Anomalous Nernst effect in perovskite La0.5Ca0.5CoO3

Abstract

Anomalous Nernst effect (ANE) has drawn special attention during the last few years because of its possibility in thermal energy harvesting and fundamental physics involved [1]. Reports on ANE in perovskite oxides are relatively few compared to ferromagnetic metallic alloys. The ANE was previously reported in Sr substituted LaCoO3 [2]. Because of the smaller size of Ca2+ cation compared to Sr2+, magnetic interactions are expected to be modified. Hence, we studied the ANE in La0.5Ca0.5CoO3 for the first time, which shows ferromagnetic ordering at 147 K (Fig. 1(a)). The non-saturating nature of the field dependence of magnetization and its smaller value shown in the inset of Fig. 1(a) indicates the existence of competitive FM-AFM interactions that largely depends on the spin states of the Co3+ and Co4+ ions[2-4]. Such a system can be very interesting to study ANE as the aforementioned competitive effect may dramatically affect the spin-dependent deflection of thermally driven charge carriers. The presence of the ANE in La0.5Ca0.5CoO3 is confirmed from the field dependences of the Nernst thermopower (Sxy) as shown in Fig. 1(b), which shows hysteresis like the magnetization. In this preliminary work, we have carried out ANE measurements only at four selected temperatures. Sxy nearly saturates above 20 kOe at 40 K but not at 100 K, where it has a maximum value at the highest field. The Sxy shows behavior similar to superparamagnetic at 160 K and linear behavior at 200 K with much-reduced values. Magnetic, electrical transport, thermoelectric measurements, and ANE at multiple temperatures will be carried out to realize the mutual effects of magnetism, charge, and heat currents to establish a better relationship between them.This work was supported by the Ministry of Education, Singapore (Grant no. R144-000-422-114 and R144-000-442-114).  Fig. 1: (a) Temperature dependence of magnetization (M) in La0.5Ca0.5CoO3 . Inset: Field dependence of (b) M at 5 K. and (b) Nernst thermopower (Sxy) measured at T = 40, 100, 160 and 200 K.