Separation of static and dynamic disorder in magnetic materials.

摘要

Conventional transmission Mossbauer, selective excitation double Mossbauer (SEDM), and zero-field muon spin relaxation (ZF-muSR) spectroscopy were used to identify static and dynamic magnetic disorder. With the construction of an efficient SEDM spectrometer, a consistent description of static magnetic disorder in an amorphous alloy (a-Fe80B 20) was developed using transmission Mossbauer and SEDM spectroscopy. Both methods measure the effects of the random static distribution of local magnetic environments around the Mossbauer nuclei. Magnetic fine particle systems (Fe3O4 ferrofluids, polysaccharide iron complex) were examined using transmission Mossbauer spectroscopy, and a model was developed that describes the entire range of dynamic magnetic behavior, from blocked moments on towards collective excitations and superparamagnetic moments. SEDM has measured 180° moment flips in the ferrofluids, determining a model independent relaxation rate of superparamagnetic moments. With the spectral signatures of static and dynamic magnetic phenomena identified, SEDM spectroscopy has been used to unambiguously verify the existence (a-Fe 92Zr8) and absence (Fe65Ni35) of magnetic relaxation in chemically disordered alloys. Additionally, the static and dynamic disorder in a magnetic fine particle system (a polysaccharide iron complex) and a frustrated magnet system (a-FexZr100- x), have been measured with ZF-muSR spectroscopy. The effects of collective excitations have been independently verified with ZF-muSR and moment fluctuation rates are in agreement with transmission Mossbauer spectra fit results. Two magnetic transitions have been identified with ZF-muSR in the a-FexZr100- x system, one at TC and another at Txy corresponding to transverse spin freezing, in both static and fluctuating magnetic components of muSR spectra. SEDM has been used to verify the existence of a fluctuation peak at T xy, and the time-dependent hyperfine interactions due to transverse spin freezing have been identified, where SEDM fluctuation rates are in agreement with ZFmuSR results.