Exchange Interactions and Magnetic Susceptibilities of Ni2+ in KMgF3 and K2MgF4

Magnetic susceptibilities of KMg (1- x ) Ni x F 3 and K 2 Mg (1- x ) Ni x F 4 (0≦ x ≦0.121) have been measured in the temperature range from 1.6°K to 300°K, and the exchange interactions between neighboring Ni 2+ ions have been evaluated. The analysis of the data has been made on the assumption that Ni 2+ ions distribute randomly in Mg 2+ sites and form various types of clusters coupled by the exchange interactions. In KMgF 3 , the nearest-neighbor exchange J 1 is 110±10°K and the next-nearest-neighbor exchange J 2 is 0.5±0.1°K, where an exchange interaction between neighboring spins s i and s j is written as J ( s i · s j ). In K 2 MgF 4 , J 1 is 120±10°K. The intraplane next-nearest-neighbor exchange J 2 and the interplane-nearest-neighbor exchange J 3 can not be determined uniquely, but the most probable values are \(J₂{}0.5\)°K and \(J₃{}0\). The Van Vleck paramagnetic susceptibilities of Ni 2+ in both salts have been found to be 2.83×10 -4 cgsemu/mol within the experimental errors of 10%.