Nd - Fe - Al, A SPIN GLASS TRANSITION IN A COLLECTION OF SUPERPARAMAGNETIC CLUSTERS.
In the Nd-Fe-A1 system, compositions in the range of Nd{sub 60}Fe{sub 30}Al{sub 10} have been reported to be ferromagnetic bulk metallic glasses with high coercivities. Careful examination of both the microstructure and magnetic properties of these materials shows this to be true only in the most general sense. The materials are shown to be nanocomposites, in the strictest sense, with characteristic structural length scales on the order of 1.2 nm. Magnetically, the materials are also composites exhibiting a number of magnetic transitions as a function of temperature. The temperature dependence of the magnetic properties will be discussed in terms of strongly-interacting superparamagnetic clusters residing in a paramagnetic matrix. The clusters exhibit a frequency-dependent blocking temperature as determined from AC susceptibility, that is inconsistent with simple superparamagnetic behavior but is consistent with a spin glass-type ordering of the clusters to form a cluster glass. For a temperature region extending approximately 100 K below the cluster glass ordering temperature, the materials exhibit low coercivity. Below this temperature regime significant coercivities develop. The energy barrier to magnetic reversal provided by the product of the cluster volume multiplied by the anisotropy energy is inconsistent with the values required to fit the superparamagnetic behavior above the spin glass transition in the framework of the random anisotropy model. Instead, the existence in this system of significant coercivity is associated with a change in the paramagnetic fraction of the sample consistent with antiferromagnetic ordering of part of the paramagnetic matrix. The remainder of the matrix material orders ferromagnetically at a lower temperature and the interaction between the antiferromagnetic clusters and the ferromagnetic matrix underlies the large coercivities observed at low temperatures.
- Research Organization:
- BROOKHAVEN NATIONAL LABORATORY (US)
- Sponsoring Organization:
- USDOE Office of Energy Research (ER) (US)
- DOE Contract Number:
- AC02-98CH10886
- OSTI ID:
- 15006570
- Report Number(s):
- BNL-71067-2003-CP; R&D Project: MA410MABA; KC0202020; TRN: US200411%%350
- Resource Relation:
- Conference: 17TH ANNUAL WORKSHOP ON RARE EARTH MAGNETS, NEWARK, DE (US), 08/18/2002--08/22/2002; Other Information: PBD: 18 Aug 2002
- Country of Publication:
- United States
- Language:
- English
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