Journal of Magnetism and Magnetic Materials 44 (1984) 279-286 279 North-Holland, Amsterdam LOW TEMPERATURE MAGNETIC HARDNESS OF MELT SPUN Fe-Zr AMORPHOUS ALLOYS D.A. READ, T. MOYO and G.C. HALLAM Department of Physics, University of leeds, Leeds LS2 9JT, UK Received 4 April 1984 Magnetic measurements have been made on iron-rich amorphous Fe-Zr alloys as a function of composition and temperature. We find no evidence of the spin-glass transition suggested by other workers, all our results being explicable in terms of an exponential increase in magnetic hardness on lowering the temperature. The magnetic hardness increases very rapidly with increasing Fe content. Both these results may be explained on the basis of compositionalinhomogeneityresulting in the presence of antiferromagneticinclusions, the volume fraction of which is assumed to govern the coercivity. 1. Introduction Anomalous low field behaviour of amorphous Fe-Zr alloys at low temperatures was first re- ported by Hiroyoshi and Fukamichi [1] for a sam- ple of composition Fe92Zr s. After cooling to 4.2 K in zero field, and subsequently applying a low field (< 0.04 T) they observed an initial rise in mag- netisation on increasing the temperature. At very low fields there is an abrupt increase in slope at ---30 K (T~). The magnetisation levels out fairly abruptly to a constant value above a field depen- dent temperature T h, which in a later paper [2] they redesignate as T t. On recooling in the field, this magnetisation was "frozen in", in a manner reminiscent of a spin-glass. In support of this interpretation they report asymmetry in the hyster- esis loops at helium temperatures. More recently, Hiroyoshi and Fukamichi [3] suggest the be- haviour they observe may be due to mictomag- netism, in view of the evidence of compositional inhomogeneity found by Yamamoto et al. [4] in their M(Sssbauer spectra, postulating the possible presence of an antiferromagnetic component. T e is tentatively suggested to be the ordering tempera- ture of antiferromagnetic iron, while T~ is regarded as a freezing temperature of antiferromagnetic clusters. The Invar-type behaviour of these alloys re- ported by Shirakawa, Ohnuma, Nose and Masumoto [5] also suggests the presence of an antiferromagnetic component. However, an analy- sis by Ghafari, Gonser and Wagner [6] of the field dependence of the MSssbauer spectrum for an alloy of composition Fe91Zr 9 failed to show any evidence of such a component. We have made measurements on a series of such alloys in the composition range FesgZrll to Fe93Zr7, prepared from argon-arc melted ingots by melt spinning in an inert atmosphere. The amorphous nature of the specimens was verified using X-ray diffraction. Although electron micro- graphs showed evidence of precipitation of micro- crystallites in some samples, the magnetic proper- ties did not appear to be affected, specimens from different production runs giving consistent results. 2. Low-field thermomagnetic effects Magnetisation measurements were made on roughly cylindrical specimens consisting of ~-7 mm lengths of ribbon packed into a 4 mm diam- eter hole in the specimen holder of a vibrating sample magnetometer (VSM). As shown in fig. 1, with the exception of the 89% specimen, we obtain results similar to those of Hiroyoshi et al. described above. However, on 0304-8853/84/$03.00 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)