MAGNETIC AND M O S S B A U E R STUDY OF A M O R P H O U S Fe-Er-B RIBBONS
J. T E I L L E T t, H. LASSRI 2, R. K R I S H N A N 2 and A. L A G G O U N 1
i LP.C.M., INSA, B.P. 8, 76131 Mont-Saint-Aignan Cedex, France 2 Laboratoie de MagnOtisrne, 92195 Meudon Principal Cedex, France
Amorphous FesoErxBz0_,. ribbons (0 < x < 4) have been studied by magnetization mea- surements up to 16 Teslas and by M~ssbauer experiments under applied fields. At any temperature, magnetic saturation is attained for 4 Teslas. Higher fields do not break the Er-Fe magnetic coupling. Erbium sublattice has a cone spin structure and iron sublanice is probably close to eollinear.
1. Introduction
Metallic glasses based on transition metals and metalloids have been studied extensively. The influence of addition of various magnetic and non-magnetic atoms on the magnetic and transport properties has been well d o c u m e n t e d [1,2].
However studies on metallic glasses containing rare earth metals are very few [3].
We have reported recently on metallic glasses such as Fe-Er-B-Si [4] and Co-Er-B [5]. Another series, where B has been substituted by Er, has also been reported by us [6]. In this work, we describe magnetic and M6ssbauer studies on Fe80ErxB20_ ~.
In both cases, high magnetic field was applied to obtain some information on the anisotropy and spin structure.
2. Experimental
A m o r p h o u s Fe80Er.~B20_ x ribbons have been prepared by the usual melt-spin- ning technique under an inert atmosphere of argon. The a m o r p h o u s structure of the samples was verified by X-rays diffraction and their composition determined by electron probe microanalysis. Magnetization was measured in the temperature range 4 K to 290 K, under applied fields up to 16 Teslas in SNCI Grenoble. The Curie temperature T~ and the crystallization temperature were determined using a vibration sample magnetometer fitted with an oven. M 6 s s b a u e r spectra were obtained with a conventional triangular waveform spectrometer using a source of 5VCo in a rhodium matrix. Mossbauer experiments under applied fields were performed at the Francis Bitter National Magnet Laboratory, M.I.T., Cambridge.
M o s s b a u e r samples made of parallel ribbons were set perpendicular to the 3' beam.
9 J.C. Baltzer A.G. Scientific Publishing Company
Table 1
Compositions, crystallization and Curie temperatures
Compositions T x (K) T c (K)
Fe 79.5 Er0. 5 B20 683 645
F%0 Er 1 B19 727 628
F%0.1 Erl.TB18.2 765 585
Fe~0 Er2.TBlv.3 791 557
Feso.2 Er3. 8 B16 843 530
Magnetic studies
Table 1 summarizes the composition of the samples, their Curie T c and crystallization T x temperatures. The decrease in T c is due to the diminishing Fe content and hence Fe-Fe ferromagnetic exchange interactions. The increase in T x arises from the better stability of the a m o r p h o u s state b y the addition of Er, according to the good thermal stability of rare earth transition a m o r p h o u s alloys.
The field dependance of magnetization shows that saturation is attained only for H of about 5 Teslas at all temperatures. F o r H > 5 Teslas, one observes a small linear increase which also is reduced at 4.2 K. To obtain magnetization values, the linear part of o = f ( H ) has been extrapolated at H = 0. Figure 1 shows the concentration dependence of the magnetization o at 290 K and 4.2 K.
o decreases linearly at both temperatures with addition of Er. As the Fe concentration is constant, this decrease in o clearly arises from the antiferromag- netic interaction between Fe and Er moments. These m o m e n t s have been calcu- lated as follows. Though the addition of rare earth atom leads to a decrease in the transition metal (T.M.) m o m e n t due to hybridization effects, small concentrations of the former do not change the m o m e n t of T.M. Therefore the Fe m o m e n t /~F~
has been calculated from the Fes0B20 alloy magnetization and found to be 2.15 /t B. Then, the Er moment /SEt can be deduced from the relation ~ = ~ e ~ - /-ter
2 0 0
1 5 o
eJ
29 ;
IO0
I I I I
0 1 2 3 4
X(Er)
Fig. 1. Concentration dependence of a at 295 and 4.2 K,
where ~ is the alloy m o m e n t given by the magnetization measurements. For example for x = 1.7, one finds that /~Er = 8 ~ . This value, smaller than the theoretical value gJt~ B = 9 BB, would indicate the non collinearity in the Er spin structure, a p h e n o m e n o n which is well known for rare earths with strong random anisotropy and as we have shown in Co-Er-B-Si alloys [5]. The present results would show that the semi-cone angle is 26 ~ It is interesting to note that this value is much smaller than the value of 35 ~ found in Co-Er-Bi-Si alloys [5].
Therefore it is to be deduced that the random anisotropy of Er is smaller in Fe based alloys than in the Co based ones. N o w assuming /~Er--8 /~B for other compositions, calculated ;LEe is found to be practically the same, namely 2.12 + 0.02 ~B and hence independent of Er concentration in the range 0 to 4. This constancy could be explained as follows. Besides the small hybridization effects
~E 14(
120
Q O
O 0 0
o 0 0
D 0 9
o 9
~ 2
Q 6
BA ~
i m m " l0 m n m n m n
o m o 9
t O
9 4.2 K . 6 0 K o 1 0 0 K o 2 0 0 K . 2 7 5 K
I I I ~,
0 5 10 15
H O ' )
Fig. 2. High field dependence of magnetization in Fes0.2 Er3. s B16 at various temperatures.
arising from Er, /~ve is decreased by the charge transfer p h e n o m e n o n arising from B, as it was observed in Fe-B alloys [1]. As Er is replacing B in our alloys, the two effects would compensate and ~Fe remains the same even when Er increases.
Let us now examine the field dependance of the magnetization. Some typical results are shown in fig. 2 for x = 3.8 at different temperatures. The difficulty to reach saturation in these alloys arises basically from some canting of Fe spins.
Due to amorphous structure there is a distribution in Fe-Fe distances and competing interactions between ferro and antiferromagnetic a r r a n g e m e n t occur
1 . 0 0 .
0 . @ 8
|
I 1 . 0 0
0 . @ 5
- 1 o o ( M M / s ) : 0
T-
0 . @ 7
I I
- 9 o ( X L M / S ) @
1 . 0 0
I I
9 ~
I
