  The magnetic interaction between rare-earth and Fe ions in hexagonal
rare-earth ferrites (h-REFeO3), 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-YbFeO3 by measuring the magnetization of Fe and Yb
separately. The results directly show anti-alignment of magnetization of Yb and
Fe ions in h-YbFeO3 at low temperature, with an exchange field on Yb of about
17 kOe. The magnetic moment of Yb is about 1.6 \muB at low-temperature,
significantly reduced compared with the 4.5 \muB moment of a free Yb3+. In
addition, the saturation magnetization of Fe in h-YbFeO3 has a sizable
enhancement compared with that in h-LuFeO3. These findings directly demonstrate
that ferrimagnetic order exists in h-YbFeO3; they also account for the
enhancement of magnetization and the reduction of coercivity in h-YbFeO3
compared with those in h-LuFeO3 at low temperature, suggesting an important
role for the rare-earth ions in tuning the multiferroic properties of h-REFeO3.
