Induced four fold anisotropy and bias in compensated NiFe/FeMn double layers

A vector spin model is used to show how frustrations within a multisublattice antiferromagnet such as FeMn can lead to four-fold magnetic anisotropies acting on an exchange coupled ferromagnetic film. Possibilities for the existence of exchange bias are examined and shown to exist for the case of weak chemical disorder at the interface in an otherwise perfect structure. A sensitive dependence on interlayer exchange is found for anisotropies acting on the ferromagnet through the exchange coupling, and we show that a wide range of anisotropies can appear even for a perfect crystalline structure with an ideally flat interface.Comment: 7 pages, 7 figure

An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device

We present the first spintronic semiconductor field effect transistor. The injector and collector contacts of this device were made from magnetic permalloy thin films with different coercive fields so that they could be magnetized either parallel or antiparallel to each other in different applied magnetic fields. The conducting medium was a two dimensional electron gas (2DEG) formed in an AlSb/InAs quantum well. Data from this device suggest that its resistance is controlled by two different types of spin-valve effect: the first occurring at the ferromagnet-2DEG interfaces; and the second occuring in direct propagation between contacts.Comment: 4 pages, 2 figure

Martensitic transition and magnetoresistance in a Cu-Al-Mn shape memory alloy. Influence of aging

We have studied the effect of ageing within the miscibility gap on the electric, magnetic and thermodynamic properties of a non-stoichiometric Heusler Cu-Al-Mn shape-memory alloy, which undergoes a martensitic transition from a $bcc$-based ($\beta$-phase) towards a close-packed structure ($M$-phase). Negative magnetoresistance which shows an almost linear dependence on the square of magnetization with different slopes in the $M$- and $\beta$-phases, was observed. This magnetoresistive effect has been associated with the existence of Mn-rich clusters with the Cu$_2$AlMn-structure. The effect of an applied magnetic field on the martensitic transition has also been studied. The entropy change between the $\beta$- and $M$-phases shows negligible dependence on the magnetic field but it decreases significantly with annealing time within the miscibility gap. Such a decrease is due to the increasing amount of Cu$_2$MnAl-rich domains that do not transform martensitically.Comment: 9 pages, 9 figures, accepted for publication in PR

Dipolar interactions and anisotropic magnetoresistance in metallic granular systems

We revisit the theory of magnetoresistance for a system of nanoscopic magnetic granules in metallic matrix. Using a simple model for the spin dependent perturbation potential of the granules, we solve Boltzmann equation for the spin dependent components of the non equilibrium electronic distribution function. For typical values of the geometric parameters in granular systems, we find a peculiar structure of the distribution function of conduction electrons, which is at variance with the two-current model of conduction in inhomogeneous systems. Our treatment explicitly includes the effects of dipolar correlations yielding a magnetoresistance ratio which contains, in addition to the term proportional to the square of uniform magnetization (), a weak anisotropic contribution depending on the angle between electric and magnetic fields, and arising from the anisotropic character of dipolar interactions.Comment: 9 pages, 2 figures, accepted in PR

LINEAR AND NONLINEAR SPIN WAVE EXCITATIONS IN SUPERLATTICES AND AT SURFACES

Nous discutons les ondes de spins dans un super-réseau composé alternativement de couches magnétiques et nonmagnétiques. Une couche magnétique isolée a des ondes de spins de surface à ses limites. Dans une structure composée de couches, ces ondes interagissent et forment une bande d'excitations volumique du super-réseau. Sous certaines conditions il existe aussi des modes de surface du super-réseau semi-infini. Ces excitations peuvent être étudiées par diffusion de la lumière et nous présentons les résultats de la théorie et les comparons avec ceux de l'expérience. Nous discutons aussi comment la nonlinéarité de l'équation de Bloch pour les spins conduit au couplage des ondes des spins. Nous notons que l'interaction de deux ondes de surface peut produire une troisième onde de surface ainsi que l'interaction de deux ondes de volume peut produire une onde de surface.We discuss the spin waves of a superlattice composed of alternate layers of magnetic and nonmagnetic materials. Each magnetic film in isolation has surface spin waves on its boundaries. In the layered structure, these interact to form a band of bulk excitations of the superlattice. Under certain conditions a surface mode of the semi-infinite superlattice also exists. These excitations can be probed by light scattering experiments, and we give theoretical results and compare them with experiment. We also discuss how the nonlinearity of the Bloch spin equation leads to a mixing of spin waves. We note the possibility of two surface waves interacting to produce a third surface wave or even of two bulk waves interacting to produce a surface spin wave

Magnetic multilayers

We discuss some of the fundamental properties unique to magnetic multilayers. Due to a simple competition between exchange and Zeeman energies, complex, spatially nonuniform spin configurations are found to exist. Both bulk and surface phase transitions are discussed. We also consider spin waves in magnetic multilayers with particular attention to canted spin configurations. Spin wave excitations provide a powerful method for studying exchange interactions and spin configurations. Here effective medium calculations are compared to microscopic calculations which need no approximations. Finally, the phenomenon of giant magnetoresistance in magnetic multilayers, where the resistivity of the metallic structure can be changed by over 60% at room temperature, is discussed. A Boltzmann equation approach which involves both bulk and interface spin-dependent scattering is used to understand and predict the transport properties of the multilayer systems, and comparisons between theory and experiment are stressed

Magnetic multilayers: spin configurations, excitations and giant magnetoresistance

The authors discuss some of the fundamental properties unique to magnetic multilayers. Complex spin configurations are examined for many different systems and are shown to arise from a simple competition between exchange and Zeeman energies. The spin configurations found in multilayer systems determine macroscopic properties such as the static susceptibility and magnetization, and can lead to anomalous field and temperature behaviour. The authors also discuss the dynamic behavior of magnetic multilayers. Emphasis is placed on spin waves in magnetic multilayers with canted spin configurations and the softening of modes at magnetic phase transitions. Furthermore they show that spin wave excitations provide a powerful method for studying exchange interactions and spin configurations. Finally, the phenomenon of giant magnetoresistance in magnetic multilayers where the resistivity of the metallic structure can be changed by over 60% at room temperature, is discussed. Simple theoretical approaches are used to understand and predict the properties of the multilayer systems and comparisons between theory and experiment are stressed