ESR studies of the Cr3+ pair in MgO

Abstract

Next nearest neighbor Cr³⁺ pairs in MgO single crystals have been studied by ESR techniques. The spectra associated with the spin states S = 1 and S = 2 were observed. The appropriate spin Hamiltonian for the system is H = β H⋅g⋅S + J S₁⋅S₂ − j (S₁⋅S₂)² + D_s{S_z² − (1/3) S (S + 1) }, where the z axis is along 〈100〉. The axially symmetric D tensors were measured to be D_s = 0.360 cm⁻¹ and D_s = 0.105 cm⁻¹ for S = 1 and S = 2 states, respectively. From the study of intensity change of the resonance line as a function of temperature, the isotropic exchange coupling constant J = 83.3 cm⁻¹ and j = 17.9 cm⁻¹ were also determined. In addition, the temperature dependence of D_s was obtained and was attributed to thermal expansion of the crystal lattice.