Temperature and frequency dependence of exchange anisotropy effects in oxidized NiFe films

Abstract

Hysteresis loops have been measured for thin NiFe films between 5 and 300 K using the magneto-optic Kerr effect. Films that are free of any surface oxide do not show a displacement of the easy-axis loop along the field axis, and the coercive force and anisotropy field are very weak functions of the temperature. Oxidized films show striking exchange anisotropy effects; displaced loops appear below a transition temperature ranging from 30 to 90 K as the film is more heavily oxidized. Loop width and anisotropy field increase with decreasing temperature, exhibiting a change in slope in the neighborhood of the transition temperature. The steady-state parameters have characteristic frequency dependences; with increasing frequency the loop displacement and anisotropy field increase and the loop width decreases in the range 0.05–100 Hz. The interpretation of these results in terms of thermal aftereffect taking place in the antiferromagnetic oxide is presented in a companion paper.

Magnetization reversal of an individual exchange-biased permalloy nanotube

“…Indeed, similar blocking temperatures around T ≈ 30 K have been previously found for naturally oxidized Py thin films [28]. The decreasing extent of the continuous reversal region with increasing temperature could be the result of the inhomogeneity and graininess of the oxide shell.…”

Contribution of low-temperature degrees of freedom to the anisotropy in Co/CoO exchange coupled bilayers

“…The AFM sublattice orientation m then moves in the free-energy landscape determined by the crystalline anisotropy energy of the AFM and the exchange coupling to the FM. This situation has been analyzed by many authors [5,6] and provides a convincing qualitative description of the dissipation close to T Ã N or T B . However, mechanisms involving the AFM do not adequately explain the low-temperature degrees of freedom since none are independent of the CoO thickness.…”

Size Dependence of Structures and Properties of Magnetic Materials

“…[293]) and H e and T B are sizedependent, which is emphasized in this section. Besides, H e and T B are also functions of AFM orientation (compensated versus uncompensated AFM surface [298][299][300][301][302][303] and in-plane versus out-of-plane AFM spins [298,299,302]), of FM/AFM interface disorder (roughness [299,301,302,[304][305][306], crystallinity [307,308], grain size [309,310], of interface impurity layers [311]), and of strain effect [312][313][314], of stoichiometry [293] or of presence of multiple phases [315] and so forth.…”