  The origins of the anomalous temperature dependence of magnetocrystalline
anisotropy in (Fe$_{1-x}$Co$_{x}$)$_{2}$B alloys are elucidated using
first-principles calculations within the disordered local moment model.
Excellent agreement with experimental data is obtained. The anomalies are
associated with the changes in band occupations due to Stoner-like band shifts
and with the selective suppression of spin-orbit "hot spots" by thermal spin
fluctuations. Under certain conditions, the anisotropy can increase, rather
than decrease, with decreasing magnetization due to these peculiar electronic
mechanisms, which contrast starkly with those assumed in existing models.
