Electronic structure and direct observation of ferrimagnetism in multiferroic hexagonal <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>YbFeO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>

The magnetic interactions between rare-earth and Fe ions in hexagonal rare-earth ferrites $(h\text{\ensuremath{-}}R{\mathrm{FeO}}_{3})$, may amplify the weak ferromagnetic moment on Fe, making these materials more appealing as multiferroics. To elucidate the interaction strength between the rare-earth and Fe ions as well as the magnetic moment of the rare-earth ions, element-specific magnetic characterization is needed. Using x-ray magnetic circular dichroism, we have studied the ferrimagnetism in $h\text{\ensuremath{-}}{\mathrm{YbFeO}}_{3}$ by measuring the magnetization of Fe and Yb separately. The results directly show antialignment of magnetization of Yb and Fe ions in $h\text{\ensuremath{-}}{\mathrm{YbFeO}}_{3}$ at low temperature, with an exchange field on Yb of about 17 kOe. The magnetic moment of Yb is about $1.6\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ at low temperature, significantly reduced compared with the $4.5\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{B}$ moment of a free ${\mathrm{Yb}}^{3+}$. In addition, the saturation magnetization of Fe in $h\text{\ensuremath{-}}{\mathrm{YbFeO}}_{3}$ has a sizable enhancement compared with that in $h\text{\ensuremath{-}}{\mathrm{LuFeO}}_{3}$. These findings directly demonstrate that ferrimagnetic order exists in $h\text{\ensuremath{-}}{\mathrm{YbFeO}}_{3}$; they also account for the enhancement of magnetization and the reduction of coercivity in $h\text{\ensuremath{-}}{\mathrm{YbFeO}}_{3}$ compared with those in $h\text{\ensuremath{-}}{\mathrm{LuFeO}}_{3}$ at low temperature, suggesting an important role for the rare-earth ions in tuning the multiferroic properties of $h\text{\ensuremath{-}}R{\mathrm{FeO}}_{3}$.