr magneton number was calculated to be. 5.78/Cg per molecule. This value compares favourably with the ferromagnetic value, pB = 4j4/tg per manganese atom. 32. 2. The curves (Figures 11 and 12) for Cu2MnAl and Cu3MnAl were similar. Both had straight line sections for a range of 200°C above the Curie point, and thus obeyed the Curie-Weiss law for this range. The calculated constants were? Cu2MnAl i C = 4.96 x 10" 3 per gram; 0 = 283°C. — Cu3MnAl s C • 4.85 x 10~3 per gram; 0 - 175°C. The ferromagnetic Curie point, 0p, of Cu2KnAl i s 330°C. As 0 p is generally almost the same as the paramagnetic Curie point, 6, these two values conflict. However, when Cu2MnAl was cooled rapidly, the curve was depressed toward the temperature axis, and 0 was raised to 350°C (+ 10°), which i s about the expected value. The difference between the two curves for Cu2MnAl was probably caused by a loss of order i n the more slowly cooled alloy. No such difference occurred for Cu3MnAl. 3. The curve (Figure 13) for Cu2MnSn was a straight line from 400 to 600°C. The constants weres C = 3.92 x 10~3 per gram. Q - 219°C. The discrepancy between this value of 0 and 340°C for 0 p i s possibly caused by a loss of order in Cu2MnSn while cooling. At 390°C (* 5°) the direction of the curve changed sharply, with } C decreasing, indicating a rapid transformation to a non-ferro-magnetic phase. The X-ray photograph verified this conclusion. This result illustrates the use of magnetic measurements for phai boundary determinations„ 34. 300 e=I328 400 500 600 T F i g u r e 10s The paramagnetism of Cu 2 MnIn: The i n v e r s e of s u s c e p t i b i l i t y , 1/jC ( X i s measured i n ergs per gram per oe r s t ed ) , aga ins t temperature , T ( ° C , ) , 35. T(°C.) Figure l i s The paramagnetism of Cu2MnAl; The inverse of susceptibility, 1/x ( X i s measured i n ergs per gram per oersted), against temperature, T. 36. Figure 12: The paramagnetism of Cu3MnAl: The inverse of susceptibility, 1,6c ( X i s measured i n ergs per gram per oersted), against temperature, T. 37. Figure 13s The paramagnetism of Cu2MhSn; The inverse of susceptibility, 1/JC l s measured i n ergs per gram per oersted), against temperature, T. 38. V I I I . DISCUSSION OF RESULTS AND CONCLUSIONS 1, The s a t u r a t i o n magnetic moment a t abso lu te zero temperature f o r the purer specimen o f MnB used was 147 ergs per gram per o e r s t e d . T h i s r e s u l t may be as much as two percent l ow, because of the p o s s i b i l i t y o f a s m a l l amount of a second phase be ing p re sen t . The fe r romagne t ic Bohr magneton number was 1.73 jMB per MnB molecule (almost the same as the va lue f o r c o b a l t ) . T h i s va lue i s the same as t ha t c a l c u l a t e d f o r manganese when i t forms d s j r o c t a h e d r a l bonds. Al though o c t a h e d r a l bonds are not formed i n MnB (which has the same orthorhombic s t r u c t u r e as F e B ) , each manganese atom i s surrounded by fou r atoms a t 2.67A and two a t 2 .70A. Thus s i m i l a r bonding probably o c c u r s . The fe r romagnet ic C u r i e po in t of MnB was 309°G,-' as compared w i t h 1120°C f o r f ace -cen te red cub ic c o b a l t . The paramagnetism o f MnB f o l l o w e d the Cur ie -Weis s law c l o s e l y ; the paramagnetic Cur ie po in t was the same as the fe r romagnet ic one. 2 . The t e r n a r y a l l o y s i n v e s t i g a t e d con ta ined s e v e r a l f e r r o -magnetic t e r n a r y phases. Some which m e r i t f u r t h e r i n v e s t i g a t i o n a r e : (1) The 9 phases o c c u r r i n g i n the a l l o y s MnSnB and MnlnB. These phases, bes ides having the same s t r u c t u r e s and parameters as t i n and i n d i u m , had almost the same l i n e i n t e n s i t i e s on the x - r a y photographs. They were m a l l e a b l e , but r e t a i n e d t h e i r magnetism a f t e r c o l d w o r k i n g . (2) The cubic 0 phase of the Mn-Zn-B system, occurring for alloys with boron content of ten atomic percent. This phase was apparently ferromagnetic only i n the ordered state, and became disordered when cold worked. (3) The phase, of unknown structure, occurring i n the alloy Mn6Al3B-u. This phase had a lov; Curie point, since the magnetic moment per unit mass was more than three times greater at absolute zero than at room temperature. It was the only Mn-Al-B phase found with a Curie point near room temperature. The fact that there were no ferromagnetic phases like the ordered face-centered cubic Mn3XC phases (where X i s Al, Zn, Sn or In and carbon is i n the body-centered position) can be explained i n terms of size-factors. Hagg has found that, i n general, i n t e r s t i t i a l binary compounds have simple structures only i f the ratio of the atomic diameter of the small atom to that of the large atom i s less than 0,59, Thus iron and nitrogen, with a ratio of 0.56, sho'uld form a simple structure; they actually do, since Fe^N has the same structure as the Mn3XC phases, with nitrogen i n the body-centered position. This structure is unstable for Mn^C, since the ratio for manganese and carbon i s just at the c r i t i c a l value of 0.59. By re-placing some of the manganese atoms with larger atoms, the average diameter of the metallic atoms is increased. Thus the ratio of the carbon diameter to the metal diameter can be lowered below 0.59, creating the simple face-centered cubic structure, by the addition of only a small amount of another metal, X. Because the diameter of boron 40 is greater than that of carbon, the ratio for manganese and boron is increased to 0.67, and Mn^ B forms a complicated structure. Moreover, even i f enough larger metal atoms are used to produce the composition, MnaXB, the ratio will s t i l l be greater than 0.59 and the simple face-centered cubic structure will be unstable. The atomic diameters used for this discussion are: Element: Fe Mn In Sn Zn Al N C B Atomic Diameter: 2.48 2.6 3.24 3.02 2.66 2.86 1.40 1.54 1.74 T h e effect of boron on the alloys investigated might also be explained in terms of its electrochemical properties. Boron often occurs in rows or sheets in its allo7/s, and thus has a strong tendencjr to bond with itself. Therefore, since the interstitial atoms in the Mn3XC phases are as far separated from one another as possible, boron would not likely occupy such positions. 3. The results of the paramagnetic measurements on the Heusler alloys were inconclusive, because of the phase transformations and the loss of ordering at elevated temperatures. Most of the uncertainty was probably caused by the ordering effects. BIBLIOGRAPHY 41, 1. P. Weiss, Jour, Phys, (4), 6, 661. 2. C. Zener, Phys. Rev. 81, 440, 3. J. Slater, Phys. Rev. ;$6, 57. 4. H.P. Myers, Doctor of Philosophy Thesis, University of Sheffield, (1950). 5. G. Kidson, Masters Thesis, University of British Columbia, (1953). 6. F. Heusle'r, Zeit. f . Angew. Chem. 1£> 260. 7. B. Jassoneix, Compt. Rend. 142. 1336. 8. £. Wedekind, Ber. deut. Chem. Ges. 4JD, 1259. 9. H. Forestier and M. Graff, Compt. Rend. 203. 1006. 10. R. Hocart and M. Fallot, Compt. Rend. 203. 1062. 11.. R..Kiessling, Acta Chemica Scandinavia 146. 12.. W. Fink and L. Willey, American Soc. Metals Handbook, H 6 3 (1948), H. P h i l l i p s , J. Inst. Metals 6£, 275. 13... E. Potter and R. Huber, Trans. American Soc. Metals £1, 1001. 14. J. Schramm, Z. Metallkunde 3_2, 399. 15. H. Potter, Phil. Mag. (7), 12, 255. 16. C. Guillaud, Thesis, Strasbourg, 1 (1943). 17. H. Nowotny and K. Schubert, Naturwissenschaften }\» 582. 18. 0. Nial, Svensk Kern. Tid. 5J, 165. 19. U. Zwicker, Z. Metallkunde j j l , 399. 20. G. Shirokoff, Masters Thesis, University of Bri t i s h Columbia, (1953). 21. W. Goeddel and D. Yost, Phys. Rev. 82, 555. 


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