Magnetic coupling in multilayered exchange-spring films

F. D. SACCONE; VAVASSORI, P.; BERGER, A.

CABA

Workshop; Latin American Workshop on Magnetism and Magnetic Materials; 2013

It is widely known that the exchange-bias phenomenon induces shifts and coercive field increases in the hysteresis loops of nanostructured magnetic materials composed of both, antiferromagnetic (AFM) and ferromagnetic (FM) phases. The general observation of exchange bias in AFM/FM hybrid structures can also be applied to diluted ferrimagnets (fM), such as cobalt ferrite, for which defects or vacancies in the bulk are responsibles for the interlayer exchange coupling at the interface between the fM and adjacent ferromagnetic (FM) layers. In this way, it is possible to induce a magnetic hardening of FM layers after field cooling in Fm/fM hybrid structures. In order to investigate this possibility, two families of multilayered thin films of TiO2/FM/TiO2/FM/CoFe2O4 (FM= Fe and Py) were grown by means of the pulsed layer deposition technique with a total thicknesses of less than 300 nm. Structural properties were analyzed by X-Ray Diffraction and the Fe K-edge absorption was followed by X-Ray fluorescence at grazing incidence. The bulk magnetic properties of the fabricated samples exhibit certain similarities: at 10 K, the coercive field of their hysteresis loops is enhanced to approximately 1T and a clear decoupling between the pinned (the layer in contact with CoFe2O4) and the second FM layer (free layer) was observed for both samples. In contrast to this, both films appear to be coupled when their hysteresis loops were measured at room temperature, Furthermore, by using the FORC diagram technique we detected that the free and pinned layers are less coupled for the Py samples. This result was confirmed by magneto-optical Kerr effect (MOKE) magnetometry measurements.