A first order phase transition induced by magnetic field and temperature

Taking the pseudobinary C15-Laves phase compound Ce(Fe 0.96 Al 0.04) 2 as a paradigm for studying a ferromagnetic(FM) to antiferromagnetic(AFM) phase transition, we present interesting thermomagnetic history effects in magnetotransport measurements across this FM-AFM transition. We argue that these distinctive hysteretic features can be used to identify the exact nature first order or second order-of this kind of transition in magnetic systems where electrical transport is strongly correlated with the underlying magnetic order. A comparison is made with the similar FM-AFM transitions observed in Nd and Pr-based manganese compounds with perovskite-type structure. 1 The nature of ferromagnetic (FM) to antiferromagentic (AFM) transition in the perovskite-type manganese oxide compounds Nd 1/2 Sr 1/2 MnO 3 and Pr 1/2 Sr 1/2 MnO 3 has been the subject of close scrutiny in recent years [1,2]. The FM-AFM transition observed in these compounds is taken as a sort of a prototype of a first order transition, and certain ther-momagnetic features have been highlighted which are thought to be generic of a first order phase transition [1,2]. In the same spirit we have undertaken a study of FM-AFM phase transition in the pseudobinary C15-Laves phase compound Ce(Fe 0.96 Al 0.04) 2. We find striking thermomagnetic history effects in magnetotransport measurements across the FM-AFM transition in this interesting system. CeFe 2 , with its relatively low Curie temperature (T C ≈230K) and reduced magnetic moment (≈ 2.3µ B /f.u.) [3], is on the verge of a magnetic instability [4]. Neutron measurement has shown the presence of antiferromagnetic fluctuations in the FM ordered state of CeFe 2 below 100K [5]. With small but suitable change in electronic structure caused by doping with elements like Co, Al, Ru, Ir, Os and Re at the Fe-site of CeFe 2 [6], these antiferromagnetic fluctuations get stabilized into a low temperature AFM state, and after certain concentration of dopants (usually 5 to 10%) this AFM phase replaces the FM phase altogether [7–14]. While most recent experimental efforts are mainly focussed on understanding the cause of this magnetic instability [15,16] in CeFe 2 , there exists one other aspect of the observed magnetic properties which needs proper attention, viz. the exact nature of the FM-AFM transition. We have recently addressed this second question in Ru and Ir-doped CeFe 2 alloys [17,18]. In this paper we shall focus on the Al-doped CeFe 2 alloys. In contrast to the Ru, Co and Ir doped …