Electron-Spin-Resonance Study of Exchange-Coupled Ni2+ Pairs in K2MgF4

Abstract

Electron-Spin-Resonance study of single Ni 2+ ions and exchange-coupled Ni 2+ pairs in K 2 MgF 4 has been made. The exchange constant of the second-nearest-neighbor pair has been determined form the positions of the pair resonance lines. In this pair, different total-spin states admix sufficiently by an axial crystal field which is comparable to the exchange interaction. At 1.6°K, the spectra of the pair have been explained by a spin Hamiltonian D c ( S 1 z 2 + S 2 z 2 )+ E c ( S 1 x 2 - S 1 y 2 + S 2 x 2 - S 2 y 2 )+ J ( S 1 · S 2 )+ D d ( S 1 · S 2 -3 S 1 x S 2 x )+ g β H ·( S 1 + S 2 ), where D c =-0.425 cm -1 , E c =-0.065 cm -1 , J =0.400 cm -1 , g =2.28 and a calculated magnetic-dipole interaction D d =0.0127 cm -1 . For the single ions at 1.6°K, D s =-0.352 cm -1 and g =2.275 in D s S z 2 + g β H · S . As estimation of the exchange interaction constants of the fourth-nearest-neighbor pair has been made.