Metamagnetism inEu3O4

The magnetic properties of the metamagnet ${\mathrm{Eu}}_3$ ${\mathrm{O}}_4$ are analyzed using molecular-field theory. For the antiferromagnetic ground state, it is assumed that linear, ferromagnetic chains of spins (${\mathrm{Eu}}^{2+}$) are polarized along the $c$ axis of the orthorhombic unit cell, with neighboring chains antiparallel. The weakly magnetic ions ${\mathrm{Eu}}^{3+}$ provide an apparently inert magnetic background. Exchange constants are deduced from the paramagnetic Curie temperature ${\theta }_p=5\mathrm{}°$K and the critical field $H_c=2.4\mathrm{}$ kOe. The constants for first- and second-neighbor ${\mathrm{Eu}}^{2+}$ interactions are $\frac{J_1}{k}\sim 0.3°$K and $\frac{J_2}{k}\sim -0.02\mathrm{}°$K, respectively. An anisotropy field of 7 kOe is derived from the transverse magnetic susceptibility at low temperatures. This value is also obtained from a magnetic dipolar sum. Theoretical estimates of the ordering temperature give $T_c\sim 5°$K, as observed.