Anisotropic Susceptibility of La_2-xSr_xCoO_4 related to the Spin States of Cobalt

TL;DR

This study investigates the magnetic anisotropy and spin states of cobalt in La_2-xSr_xCoO_4 crystals, revealing how doping influences the cobalt spin configuration and magnetic behavior.

Contribution

It provides experimental evidence and a crystal-field model analysis of cobalt spin states and anisotropy in La_2-xSr_xCoO_4, highlighting doping-dependent spin configurations.

Findings

Magnetic anisotropy is pronounced across all samples.

Low-spin Co^3+ state for x>=0.4 confirmed.

High-spin Co^2+ state observed for x<0.4.

Abstract

We present a study of the magnetic susceptibility of La_2-xSr_xCoO_4 single crystals in a doping range 0.3<=x<=0.8. Our data shows a pronounced magnetic anisotropy for all compounds. This anisotropy is in agreement with a low-spin ground state (S=0) of Co^3+ for x>=0.4 and a high-spin ground state (S=3/2) of Co^2+. We compare our data with a crystal-field model calculation assuming local moments and find a good description of the magnetic behavior for x>=0.5. This includes the pronounced kinks observed in the inverse magnetic susceptibility, which result from the anisotropy and low-energy excited states of Co^2+ and are not related to magnetic ordering or temperature-dependent spin-state transitions.