Possible helimagnetic order in Co4+-containing perovskites Sr1-xCaxCoO3

TL;DR

This study explores how lattice changes in Sr1-xCaxCoO3 perovskites influence magnetic states, revealing potential helimagnetic order at high calcium content due to structural distortion and electronic interactions.

Contribution

It provides evidence for possible helimagnetic order in Co4+-containing perovskites induced by lattice distortion and electronic effects, supported by synthesis, experiments, and first-principles calculations.

Findings

Structural transition from cubic to orthorhombic at x>0.6

Persistence of ferromagnetism with slight T_C drop in orthorhombic phase

Emergence of antiferromagnetic or helimagnetic behavior at x>0.8

Abstract

We systematically synthesized perovskite-type oxides Sr1-xCaxCoO3 containing unusually high valence Co4+ ions by a high pressure technique, and investigated the effect of systematic lattice change on the magnetic and electronic properties. As the Ca content x exceeds about 0.6, the structure changes from cubic to orthorhombic, which is supported by the first-principles calculations of enthalpy. Upon the orthorhombic distortion, the ground state remains to be apparently ferromagnetic with a slight drop of the Curie temperature. Importantly, the compounds with x larger than 0.8 show antiferromagnetic behavior with positive Weiss temperatures and nonlinear magnetization curves at lowest temperature, implying that the ground state is noncollinear antiferromagnetic or helimagnetic. Considering the incoherent metallic behavior and the suppression of the electronic specific heat at high x region, the possible emergence of a helimagnetic state in Sr1-xCaxCoO3 is discussed in terms of the band-width narrowing and the double-exchange mechanism with the negative charge transfer energy as well as the spin frustration owing to the next-nearest neighbor interaction.