Temperature dependence of magnetization reversal processes in exchange-spring magnets

We investigated the temperature dependence of magnetization reversal processes of exchange-spring magnet, hard/soft ferromagnetic heterostructures. In most previous works, the thicknesses of the soft and hard layers were used as the main control parameters to investigate the reversal mechanism of the exchange-spring magnet. In our work, the anisotropy energy of the hard layer changes as a function of temperature, while the change in the magnetic properties of the soft layer is negligible in the temperature regime in which we are interested (between 10 and 300 K ). The magnetic hysteresis loops of SmFe/Py( = Ni(80)Fe(20)) and SmCo/Py exchange-spring magnets were measured at various temperatures. Magnetic reversal behaviors of SmFe/Py and SmCo/Py were explained using the parameters extracted from the single layer measurements, SmFe or SmCo films, and the existing theory, where the reversal mechanism is controlled by the thicknesses. With a proper conversion of the temperature dependent anisotropy energy to the scaled thickness scheme, the reversal mechanisms of SmFe/Py and SmCo/Py could be explained with a simple model theory for a wide range of temperatures. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3374678]