Pergamon Solid State Communications, Vol. 98, No. 4, pp. 321-326, 1996 Copyright © 1996 Published by Elsevier Science Ltd Printed in Great Britain. All rights reserved 0038-1098/96 $12.00 + .00 S003S-1098(96)00042-7 AC Susceptibility Study Of Ce(Feo.9AIo.02 S. Mukherjee, R. Ranganathan Low Temperature Physics"Section, Saha hlstitute of Nuclear Physics, 1/AF Bidhannagar, Calcutta 700 064, bsdia S.B. Roy Low Temperature Physics Group, Centre for Advanced Technology, bldore 452012, hldia (Received 29 September 1995; accepted 5 January 1996 by C.N.R. Rao) Linear and non linear AC Susceptibilities have been experimentally investigated for Ce(Feo.9AI0.1)2. The results suggest that suppression of domain wall motion is responsible for the observed AC Susceptibility behaviour. The observed cusp in AC Susceptibility has nothing to do with the cusp observed in SG systems, eventhough there is a coexistence of ferromagnetic and antiferromagnetic phases with competing interactions in the present system. An attempt has been made to explain the different natures of the AC Susceptibility behaviours for different AI concentrations in the CeFe2 system by comparing with AI (4%) data. Introduction :- Anomalous behaviour of the Cubic Laves phase intermetallic compound CeM 2 (M = Fe, Co, Ni) in comparison with other RM 2 compounds ( R = Rare earth element) has been explained by 3d - 4f hybridization I CeFe~, extensively studied among the CeM 2 group is found to show ferromagnetism below T c - 230 K with a saturation magnetization of 2.3 la a per formula unit 2. Spin polarized calculations by Eriksson et al. predict spin moments on both Fe and Ce sites with the Ce moment (an almost equal mixture of 4f (-0.4 lat0 and 5d (-0.3 laB) contributions) aligned antiparallel to the Fe moment (1.43 law) 1. At 10 K the polarized neutron scattering results confirm their prediction with different values for magnetic moments 3. Neutron diffraction studies by Kennedy and Coles suggest a tendency towards AFM ordering even in the parent compound CeFe2 and the substitution of metallic impurities such as AI enhances this tendency. There are no contributions from the Ce moment in the ferromagnetic phase of Ce(Fel.xAIx) 2 with (x --- 0.02 - 0.08). Below x = 0.08, ferromagnetic order occurs in the compounds Ce(Fe~. ~AI~) 2. As we increase the AI concentration, To, i.e. the temperature at which the ferromagnetic component appears, decreases. However TN, i.e. the temperature at which the AFM component appears, increases. The overlapping region of two distinct magnetic phases results in the existence of a canted phase 4. A non-collinear arrangement of magnetic moments has been suggested to explain the magnetization behaviour of Ce(Fel.xAlx)2 5. For Ce(Feo.92A10.os)2, a region of canted phase characterized by the lack of saturation of magnetization and magnetoresistance even in an applied field of 5 T has been observed 6 Below x = 0.05 AC Susceptibility (ACS) and magnetization behaviour show features commonly observed in RSG systems. Macroscopic properties of many systems (RSG, Canted) with very different microscopic backgrounds may show some common features as their bulk properties are determined by some common mechanisms (e.g. pinning of domain wall motion), although the origin of these common mechanisms might be quite different. For AI (4*/,) these aspects have been discussed in detail from the linear as well as nonlinear ac susceptibility point of view 7. For AI (10%) a preliminary measurement of AC Susceptibility has been reported 8 We wish to emphasize that the general nature of the AC Susceptibility curve is very different from that obtained for AI (4%). But the origin of this nature in the context of increasing A1 concentration in Ce(Fei.xAl~) z has not been very clear although it is very important for a clear understanding of the system from the nmcrascopic point of view. This motivates us to investigate the system in detail from linear as well as nonlinear ACS point of view under different experimental conditions (i.e. z(hac, co, HDc)). Regarding nonlinear studies it has been found that for AI (4%) the nonlinear ACS behaviour is similar to that observed in SG/RSG systems even though AI (4%) is a canted system. We have extended 321