Solid State Communications,
Vol. 77, No. 8, pp. 567-569, 1991. 0038-1098/91$3.00+.00
Printed in Great Britain. Peqamon Press plc
MAGNBTIWTIGN STUDIBS IN Co-Ho-B AMORPHOUS ALLOYS R. Krishnan, 0. Bl Marrakchi and II. Lassri
Laboratoire de Mag&isme, C.N.R.S. 92 195 Meudon cedex, France (Received 13 november 1990 by P. Burlet)
ABSTRACT
Amorphous Co80_z I$ B20 alloys have been prepared by melt spinning technique and their magnetization measured in applied fields up to 80 kGe. The saturation is obtained for H < 30 kGe at all temperatures.
The projection of the Ho moment at 4 K is found to be 10.2 & 0.5 j#B in agreement with the theroretical value. This would indicate a collinear spin structure for Ho unlike for Br. It can be concluded that the
idf~tOtIMgm?tiC in~pction J&-HO
iS
SlfOngetthan the random
anisotropy. For x= 11.5 at 4 K, the Ho sub-network moment dominates.
INTRODUCTION
Melt quenched amorphous alloys containing rare earth (RI?) atoms are of interest both from fundamental and practical points of view and are of current interest I-3. For the RE atoms with spin orbit interaction one generally observes random anisotropy 4. We have recently reported some interesting results on the spin structure and the high field magnetization behaviour of Er, which has a large random anisotropy 5a6. In this note we
fields close to 30 kGe at all temperatures. The magnetization (M in emu.g-l1 at 295 K is shown in Fig. 1 as a function d Ho content. Also are shown for comparison our data for RC Er 5 and Gd ‘. I1 is seen that the magnelizalion decreases inilialiy almost linearly with increasing Ho content. This decrease in M is essentially due to the antiparallel coupling between Ho and Co moments. This decrease in M is similar to that of Er bul less slronger than in the case of Gd. Though the magnetic momenl of Gd is smaller than that of’
Howish to describe our magnetization studies in a-Co-Ho-B alloys and compare the results with
those on Er.
150 T.29SKEXPERIMENTAL DETAILS
,M Amorphous C~rr,l_~ IIo, Bzc ribbons with 0 5 z I 2 12 were prepared by me11 spinning technique
using a sin8le roller and in an argon atmosphere. ; The amorphous slate was checked by z-ray
diffraction. The composition of the alloys were 50- determined by electron probe micro analysis. The
magnetization was ,measured in applied fields up to 80 kGe and we shall discuss here only results
at 4 and 295 E and compare them with our
cd0 1 I
previous results on Er and Gd.
0 !I 10 1sX RESULTS AND DISCUSSIONS
Fig. I The RE I Ho, Er, Gd 1 concentration The magnetization (MI begins lo saturale for dependence of the magnetiation at 295 K.
567
568
MAGNETIZATION STUDIESal 4 K. as we shall see later. this stronger decrease in M observed for Gd is due to the higher thermal stability of the Gd sub-net work moment In order to evaluate the Ho moment let us examine the results at 4 K. Fig. 2 shows the field dependence of the magnetization for three different Ho concentrations. It is seen that M saturates for H of about 30 kOe and for higher fields a small susceptibility is seen. The horizontal part of the curve was extrapolated to obtain
Mat H-O. The moment of Ho was determined as follows. It is known that with the addition of rare earth metal, the transition metal moment decreases due to hybridisation of the 5d and 3d orbitals. However as we have shown before for the case of Er 5, such a decrease in Co moment is negligible for x i 5. So for I - 3.6, the Co moment can been taken as 1.25 )“B a value which was obtained for the sample with I - 0. So knowing the alloy momenl MA, the projection of the Ho moment )“Ho along the applied field can be calculated from the relation 1 )1AI - 1 Jlco - )lljol and it is found to be 10.2 t 0.5 )“B. This value agrees with the theoretical value
igJ) - 10)~and close to the experimental value oflO. MB found in the literature *. This would indicate that lhe Ho spin structure is collinear in the first approximation. This result shows that the random antsotropy of Ho is rather small, allhough the ground slate of trivalent Ho is ‘1s with a spin orbit coupling. The fact that the samples need a field of about 30 kOe (the field is applied in the ribbon plane) to saturate shows that some
)-
B-
3- 0
T.4.2K
. , . . . .
x.1. ..I . .
10 20 30 40 30 00 70 50
H(kOe)
Fig. 2 The field dependence of the magnetization in a-Co-Ho-B alloys at 4 K.
IN Co-Ho-B AMORPHOUS ALLOYS
Vol. 77, No: 8 anisotropy is however present.
11can be concluded that the anliferromagnelic inleraction Jco-ho is therefore stronger than the random anisotropy and it keeps the moments antiparallel.
It is interesting to recall here that in Co-Er-B alloys the Er spin structure was found to be conical with a large average cone angle of about 82’ and which we had attributed to the strong random anisotropy of Er 5.
Now assuming our experimental value of )1Ho it is possible to calculate back the values of flCo for the other compositions. As shown in Fig. 3, it is found that pCo decreases for x ) 5 PS found by us also in the case of Er 5. The variation of the alloy moment (PA) as a function of Ho content is also shown in Fig. 3 It can be seen that the magnetic compensation occurs for x close lo 8 and in the alloy with x = 11.5, at 4 K, it is the Ho subnet-work moment which dominates. The results for Er and Gd are also shown in Fig. 3 for comparison. The concentration of RE needed for the compensation is found to be smallest for Ho in accordance with its highest moment.
Measurements are in progress under higher fields up to 200 k Oe to see whether the antiferromagnetic coupling between Co and Ho moments could be broken as was found 5 in the case of Er and will be reported in the luture.
The analysis of the composition by Mme.
Dumond is greatfully acknowledged. The high field measurements were carried out at Service National des Champs Intenses, Grenoble.
1.5
T.4.2K . Cd
I . Er
Fig. 3 The RE (Ho. Er, Gd) concentralion
dependence of the alloy moment and that of pCo
on.the Ho content at 4 K.
Vd. 77, No. 8 MAGNETIZATION STUDIES IN Co-Ho-B AMORPHOUS ALLOYS 569
