Impurity Spin Resonance in Antiferromagnetic FeCl₂

Abstract

Electron spin resonance of Fe³⁺ and Mn²⁺ ions in antiferromagnetic FeCl₂ was investigated at low temperatures using various microwave frequencies and pulsed magnetic fields. Experimental results show that these impurities in FeCl₂ occupy mainly the substitutional position and couple with host Fe²⁺ spins by rather weak exchange interaction. Using the metamagnetic properties of FeCl₂, these resonances were investigated both above and below the critical field H_c. The intralayer and interlayer exchange field H₁ and H₂ of these impurities were found by analysis to be
H₁(AF)=8.0 kOe H₂(AF)=4.2 kOe for Fe³⁺ spins,
H₁(F)=21.6 kOe H₂(AF)=13.8 kOe for Mn²⁺ spins,
where AF and F mean the antiferromgnetic and ferromagnetic exchange interactions with Fe²⁺ spins, respectively. Interstitial impurity spin resonance was also found and the exchange interaction with neighboring Fe²⁺ spins is estimated.