2, University of Nebraska–Lincoln, Lincoln, Nebraska, United States
A first hand magnetocaloric effect (MCE) in rare-earth free Fe-W (Ta) thin film systems, induced by simultaneous transformation in structural and ordered magnetic phases, is reported. The MCE has been realized by varying the levels and types of dopants in the Fe-host. These materials systems in thin film form have shown a crystallographic phase transition from a regular body center cubic (BCC) crystal structure to a distorted BCC. Applying the Maxwell relation to the magnetization (M) versus magnetic field (H) curves at various temperatures, we have calculated dM/dT vs H the integration of which provides a quantitative information about isothermal entropy change. We have observed positive a MCE with a maximum entropy value of 6.9 J/K-m3 for the magnetic field changing from 0.05 – 0.5 T. The mass specific entropy changes are small in comparison with existing magnetocaloric material. A peak in dM/dT versus H has shown that maximum entropy change takes place around 0.15 T, which is more than an order of magnitude lower than the magnetic fields generally used to realize a large MCE effect.