Complex magnetism and magneto-transport of RECoPO (RE = La, Nd, and Sm)

Abstract

We report the electrical, magnetotransport, and specific heat of the layered polycrystalline RECoPO (RE = La, Nd, and Sm) samples. These compounds are iso-structural to recently discovered superconductor LaFeAs(O/F). Bulk polycrystalline samples are synthesized by a solid state reaction route in an evacuated sealed quartz tube. All these compounds are crystallized in a tetragonal structure with space group P4/nmm. Cobalt in these compounds is in an itinerant state, with its paramagnetic moment above 1.4 μB and the same orders ferromagnetically (FM) with saturation moment of around 0.20 μB below, say, 80 K. Though, LaCoPO shows single paramagnetic (PM) to ferromagnetic (FM) transition near 35 K, the NdCoPO and SmCoPO exhibit successive PM-FM-anti-ferromagnetic (AFM) transitions. Both FM and AFM transition temperatures vary with applied fields. Although the itinerant ferromagnetism occurs with small saturation moment, typical anti-ferromagnetic (AFM) transitions (TN1, TN2) are observed at 60 K and 14 K for Nd and 70 K and 40 K for Sm. This FM-AFM transition of Co spins in NdCoPO and SmCoPO is both field and temperature dependent. The magneto-transport of NdCoPO and SmCoPO distinctly follows their successive PM-FM-AFM transitions. It is clear that Sm/Nd (4f) interacts with the Co (3d) in first-time-synthesized Sm/NdCoPO.