  Metamagnetic transitions in single-crystal rare-earth nickel borocarbide
HoNi$_2$B$_2$C have been studied at T\approx 1.9 K with a Quantum Design torque
magnetometer. This compound is highly anisotropic with a variety of
metamagnetic states at low temperature which includes antiferromagnetic,
ferrimagnetic, non-collinear and ferromagnetic-like (saturated paramagnet)
states. The critical fields of the transitions depend crucially on the angle
$\theta$ between applied field and the easy axis [110]. Measurements of torque
along the c-axis have been made while changing the angular direction of the
magnetic field (parallel to basal tetragonal $ab$-planes) and with changing
field at fixed angle over a wide angular range. Two new phase boundaries in the
region of the non-collinear phase have been observed, and the direction of the
magnetization in this phase has been precisely determined. At low field the
antiferromagnetic phase is observed to be multidomain. In the angular range
very close to the hard axis [100] ($-6^{\circ} \lesssim\phi \lesssim
6^{\circ}$, where $\phi$ is the angle between field and the hard axis) the
magnetic behavior is found to be ``frustrated'' with a mixture of phases with
different directions of the magnetization.

Strongly Correlated Electrons;Superconductivity