An Investigation of V²⁺ Impurity Center in KMgF₃ and KZnF₃ by ⁵¹V-ENDOR Measurements

51 V-ENDOR measurements for a substitutional V 2+ impurity center in KMgF 3 and KZnF 3 have been made using a microwave frequency of 35 GHz. The spin-Hamiltonian parameters including higher order hyperfine interaction term U ( S 3 I ) have been determined as following values: A =-258.337±0.005 MHz, g I β N / h =(11.255±0.005)×10 -4 MHz/G, U =0.110±0.005 MHz for KMgF 3 , and A =-259.157±0.005 MHz, g I β N / h =(11.260±0.005)×10 -4 MHz/G, U =0.118±0.005 MHz for KZnF 3 . To interprete the parameter U , calculation for V 2+ in a cubic octahedral crystalline field including the contribution from excited 2 G term is carried out. Other parameters are also discussed. A new value for the nuclear magnetic moment of 51 V nucleus is proposed.