EASY DIRECTION OF MAGNETIZATION IN GdFe2

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EASY DIRECTION OF MAGNETIZATION IN GdFe2

T. Mizoguchi, Y. Tanaka, T. Tsuchida, Y. Nakamura

To cite this version:

T. Mizoguchi, Y. Tanaka, T. Tsuchida, Y. Nakamura. EASY DIRECTION OF MAGNETIZATION IN GdFe2. Journal de Physique Colloques, 1979, 40 (C2), pp.C2-211-C2-212. �10.1051/jphyscol:1979275�.

�jpa-00218673�

JOURNAL DE PHYSIQUE Colloque Cl, supplément au n" 3, Tome 40, mars 1979, page C2-211

EASY DIRECTION OF MAGNETIZATION IN G d F e2

T. Mizoguchi, Y. Tanaka*, T. Tsuchida and Y. Nakamura

Department of Metal Soienoe and Technology, Kyoto University, Kyoto 60S, Japan

Résumé.- La direction de facile aimantation de GdFe2 a été déterminée par spectromëtrie Mossbauer

du 5 7Fe. L'anisotropie est si faible que les impuretés de terres rares contenues dans Gd jouent le

rôle le plus important.

Abstract.- The easy direction of magnetization in GdFe2 has been investigated by using the 57Fe Mossbauer effect. The anisotropy in GdFe2 is so weak that some of the rare-earth impurities invol- ved in Gd metals play an important role in determining the easy direction of magnetization in GdFe2.

Recently Mossbauer effect measurements of

57Fe have been used for the determination of the easy direction of magnetization in polycrystalline magnetic materials containing Fe, including the intermetallic compounds with the cubic Laves struc- ture RFe2 where R is a rare-earth element. In this structure the principal axis of the electric field gradient is parallel to jj lTJ and all iron sites are crystallographically equivalent in a paramagnet- ic state. Even in a magnetic state, if the easy direction of magnetization is [jOCf] , all the iron sites are still equivalent. However, if the easy di- rection is along either [j 1 jQ o r D'3 ' w e n a v e

two magnetically inequivalent iron sites and the Mossbauer spectrum consists of a superposition of two six-line patterns with the intensity ratio with either 1:3 or 2:2.

The first experiment of GdFe2 was done by Bowden et al. /]/, The spectrum obtained at 77 K was complicated, suggesting that the easy direction of magnetization lies along neither JjOO] , D'?]

nor 0 ' Q • However, Atzmony and Dariel /2/ report- ed a single six-line pattern, indicating the Q o o ] easy direction, whereas the £j10] easy direction has been proposed by Barb et al. /3/ who observed a spectrum consisting of two sets of six-lines with equal intensity at 77 K.

In order to remove the discrepancies between these results and to find the easy direction of mag- netization. in GdFe2, we have prepared samples of GdFe2 giving attention to the following points;

1) the effect due to the amount of excess Gd metals, 2) the effect of the difference in heat treatments

and 3) the effect of impurities in the Gd metal ingot on the Mossbauer pattern.

Mossbauer effect measurements of 57Fe for sev- eral GdFe2 samples indicate that the Mossbauer pattern is determined mainly by the quality of the starting Gd metal ingot and that the amount of excess Gd metal and the condition of the heat treat- ment give almost no effect on the Mossbauer pattern.

We obtained completely different spectra for two GdFe2 samples made of two different Gd metal ingots stated to be of 99.9 % purity. One spectrum obtained from GdFe2 made of Gd(A) metal ingot is in good agreement with that reported by Barb et al. The other spectrum obtained from GdFe2 made of a Gd(B) metal ingot, however, is similar to that obtained by Bowden et al. These results suggest that the discrepancies between the measurements reported by several authors may be due to the impurities in the starting Gd metal ingot. The results of chemical analysis of the two Gd metal ingots are given in table I, which shows that the Gd(A) metal ingot con- tains a surprisingly large amount of Nd of 2.2 %.

In order to clarify the influence of rare- earth impurities, we have prepared samples of GdFe2 made of the Gd(C) metal with higher purity (see Table I) and added a small amount of a rare-earth impurity. Mossbauer effect measurements indicate that the easy direction of (Gd.Nd)Fe2 is jj1(H> a s

shown in figure 1 (a), and it is clear that the Nd impurity induces the [jio] easy direction. On the other hand, the easy directions of (Gd.Er)Fe2 and

(Gd.Dy)Fe2 are found to be [j 1FJ and JjOO], respec- tively, as shown in figure 1 (b) and figure 1 (c).

These experiments indicate that the anisotropy of GdFe2is small and that the rare-earth impurities play a decisive role in determining the easy direc- Present address : Research and Development labora-

tory, Matsushita Electric works, Ltd., Kadoma, Osaka 571, Japan.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979275

c2-2 12 JOURNAL DE PHYSIQUE tion of magnetization in GdFe2. Figure I (d) shows

the Mossbauer pattern of the pure GdFen made of

Table I

Gd(C) which is the most reliable ~Essbauer spectrum Chemical analysis of Gd metals (ppm) of GdFen and it is quite similar to that obtained by

Bowden et al. Therefore, the easy direction of ma- gnetization in GdFe2 can not be determined straight- forwardly as one of the

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References

/ I / Bowden, G.J., Bunbury, D.Stp., Guimaraes, A.P., and Snyder, R.E., J. Phys. C1 (1968) 1376.

/ 2 / Atzmony, U., and Dariel, M.P., Phys. Rev.

(1974) 2060.

/ 3 / Barb, D., Burzo, E., and Morariu, M., J. Physi- que Colloq.

2

(1974) C6-625.

Fig. I : Mossbauer spectrum at 77 K for GdFez made of Gd(C) metals. (a) : added Nd metals as an impu- rity; (b) added Er metals as an impurity; (c) : added Dy metals as an impurity; (d) : pure GdFez.