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Specular reflection effects on anisotropic magnetoresistance of magnetic thin films were studied.

An analytical calculation of the shape of the magnetoresistive response of spin-valve structures with synthetic antiferromagnetic pinned layers is presented. It was found that specular reflection at the CoFe/Ru interface must be introduced to account for the experimental dat.

Microstructural effects on the antiferromagnetic layer were investigated on IrMn/Co exchange biased square dots. IrMn grain size and distributions were tuned by changing Cu buffer layer or IrMn thicknesses. Lateral dimensions from 200 to 50nm were varied. Exchange bias (Hex) variability was analysed through focused Kerr measurements on small groups of dots. Patterned samples presented average exchange bias values following the trends and values of full sheet samples. Concerning the dot to dot behaviour, it resulted that IrMn microstructure variations have minor effects on Hex variability, because no particular trend is observed as a function of grain size and distribution. The variability is attributed to geometry variation and Co intrinsic variability.

Magnetic devices are often subject to thermal processing steps, such as field cooling to set exchange bias and annealing to crystallize amorphous magnetic electrodes. These processing steps may result in interdiffusion and the subsequent deterioration of magnetic properties. In this study, we investigated thermally-activated diffusion in Cu/Co/IrMn/Pt exchange biased polycrystalline thin-film structures using atom probe tomography. Images taken after annealing at 400°C for 60 min revealed Mn diffusion into Co grains at the Co/IrMn interface and along Pt grain boundaries for the IrMn/Pt stack, i.e., a Harrison type C regime. Annealing at 500°C showed further Mn diffusion into Co grains. At the IrMn/Pt interface, annealing at 500°C led to a type B behavior since Mn diffusion was detected both along Pt grain boundaries and also into Pt grains. The deterioration of the films' exchange bias properties upon annealing was correlated to the observed diffusion. In particular, the topmost Pt capping layer thickness turned out to be crucial since a faster deterioration of the exchange bias properties for thicker caps was observed. This is consistent with the idea that Pt acts as a getter for Mn, drawing Mn out of the IrMn layer. [ABSTRACT FROM AUTHOR]

Magnetic measurements have been performed on thin films with structures Ta/Pt/Co/[AlO.sub.x] to investigate the dependence of the perpendicular magnetic anisotropy induced at the Co/[AlO.sub.x] interface on both Co thickness and annealing temperature. The choice of the capping layers to protect the oxide layer is shown to be important. The interfacial anisotropy increases strongly with increasing annealing temperature, from 0.7 to 1.4 erg/[cm.sup.2], without a major change of the volume anisotropy (11 [10.sup.6] erg/[cm.sup.3]). As a consequence, the critical Co thickness (at which the magnetic moment switches from perpendicular to inplane orientation), increases a lot with annealing and reaches values larger than 3 nm after annealing at 375[degrees]C. Index Terms--Annealing effects, Co/AlO interface, extraordinary hall effect (EHE), perpendicular magnetic anisotropy.

Exchange bias without antiferromagnetic layer was observed in systems consisting of two exchange coupled ferromagnetic materials: [(Pt/Co).sub.n] multilayer (with out-of-plane anisotropy) and permalloy, NiFe, (with in-plane anisotropy). We investigated the influence of various parameters on this phenomenon: Pt buffer layer thickness, number of repeats in the multilayer, thickness of the NiFe layer. Annealing yields a doubling in the magnitude of the loop shift as a result of an improved texture and mosaicity of the films. Index Terms--Coercive field, exchange bias, perpendicular anisotropy.

A thermally assisted writing procedure is proposed in a tunnel junction based magnetic random access memory cell. The magnetic layers of the tunnel junction are both exchange-biased with antiferromagnetic layers, the reference layer having a much higher blocking temperature than the storage layer. In the operating mode, a current pulse sent through the junction generates enough heat to raise the temperature of the storage layer above its blocking temperature, without affecting the pinning of the reference layer. The concept is demonstrated here for an isolated junction using an homogeneous external magnetic field. Index Terms--Autiferromagnetic materials, metal insulator metal (MIM) devices.

The exchange anisotropy of pseudo-single crystalline Mn-Ir/Co-Fe bilayers with crystallographic orientations is discussed. Extra large value of 0.73 erg/cm(super 2) was observed in the unidirectional anisotropy constant J(sub K) of the (110)-epitexial bilayer with d(sub AF)=4 nm.

The exchange bias effects in circular nanodots of ~130nm in diameter are examined. The exchange bias field is enhanced by 30 percent along the field-cooling direction in the dots.

The thermal stability of pinned synthetic ferrimagnets with perpendicular magnetic anisotropy is explored. The order of Pt/Co multilayers switching changes during magnetization reversal depending on the temperature due to the different thermal evolution of A(sub Ru) and A(sub pinning).

Spin torque driven excitations in spin valves and tunnel junctions are often investigated for a two magnetic layer system for which a polarizer (fixed magnetization) and a free layer can be distinguished. In the search for improved microwave properties and to understand the role of different coupling mechanisms between the magnetic layers, here, the excitation spectrum of an exchange coupled two layer synthetic ferrimagnet (SyF) system is investigated numerically with spin momentum transfer acting on both layers simultaneously. This self-polarised two layer system does not contain an external polarizer, and excitation of coupled modes arises due to the mutual spin transfer torque and the Ruderman-Kittel-Kasuya-Yosida interlayer exchange coupling. The current-field state diagrams of static and dynamic states are reported as a function of the interlayer exchange coupling strength. The numerically determined critical boundaries are well reproduced by an analytical stability analysis. The dynamic steady states reveal an optic-like mode at low magnetic fields, which becomes progressively acoustic-like for increased magnetic fields and currents. The frequency of these modes can be tuned by the film thickness and the strength of the interlayer exchange interaction. The results presented here will provide an important guide for designing spin torque oscillators that exploit the dynamic coupling between layers and, furthermore, they will provide a basis to test analytical models of spin torque driven coupled excitations. [ABSTRACT FROM AUTHOR]

The magnetic and transport properties of exchange-biased perpendicular spin valves (PSVs), which associate a free (Co/Pt) multilayer with a pinned (Co/Pt)/FeMn multilayer [FeMn as the antiferromagnetic (AF) layer] with different nonmagnetic spacers (Pt, Cu, Al2O3), are investigated. The metallic PSVs with Cu spacers exhibited giant magnetoresistance but the amplitude was only of the order of 1% due to major current shunting.

Research into the magnetization reversal in polycrystalline exchange-coupled NiO/Co bilayers over 10 decades of field sweep rate dH/dt for varying NiO and Co thicknesses is presented. It was found that domain wall propagation and domain nucleation control the magnetization reversal and low and high sweep rates respectively.

Research into the impact of the scattering at the edges of submicronic magnetic multilayer pillars on the current-perpendicular-to-plane resistance and magnetoresistance of these structures is presented. As the lateral size of the pillars falls below 100 nm, it is demonstrated that this scattering prompts a strong rise in the current-perpendicular-to-plane resistivity.

A study was conducted to analyze thermal relaxation in NiO pseudospin valves. Two different methods were utilized to carry out the analysis. The magnetoresistance response was measured at frequencies of the applied field ranging from 0.4 to 120 Hz in the temperate range 20 to 125 degrees C. Moreover, the time-decay resistance was measured at a fixed applied field which was near the quasistatic switching field.

A code has been developed based on the semi-classical theory of giant magnetoresistance of Camley and Barnas [1]. It computes the sheet conductance and magnetoresistance of spin.valve structures. The input parameters are phenomenological transport parameters (mean-free paths and reflection/transmission coefficients at interfaces). These parameters are fairly well known in most conventional materials. Several refinements have been introduced into the initial theory, in particular spin-intermixing due to magnon scattering, anisotropy in mean-free paths, and angular dependence of transmission through the interfaces. A few examples of the use of this code are described in this paper. Such code could be used as a guideline in the optimization of spin-valves. Index terms- spin-valves, semi-classical theory of giant magnetoresistance.