  Phenomenological analysis for the temperature dependence of the
magnetocrystalline anisotropy (MA) in rare earth magnets is presented. We
define phenomenological power laws applicable to compound magnets using the
Zener theory, apply these laws to the magnetocrystalline anisotropy constants
(MACs) of Nd$_2$Fe$_{14}$B magnets. The results indicate that the MACs obey the
power law well, and a general understanding for the temperature-dependent MA in
rare earth magnets is obtained through the analysis. Furthermore, to examine
the validity of the power law, we discuss the temperature dependence of the
MACs in Dy$_2$Fe$_{14}$B and Y$_2$Fe$_{14}$B magnets as examples wherein it is
difficult to interpret the MA using the power law.
