Ressonância ferromagnética em filmes simples ferromagneticos (FM) e bicamadas ferro/antiferromagnéticas (FM/AF) em função da temperatura

Abstract

Spintronic is a great promise for advance in the electronic industry. Diferently to actual electronic semiconductor devices which use only current of electrical charges spintronic is based on currents of polarized spins. Devices as for example spin valves consist of two or more conducting ferromagnetic (FM) thin films which change drastically theirelectrical resistance (giant magnetoresistance) depending on the relative alignment of their magnetization directions. Devices based on different magnetic thin films are not only interesting or storing information but also for biological and gas sensors. Due to the great importance it is fundamental to understand well the magnetic properties of ferromagnetic(FM) films and ferromagnetic/antiferromagnetic (FM/AF) bilayer that compose spin valves.n this work we present results of preparation and characterization of thin FM filmes and FM/AF bilayers. Thin ferromagnetic fillms of Cobalt (Co) and Permalloy (Py) and bilayers FM/AF consisting of Py/IrMn on Si (100) substrates were produced by obliquesputtering technique resulting in polycrystalline thin films with elongated grains oriented perpendicular to the deposition direction. We use the ferromagnetic resonance (FMR) as the principal magnetic characterization technique that through angular dependencies inthe film plane allows to extract important magnetic parameters as for example the effective magnetization, magnetic anisotropy and magnetic relaxation processes in addition to the exchange bias in case of FM/AF bilayers. The main objective and focus of our work is to obtain experimental data of those magnetic properties as a function of temperature (10 - 300 K), data almost inexistent in the literature, and model these properties with the phenomenological ferromagnetic resonance theory. The effective magnetization and magnetic anisotropies obtained from the FMR angular dependencies of the resonant field as a function of temperature were numerically fitted according to Bloch's law and Callen's equation, respectively, and showed good agreement with theory. Data about the magnetic relaxation processes in FM and FM/AF bilayer were obtained from the FMR angular dependencies of the line widths of the resonant line which showed intrinsic and extrinsic contributions due to Gilbert and two magnons relaxation, respectively. Only the intrinsic Gilbert relaxation is affected by temperature. We show also that heat treatments at about 300oC of sputtered FM films increase the effective magnetization and the magnetic anisotropy. Experimentally, it was verified that the bilayers FM/AF present a critical temperature TR (i) below TR the rotational anisotropy increases exponentially and the exchange bias decreases and ii) above TC both anisotropy decreases.