Competition between Thermoinduced Magnetization and Uncompensated Spins

Thermoinduced magnetization (TiM) is the ferromagnetic response predicted for nanoparticles of normally antiferromagnetic materials. Unambiguous experimental observation of this phenomenon is complicated by the effects of the particle size-distribution within a sample and the uncompensated magnetic moments within a nanoparticle. Monte Carlo calculations of nanoparticles with odd numbers of spins have been employed to resolve the competition between TiM and uncompensated spins. The magnitude of the ferromagnetic response, $\langle|M|^2\rangle$, is easily resolved into the two phenomena. Analysis for the response along the direction of crystalline anisotropy, $\langle M_z^2\rangle$, is complicated by the temperature-dependent relaxation of individual spins away from the anisotropy axis. These results indicate that TiM may be confirmable in nanoparticles with uncompensated spins. However, quantitative estimates of the temperature- and anisotropy-dependence of TiM are significantly affected by uncompensated moments.