Possible helimagnetic order in Co4+-containing perovskites Sr1−xCaxCoO3
Hidefumi Takahashi,
Masaho Onose,
Yasuhito Kobayashi,
Takahiro Osaka,
Soushi Maeda,
Atsushi Miyake,
Masashi Tokunaga,
Hajime Sagayama,
Yuichi Yamasaki,
Shintaro Ishiwata
Affiliations
Hidefumi Takahashi
Division of Materials Physics and Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560–8531, Japan
Masaho Onose
Department of Applied Physics, the University of Tokyo, Tokyo 113–8656, Japan
Yasuhito Kobayashi
Division of Materials Physics and Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560–8531, Japan
Takahiro Osaka
Department of Applied Physics, the University of Tokyo, Tokyo 113–8656, Japan
Soushi Maeda
Division of Materials Physics and Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560–8531, Japan
Atsushi Miyake
The Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba 277-8581, Japan
Masashi Tokunaga
The Institute for Solid State Physics, the University of Tokyo, Kashiwa, Chiba 277-8581, Japan
Hajime Sagayama
Institute of Materials Structure Science (IMSS), High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
Yuichi Yamasaki
National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305-0047, Japan
Shintaro Ishiwata
Division of Materials Physics and Center for Spintronics Research Network (CSRN), Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560–8531, Japan
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 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 Sr1−xCaxCoO3 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.
