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A Pulsed N.M.R. study of the ferromagnets Ni, Fe₂P and Fe₃P

University of British Columbia

The pulsed N.M.R. technique has been used to study the ferromagnets Ni, Fe₂P and Fe₃P. The dependence of the N.M.R. free induction decay on the strength of the applied r.f. field and on pulse length has been studied in nickel powder. The results indicate that the applied r.f. field is enhanced and that there is a distribution of enhancement factors. The distribution can be explained in the light of a model in which the domain walls vibrate like pinned membranes. The maximum enhancement factor is estimated to be 4700. The N.M.R. of ³¹P and ⁵⁷Fe has been observed in Fe₂P. Zero field resonances have been observed at the frequencies 17.5 MHz, 20.5 MHz, 77.5 MHz and 86.6 MHz at 1.5 K. These results allowed the deduction of the hyperfine fields at the various atomic sites. These are H[sub n] (FeI)=148 koe., H[sub n] (FeII)= 123 koe., H[sub n] (PI)=50.2 koe. and H[sub n] (PII)=45.0 koe.. From the shift of the N.M.R. frequency on application of an external magnetic field the sign of the phosphorous hyperfine fields is shown to be positive. The temperature dependence of the ³¹P N.M.R. frequency has also been studied and the data is well 2 fxtted by a T² law. Domain wall enhancement of the applied r.f. field was studied in the light of the pinned membrane model. Studies of the nuclear relaxation times indicate that thermal fluctuations of the domain walls provide the dominant relaxation mechanism. In Fe₃P a rather complicated N.M.R; spectrum was observed. Resonances occur at 41.7 MHz, 37.2 MHz, 34.5 MHz, 27.5 MHz and 24.8 MHz. These are all attributed to iron sites and correspond to hyperfine fields of 304 koe., 271 koe., 200 koe., and 180. koe. . Domain wall enhancements were also studied in the light of the pinned membrane model. Nuclear relaxation times were also determined and the results indicate that thermal fluctuations of the domain walls provide the dominant relaxation mechanism.

Text

2011-03-22

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http://hdl.handle.net/2429/32726

Physics

University of British Columbia

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