  The random-anisotropy Heisenberg model is numerically studied on lattices
containing over ten million spins. The study is focused on hysteresis and
metastability due to topological defects, and is relevant to magnetic
properties of amorphous and sintered magnets. We are interested in the limit
when ferromagnetic correlations extend beyond the size of the grain inside
which the magnetic anisotropy axes are correlated. In that limit the coercive
field computed numerically roughly scales as the fourth power of the random
anisotropy strength and as the sixth power of the grain size. Theoretical
arguments are presented that provide an explanation of numerical results. Our
findings should be helpful for designing amorphous and nanosintered materials
with desired magnetic properties.
