Magnetic anisotropy ofSm2Fe17single crystals

The previously accepted notion that the spontaneous magnetization of $\mathrm{S}{\mathrm{m}}₂\mathrm{F}{\mathrm{e}}₁₇$ lies in the basal plane of the crystal is true only approximately, and then only around room temperature. At low temperatures the magnetization, whose orientation is not fixed by the symmetry, is found to deviate from the basal plane by as much as ${10}^{\ensuremath{\circ}}$. The threefold symmetry axis is a hard direction; to magnetize the crystal in this direction, a magnetic field of about 9 T is required. The hard-axis magnetization arrives at saturation discontinuously, by way of a first-order phase transition. The behavior is a general one for trigonal ferromagnets where ${K}₁<0$ and the leading trigonal anisotropy constant is nonzero, ${K}₂^{\ensuremath{'}}\ensuremath{\ne}0$. Although of universal occurrence, the first-order transition is only visible at low temperatures, where it is accompanied by a magnetization anomaly of sufficient size.