Anisotropic Magnetization of Ytterbium Orthoferrite

The magnetization of single-crystal ytterbium orthoferrite (YbFeO3) was measured from 4.2° to 300°K in fields1 up to 110 kOe. At high temperatures a small spontaneous moment appears along the c direction. The magnetization is proportional to field along the a, b, and c directions. As the temperature is lowered, the field-dependent magnetization parallel to a increases rapidly and approaches a saturation value of 3.2 μb at 4.5°K. Along the c direction, an anomalously small increase in spontaneous magnetization with decreasing temperature is observed below 100°K. In addition, below 2.3°K the magnetization becomes temperature independent but still retains a large field dependence. From this we predict that either: (1) the magnetic unit cell is larger than the crystallographic cell, yielding Yb magnetic sublattices canted from the c direction; or (2) the Yb3+ ground state is not a Kramers doublet widely separated from the remaining levels. The high-field magnetization along the b directions is markedly smaller than that along a. It appears that the driving force for the magnetization reorientation is a huge rare-earth anisotropy, which tends to align the Yb spins along the a axis, along with the net iron magnetization. It is possible to explain our recent low-temperature magnetostriction measurements on YbFeO3, where a sizeable change in length is found for H ∥ a and H ∥ c, whereas a small magnetostriction is observed for H ∥ b.