Magnetic Susceptibilities of Co²⁺ in KMgF₃ and Effects of Exchange Interaction

抄録

The measurements of the magnetic susceptibilities have been made in the temperature range of 1.5°K∼300°K for three KMg_1−xCo_xF₃ single crystals with x=0.025, 0.050, and 0.110. The temperature dependence of the magnetic susceptibilities at high temperatures can be explained from the Pryce’s formula for a single Co²⁺ in an octahedral field. The deviations from the Pryce’s formula are found at low temperatures. These deviations can be explained by the effect of the exchange interactions between the neighboring Co²⁺ in the crystals. By assuming that the Co²⁺ ions are randomly distributed in the Mg²⁺ site, the contributions from the various types of isolated clusters to the total susceptibility are calculated. The observed susceptibilities can be fitted to the calculated values, if the exchange interaction is taken as −J(s_i·s_j) with J equal to −70±10cm⁻¹, where s is the fictitious spin, 1/2, of the ground state of a single Co²⁺ in an octahedral field.