MAGNETIC HARDENING BY EXCHANGE-BIAS ON MULTILAYERED FILMS GROWN BY PULSED LASER DEPOSITION

GRANELL, P.; BILOVOL, V.; PAMPILLO, L. G.; SACCONE, F. D.

Kharkov

Conferencia; III International Conference for Young Scientists LOW TEMPERATURE PHYSICS, Kharkov, Ucrania; 2012

The existence of vacancies and defects in the crystalline structure of antiferromagnetic (AFM) or ferrimagnetic (fM) oxides generates, by uncompensated spins in magnetic domains, the exchange-bias effect when they are in contact with a ferromagnetic (FM) layer. An external magnetic field applied while cooling an AFM/FM or fM/FM system freezes antidomain states which promote remanence enhacement due to uncompensated spins. It is widely known that when the anisotropy of the oxide is high enough, hysteresis loop of the system appears horizontally biased. Otherwise, when the anisotropy is low, a magnetic hardening can be observed and these systems are promisorious as permanent magnets [1, 2]. Particularly, it was proposed that cobalt ferrite (CoFe2O4), a natural hard ferrimagnet with high Curie temperature (~ 800K), is a suitable candidate for its use as pinner layer for these systems grown by pulsed laser deposition [3]. We prepared CoFe2O4(340nm)/FM(50nm)/NM(5nm)/FM(50nm) multilayered films (NM = AlOx and TiO2, FM = Fe and Ni80Fe20) by pulsed laser deposition (Nd-YAG, λ = 355 nm). The films were grown on a <100> Si substrate. The upper free FM layer was added to reinforce the magnetization and to follow the coupling between the ?hard? fM/FM bilayer and the soft FM layer. The structural properties of the samples were analized by X-ray diffraction and scanning electron microscopy. Hysteresis loops were measured at different temperatures in a SQUID. For all the studied samples, we found different behaviours attributed to exchange.bias effect at the interface fM/FM. For instance the sample CoFe2O4/Fe/TiO2/Fe, shows an increase in its coercivity as higher as 300 percent approximately, when it is compared measurements done at room temperature (RT) with that at 50K (Figure 1). Otherwise, the exchange coupling between the pinned and free layers can be tailored by selecting the separating layer.