Magnetic Interactions in Rare-Earth — 3d Intermetallics

Abstract

In the scope of the CEAM project progress has been made in the following subjects:

• preparation, especially single crystal growth,

• study of magnetization processes in magnetic fields up to 40 T,

• evaluation of the experimental results by developing a theoretical framework.

At the start of the CEAM project, the production of single crystals was mainly focussed on the R₂T₁₇ compounds (T-Fe, Co). A series of thirteen sizable single crystals has been prepared with volumes of the order of 1 cm³. High-magnetic-field studies revealed a new type of exchange driven magnetic transition in fields above 20T. These transitions can succesfully be described by a model involving the exchange and crystal field interactions. The values for the interaction parameters as derived from magnetisation measurements have been checked by inelastic neutron diffraction studies at the Institut Laue Langevin in Grenoble on a large single-crystalline sample of Dy₂Co₁₇. The potency of the model is shown by the applicability to other series of RE-3d intermetallics. At the same time, field-oriented powders of polycrystalline RE₂Fe₁₄B and RE₂Co₁₄B compounds were studied in order to establish the magnetic parameters of both series. The production of high-quality single crystals of the 2:14:B series turned out to be less trivial than in case of the 2:17 compounds and the pulling rate in the Czochralski technique had to be reduced by a factor of ten (3 mm/hour). Sizable single crystals of the 2:14:B series have been produced for Y₂Fe₁₄B, Nd₂Fe₁₄B, Gd₂Fe₁₄B, Tb₂Fe₁₄B, Dy₂Fe₁₄B and Nd₂(Fe_0.8Co_0.2)₁₄B. These samples have been investigated in high magnetic fields and, on the basis of these results, values for the exchange and crystal-field parameters have been deduced for both series. A new technique has been developed for measuring the exchange stiffness between the rareearth and 3d sublattices by performing long-pulse high-field measurements on free powders. Finally, an extensive study has been started in order to determine the individual site contributions to the anisotropy of the 3d sublattice in several series of Y-(Fe,Co) compounds, in particular in the Y₂(Fe,Co)₁₄B pseudo-ternaries.