Van Vleck paramagnetism of the trivalent Eu ions

Magnetic susceptibilities of Eu₂O₃, EuF₃ and EuBO₃ have been measured over the wide temperature range 5-650 K. The Van Vleck paramagnetism, with the ground state of ⁷F₀ (S=3, L=3), has been investigated comprehensively. The temperature independent paramagnetism emerges manifestly below approximately 100 K. The variation of the susceptibility with temperature for EuBO₃ is in satisfactory agreement with the coupling constant , where the spin-orbit interaction is λL·S for the Russell-Saunders coupling on the basis of Van Vleck theory with one parameter λ. The value of can fit the susceptibility data of EuF₃. The deviation from the theory arises in Eu₂O₃. This discrepancy originates mainly from the influence of the crystalline field. Susceptibility of Gd₂O₃, having the ground state of ⁸S_7/2 (S=7/2, L=0), is also presented as a magnetic standard compound in comparison with these results.