416 Journal of Magnetism and Magnetic Materials 70 (1987) 416 418 North-Holland, Amsterdam HIGH FIELD MAGNETIZATION MEASUREMENTS ON Tb2Fel4B AND Er2Fet4B SINGLE CRYSTALS J.P, GAVIGAN, D. GIVORD, H.S. LI, O. YAMADA *, H. MARUYAMA * M. SAGAWA and S. HIROSAWA t Lahoratoire Louis No'eL ('.N.R.S., 160 X, 38042 Grenoble cede.v, f'rance • Department of Phystcs. Faculty of Science. Okayama Utlit!ersitv. 3-1 l 7~'ushtma-Naka. Ot,avama 700. Japan + Sumitomo Special meta/~" ('o.. Ltd.. Egawa. Shimamotocho Mt.s'hima.gun. Osaka 61& Japan High field magnetization measurements between 4.2 and 275 K have been performed on single crystals of Tb2F%4B and ErzFel4B. The results obtained have been accounted for by' a set of exchange and crystal field parameters. The laner were obtained by a direct scaling from values obtained in a detailed stud\, of NdeFelaB. 1. Introduction Since the discovery of the R2F%4B family of compounds, many studies concerning high field magnetization measurements on single crystals have been reported [1--5]. In particular, a detailed study of the NdeFeHB compound [5], permitted the deduction of a com- plete set of crystal field parameters. The set of parameters {A ..... } which represents the crystal field environment acting at a given rare earth site are listed in table 1. In this paper we report high field magnetization measurements for Tb2F%4B and Er 2 Fe~4 B compounds and compare the results to calculated behaviour using this set of A ..... parameters. 2. Results The single crystals were prepared using the floating zone melting technique [3]. The high field measurements were performed in the S.N.C.I. at the C.N.R.S., Grenoble. The magnetic fields of up to 19 T were provided by a Bitter coil. Examples of the magnetization curves obtained are shown in fig. 1 (Tb2Fel4B) and 2 (Er2F%4B) for T-4.2, 150, 275 K. In Tb2F%4B the easy axis over the whole tem- perature range is [001]. Although the results do not reveal much basal plane anisotropy, [110] is found to be easier than [100]. In Er2Fe~4B the magnetization lies in the basal plane at low tem- peratures with [100] being easy. A magnetization reorientation towards the [001] axis occurs at T= 323 K in agreement with previously reported val- ues [2,3]. The temperature dependence of the spontaneous magnetization for each of the con> pounds is presented in fig. ld and 2d. 3. Discussion The results were analysed according to the method described in ref. [5]. The system is de- scribed by' the 2 coupled equations: ,Z G = E &,,,O,,,,,- (nkt,.(M..~> + B~,,,,, ). (M~>, ptm /:', ~ = KI sin20 -- (n!~,~~,, M.~ )/-- + B~,pp) - (M~,.) , which, respectively, determine the state of the rare earth and iron moments. In these equations the different parameters have their usual meaning. n~m,, is the molecular field coefficient which de- scribes magnetic interactions between R and Fe moments in the ferrimagnetic state [6,7]. The B..... are related to the A ..... by: O,,(r")A ..... (1 -o,)[8]. In the analysis of the data, B..... values for each of the compounds were deduced from the values of A ..... given in table l. nRv" was determined by fitting the experimental temperature dependence of the spontaneous magnetization, where the ten> perature dependence of the Fe sublattice magneti- zation normalized to its absolute saturation value was assumed to be identical with that of Y:FeI4B (figs. ld and 2d) [11. The values obtained were 147/,~ and 144/, o for the Tb and Er compound, 0304-8853/87/$03.50 ~". Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)