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Preparation and magnetic properties of YbFe2, NdFe2, PrFe2
C. Meyer, F. Hartmann-Boutron, Y. Gros, B. Srour, J. Capponi
To cite this version:
C. Meyer, F. Hartmann-Boutron, Y. Gros, B. Srour, J. Capponi. Preparation and magnetic prop- erties of YbFe2, NdFe2, PrFe2. Journal de Physique Colloques, 1979, 40 (C5), pp.C5-191-C5-193.
�10.1051/jphyscol:1979570�. �jpa-00218987�
JOURNAL DE PHYSIQUE
CoIloque C5, supplkment au no 5, Tome 40, Mai 1979, page C5-191
Preparation and magnetic properties of YbFe,, NdFe,, PrFe,
C. Meyer. F. Hartmann-Boutron. Y. Gros. B. Srour
Laboratoire de Spectrometric Physique (*) B.P.
53X.
38041 Grenoble Cedex. Franceand J. J. Capponi
Laboratoire de Cristallographie du C.N.R.S., B.P. 166X. 38042 Grenoble
Cedex.
FranceRbumB.
- Nous dkcrivons la prkparation, A hautes pression
ettempkrature, des composks phase
deLaves YbFe,, NdFe, and PrFe,, ainsi que leur etude Mossbauer
al'aide
desisotopes FeS7
etYb170.
Abstract. - We
report
thepreparation under high pressure and temperature of the Laves phase compounds YbFe,, NdFe, and
PrFe,and their Mossbauer study with FeS7 and Ybl'O.
Until now there has been no study of YbFe,, NdFe, and PrFe, because they have only been successfully prepared once, and in impure form, by Cannon et al. [I]. By using high pressure and tempe- rature (80 kbars, 1 300 OC), we have succeeded in preparing samples of YbFe,, NdFe, and PrFe, which are good enough to allow magnetic and Moss- bauer measurements. We report here the main results already obtained.
YbFe,. - Its preparation was described in detail in [2] which also described the magnetic measurements and the Fe5' Mossbauer spectra. Since then the Yb1'@ Mossbauer study has been cpmpleted and will be published in detail in [3]. These experiments show that YbFe, is a ferrimagnet with a compensation temperature of 31 + 7 K. Below 50 K it is magne- tized along [I001
;above this temperature the magne-
Yanovsky recomputed
2500-
Fig.
1. - Hyperfine field of Ybl 'O inYbFe,.
Solid line and heavy dashed line : theory with pure exchangeonly.
Light dashed line : theory with the values of [4].tization seems to progressively deviate albeit slightly from [loo] but we are unable to identify its new direction ([u, v, 01, [u, u, w] ?). The hyperfine para- meters of Ybl7O cannot be fitted with the crystalline field and exchange parameters of [4] found for Yb17@
as an impurity in the isostructural compounds Tm,Ho, -,Fe, where crystalline electric field effects are large. Ifideed the crystalline electric field effects in YbFe, seem to be fairly small and we obtain good fits with pure exchange only (figure 1).
NdFe,.
-Some Mossbauer spectra of Fe57 in NdFe, are presented in figure 2. At low temperatures
(*) Laboratoire associk au C.N R S.
Fig. 2.
-
Fe5' Mossbauer spectra of NdFe,. Full curves are computer fits.Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979570
C5-192 C. MEYER, F. HARTMANN-BOUTRON, Y. GROS, B, SROUR AND J. J. CAPPONI
they exhibit a decomposition into two 2
:2 sub- spectra which is characteristic of a magnetization along [110]. This decomposition disappears rather abruptly around 160 K and there remains only three broadened lines. Computer analysis of the spectrum at 4.2 K leads to an average hyperfine field He,,
=190 kOe, to a dipolar splitting 2 A
=26 kG ( A is defined in [2]), and to a quadrupole coupling e2 qQ/2
=- 0.65 mm/s. A similar analysis can also be performed on the other spectra obtained below 150 K. Above 160 K we tentatively interpret the modification of the spectra as being due to a rotation of the magnetization from [I101 towards [I001
;at 300 K the computer fit leads to
and
cp =100
(angle with respect to [loo]). However above 160 K the fits are less good than below.
As shown in figure 3 the hyperfine field of NdFe, at 4.2 K, 190 kOe, lies much below the straight line drawn by Buschow ([5] figure 22) for the RFe, under
H (k-1 eff
Fig. 3. - Buschow's straight line.
true dipole effects for the ferromagnetic structure predicted to occur in the first half of the RFe, (0 kG)
;it could not either correspond to a ferrimagnetic structure (8 kG). Note that a similar, very large
((
dipolar splitting
Dis also observed in SmFe, in which it is practically temperature independent bet- ween 0 and 300 K ([5] Ref. 104). Possible explanations for this large splittingin NdFe, could be the following
:-
The RE moment have an antiferromagnetic structure. At low T this could indeed create a true dipolar splitting of the order of 20 kG. Such a struc- ture is however contrary to all current theories for the RFe,. In addition this explanation would not work for SmFe, since the Sm3+ moment is very small. Neutron diffraction experiments are planned in order to check the magnetic structure of NdFe,.
-
The hyperfine structure of the iron atom is anisotropic. If we assume that with respect to its local axis
(111
)it has axial symmetry
:and if we take account of the four inequivalent iron sites, we predict splittings of the Mossbauer spectra which are identical to those associated with true dipolar effects. This could explain the temperature independent splitting in SmFe,. If the disappearance of the splitting in NdFe, above 160 K is due to a rotation of the magnetization and not to the vanishing of
A ,this can be checked by applying a high magnetic field to a rigidly fixed powder
:we should observe a line broadening of the order 2 A . Mossbauer experiments in high field are planned in order to verify this.
the assumption that He,, contains a contribution
1
(g,- 1) J I coming from the RE Also the
<(dipolar splitting
>>2 A is much larger than that expected from
Fig. 4. - FeS7 Mossbauer spectra of PrFe,. Full curves are not ,theoretical fits.
PREPARATION AND MAGNETIC PROPERTIES OF YbFe,, NdFe,, PrFe, C5-I93
PrFe,. - As shown by figure 4 we have not yet positive quadrupole splitting which could correspond succeeded in preparing very pure products. At 4 K to tipping [6] associated with a huge
((dipolar split- the absence of substantial line broadening seems to ting
%.Here too Mossbauer experiments in high field suggest a [loo] magnetization direction. However the are planned. As in NdFe, the hyperfine field at 4.2 K spectrum is not Zeeman pure
:there is an apparent is 190 kG, also much below Buschow's straight line.
References
[I] CANNON, J. F., ROBERTSON, D. L., HALL, H. T., Mat. Res.
Bull. 7 (1972) 5.
[2] MEYER, C., SROUR, B., GROS, Y., HARTMANN-BOUTRON, F., CAPPONI, J. J., J. Physique 38 (1977) 1449.
[3] MEYER, C., GROS, Y., HARTMANN-BOUTRON, F., CAPPONI, J. J., (to be published).
141 YANOVSKY, R., BAUMINGER, E. R., LEVRON, D., NOWIK, I., O m , S., Solid State Commun. 17 (1975) 1511.
[5] BUSCHOW, K. H. J., Repts. Prog. Phys. 40 (1977) 1179.
[6] BOWDEN, G. J., J. Phys. F (Metal Phys.) 3 (1973) 2206.
