Intriguing complex magnetism of Co in RECoAsO (RE=La, Nd and Sm)

TL;DR

This study investigates the complex magnetic behavior of cobalt in RECoAsO compounds with different rare earth elements, revealing a transition from ferromagnetic to antiferromagnetic states influenced by magnetic interactions and external fields.

Contribution

It provides new insights into how magnetic rare earth elements alter the itinerant ferromagnetism of cobalt in RECoAsO compounds, demonstrating field and temperature dependent magnetic transitions.

Findings

Cobalt exhibits itinerant ferromagnetism with small saturation moments below 80K.

Magnetic RE elements induce AFM transitions at specific temperatures.

Magneto-transport properties follow the FM-AFM transition of Co spins.

Abstract

We synthesized bulk polycrystalline samples of RECoAsO (RE=La, Nd and Sm) by solid state reaction route in an evacuated sealed quartz tube. All these compounds are crystallized in a tetragonal structure with space group P4/nmm. The Co, in these compounds is in itinerant ferromagnetic state with its paramagnetic moment above 1.5 microB and the same orders ferromagnetically (FM) with small saturation moment of around 0.20 microB below say 80K. This bulk intrinsic magnetism of Co changes dramatically when nonmagnetic La is changed by magnetic Sm and Nd. Although the itinerant ferromagnetism occurs below 80-100K with small saturation moment, typical anti-ferromagnetic (AFM) transitions (TN1, TN2) are observed at 57K and 45K for Sm and at 69K and 14K for Nd. The transition of Co spins from FM to AFM, for magnetic Sm and Nd in RECoAsO is both field and temperature dependent. For applied fields below 100Oe, both TN1 and TN2 are seen, with intermediate fields below 1-2kOe only TN1 and above say 5kOe the AFM transition is not observed. This is evidenced in isothermal magnetization (MH) plots as well. It is clear that Sm/Nd magnetic moments interact with the ordered Co spins in adjacent layer and thus transforms the FM ordering to AFM. All the studied compounds are metallic in nature, and their magneto-transport R(T)H follows the temperature and field dependent FM-AFM transition of ordered Co spins.