Magnetische untersuchungen an ternären SE (Fe, Al)2 laves-phasen (SE = Y, Gd. Dy, Ho)

Chapter 48 Crystal structures and crystal chemistry of ternary rare earth-transition metal borides silicides and homologues

The magnetic properties of the Laves phase series Gd(Fe1-xAlx)2 have been studied by means of magnetisation measurements in fields up to 160 kOe for 0 or=0.8. The mean magnetic moment increases almost linearly from GdFe2 to GdAl2. This implies a constant iron moment for all iron atoms throughout the whole concentration range. The Gd atoms appear to be the magnetising element of the diluted Al-Fe matrix.

On the magnetic properties of Gd(Fe1-xAlx)2 compounds

The structural behavior and phase relationships of materials in the composition range DyFe3-Dy2Fe17 with Al substitution for Fe have been investigated in alloys which have been given various heat treatments. The binary phases DyFe3 (PuNi3-type), Dy6Fe23 (Th6Mn23-type) and Dy2Fe17 (Th2Zn17type) have been confirmed. Phase boundaries on Al substitution for Fe in these compounds in as-melted materials are Dy0.25Fe0.70A10.05, Dy0.027Fe0.593A10.20 and Dy0.105Fe0.745Al0.15. For Dy0.25Fe0.75−xA1x with x = 0.175−0.30 the CeNi3 type is observed with indications of a statistical distribution of Fe and Al on the transition metal sites. For x = 0.70 the Au3Cu type is found when materials are annealed at 1000 °C. Around a composition Dy0.105Fe0.695A10.20, in both as-melted and annealed (800 °C) specimens, a new structural type is observed with an a axis corresponding to the Th2Ni17 type but with a c axis only half as long. This new structure is derived from the Th2Ni17 type by disordered substitutions. The Th2Zn17-type structure is stable from x = 0.25 to x = 0.60 in as-melted Dy0.105Fe0.895−xA1x material.

Studies on compounds DyFe3, Dy6Fe23 and Dy2Fe17 with al substitution for Fe I: Structural investigations

Crystallographically partly randomized materials with high magnetic anisotropy exhibit anisotropy and exchange fluctuations. Possibly the most dramatic consequence of these interaction fluctuations is the presence of giant intrinsic magnetic hardness observed, especially at cryogenic temperatures. This magnetic hardness (resistance to demagnetization) is anintrinsic solid state property, quite in contrast with hardness in technologically important materials based on the presence of fine particles or precipitate phases. It introduces rather a further variety in the phenomenology of interaction fluctuation materials such as spin glasses, representing the extreme case of high anisotropy and high moment concentrations. In this paper the phenomenon of strong intrinsic magnetic hardness is reviewed, and some new experimental data are presented for homogeneous pseudobinary regions of composition on the basis of such compounds as SmNi5, SmCu5, SmCo5, TbFe2 and others. Magnetic hardness in some of these cases reaches the highest values found so far for any class of materials. For instance, maximum values of coercive force of aboutH
 c=230 kOe are observed for SmCo5−xNix. Even higher values are extrapolated in other cases. Maximum values ofH
 c are observed in materials with ordering temperatures of order 60–200 K. A strong temperature and a weaker time dependence ofH
 c is observed and discussed on the basis of theories involving thermal activation of domain propagation. Comparisons are drawn with effects generally observed in magnetically hard materials, and the relationship of intrinsic magnetic hardness to technologically interesting materials is discussed. Tentative conclusions as to the details of the origins of giant intrinsic magnetic hardness are drawn and areas of future interest are indicated.

R. Grössinger

Papers

Magnetic investigations on Dy(FexAl1-x)2 laves phase compounds