• Onose, Masaho
• Kobayashi, Yasuhito
• Osaka, Takahiro
• Maeda, Soushi
• Tokunaga, Masashi

Abstract

<jats:p> We systematically synthesized perovskite-type oxides Sr<jats:sub>1−x</jats:sub>Ca<jats:sub>x</jats:sub>CoO<jats:sub>3</jats:sub> containing unusually high valence Co<jats:sup>4+</jats:sup> 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 the lowest temperature, implying that the ground state is non-collinear antiferromagnetic or helimagnetic. Considering the incoherent metallic behavior and the suppression of the electronic specific heat at the high x region, the possible emergence of a helimagnetic state in Sr<jats:sub>1−x</jats:sub>Ca<jats:sub>x</jats:sub>CoO<jats:sub>3</jats:sub> is discussed in terms of the bandwidth 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. </jats:p>

Topics

• perovskite
• impedance spectroscopy
• compound
• magnetization
• Curie temperature
• specific heat