Magnetic properties of GdCo4−xFexB series studied by magnetostatic and Mössbauer effect methods

Journal of Magnetism and Magnetic Materials 104-107 (1992) 1437-1438 North-Holland

Magnetic properties of GdCO4_xFexB series studied by magnetostatic and M6ssbauer effect methods * Z. Drzazga, E. Popiel and A. Winiarska Institute of Physics, Silesian UniL~ersity,40-007 Katowice, Poland Magnetostatic and M6ssbauer studies were carried out on a series of GdCo 4 xFexB compounds with the hexagonal CeCoaB type structure (0 _
* This work was partly supported by Polish Ministry for Education in grant N B / 1 2 G / 1 F / 9 0 .

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Fig. 1. Variations of lattice constants a and c and the unit cell volume L. with iron concentration (x) for hexagonal structure of GdCo 4 xFexB.

the lattice c o n s t a n t a increases with x. For x > 1.5 this volume increases f u r t h e r with x b u t that increase is caused by the increasing of c o n s t a n t c. T h e m a g n e t o s t a t i c m e a s u r e m e n t s showed that all o b t a i n e d c o m p o u n d s were ferrimagnetically o r d e r e d with Curie t e m p e r a t u r e s (T c) h i g h e r t h a n 500 K. T h e t e m p e r a t u r e d e p e n d e n c e s of m a g n e t i z a t i o n for the G d C o 4 ~ F e x B c o m p o u n d s showed t h a t the c o m p e n s a tion t e m p e r a t u r e (Tcomo) d e c r e a s e d with increasing x (table 1). T h e m e a n m a g n e t i c m o m e n t of 3d atoms (P~3d) d e t e r m i n e d from m a g n e t i z a t i o n m e a s u r e m e n t s at 4.2 K increased with increasing of x, particularly for x >_ 1 (table 1). M e a s u r e m e n t s of magnetocrystalline anisotropy showed t h a t the c o n c e n t r a t i o n of Fe atoms

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1438

Z. Drzazga etaL I Magnetic properties of GdCo 4 ~Fe~ B

Table 1 The T~omp, #3d, and the easy direction of magnetizauon for the series of GdCo 4 ~FexB compounds X

Tcomp [K]

( ~ 3d ) [/XB]

0.00 0.10

~ 400 -

1.05 0.90

0.15

-

0.20 0.25 1.00 1.5(I 2.00 2.50 2.60

~ ~ ~ ~ ~

Easy direction at 293 K c c

0.8(1

370 300 280 200 195

c

1.05 0.90 1.17 1.35 1.45 1.50 1.50

~ • • • • ~

c c c c c c c

( x ) had a clear influence on the easy direction of magnetization [2,3]. M 6 s s b a u e r absorption spectra for G d C o 4 xFex B c o m p o u n d s with 0.1 _
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simple - only one sextet c o r r e s p o n d i n g to one lattice position occupied by Fe atoms. For x < 0.25 the spectra arc much more complicated - probably due to a r a n d o m occupation of the various lattice positions by Fe atoms. 2) 0.25 _ 2.0. In these spectra the d o m i n a n t contribution is the same as in previous samples but the hyperfine interactions of Fe atoms in these sites c h a n g e d (their q u a d r u p o l e interactions are distinctly weaker than in previous samples). Two o t h e r sextets are m o r e intense in these spectra. Shapes of spectra for samples x = 2.50 and 2.60 are almost the same and they are very similar to the c o r r e s p o n d i n g spectra from [5,7]. T h e s e M6ssbauer results are rather unusual and must be explained in the future. T h e s e are some problems with interpretation of results o b t a i n e d after standard fitting calculations of experimental M 6 s s b a u e r spectra for the samples with x = 0.10, 0.15 and 2.00 and it is a reason why in this p a p e r the exact numeric results for M6ssbauer experiments are not given. More exhaustive analysis of magnetostatic and M6ssbauer results should give m o r e detailed informations about the role of Fe atoms in the 3d-metal positions of this structure.

2oo

[mm/s]

Fig. 2. The M6ssbauer absorption spectra measured at 293 K for GdCo 4 xFexB compounds with 0.1 < x < 2.5. Solid lines represent the best fits.

References

[1] E. Burzo and N. Plugaru, Phys. Stat. Sol. (a) 113 (1989) K253. [2] N.M. Hong and J.J.M. Franse, J. de Phys. 49 (1988) C8-545. [3] Z. Drzazga and A. Winiarska, J. Magn. Magn. Mater. 83 (1990) 155. [4] Z. Drzazga, Physica B 168 (1991) 115. [5] P.P. Vaishnava and C.W. Kimball, J. Magn. Magn. Mater. 49 (1985) 286. [6] H.M. van Noort and D.B. de Mooij, J. Less-Common Met. 111 (19851 87. [7] G. Zouganelis and A. Kostikas, J. Magn. Magn. Mater. 75 (19881 9l. [8] Y.B. Kuzma and N.S. Bilonizhko, Sov. Phys. Crystal. 18 (19741 447.