ELSEVIER Physica B 205 (1995) 421 423 PHYSICA Low temperature magnetic state of Ce(Feo.96Alo.04)2 compound A.K. Nigam a'*, S. Radha a, S.B. Roy b, Girish Chandra a a Low Temperature Physics, Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400005, India bCentrefor Advanced Technology, lndore 452 012, India Received 14 June 1994; revised 3 November 1994 Abstract Magnet•resistance(Ap/p)measurements•naCe(Fe•.96A••.•4)2c•mp•undinthetemperaturerange4.2 250 K andin magnetic fields up to 45 kOe are reported. The present study clearly suggests that in zero field, the low temperature state is an antiferromagnetic one, undergoing a metamagnetic transition to a ferromagnetic one in the temperature range 4.2 50 K at a characteristic field, (Hm) which decreases with increasing temperature. It has been observed that the substitution of Fe by even small concentrations of A1, Co or Ru brings in instability of ferromagnetism in the Laves phase compound CeFe2 [1,2]. In Ce(Fe, A1)2, the mag- netic susceptibility measurements show a second transition for A1 substitution below 5% at a tem- perature which is different but below the paramag- netic (PM)-ferromagnetic (FM) transition [2]. For AI concentration above 5%, susceptibility shows a single peak indicating paramagnetic to antifer- romagnetic (AF) [2] transition. The neutron scat- tering measurements on Ce(Fe, M)2 (M - A1, Co or Ru) indicate that the low temperature state of these compounds is an antiferromagnetic one [3]. In Ce(Fe, A1)2, the transition from FM to AF state is a gradual one, passing through a region of co- existence of FM and AF moments. A possibility of a spin canted phase in the coexistence regime has been suggested by non-linear susceptibility [4], neutron diffraction [3] and hyperfine field [5] measurements on the system. *Corresponding author. In the present study, the magnetoresistance (MR) measurements on Ce(Feo.96Alo.o4)2 are reported in the temperature range 4.2-250 K and in magnetic fields up to 45 kOe. The sample used for the present study has been used earlier for AC susceptibility and resistivity measurements [2]. The longitudinal MR was meas- ured using standard four probe DC technique. The electrical contacts to the sample were made with indium solder using ultrasonic soldering. The variation of (Ap/p) as a function of fields up to 45 kOe at different temperatures is shown in Fig. l(a) and (b). It is observed that for temper- atures between 4.2 and 50 K, magnetoresistance (Ap/p) is negligibly small (being less than 0.1% of the value at the maximum applied field of 45 kOe) up to a critical field Hm and then develops suddenly showing a negative contribution. In the present measurement, the largest change in (Ap/p) is of the order of 24%, observed at 50 K. The small (Ap/p) is indicative of an AF state and the development of a significant negative MR seems to be associated with a metamagnetic transition to a FM state. A similar transition in MR has earlier been observed 0921-4526/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSD10921-4526(94)00915-5