Enhancement of Exchange Bias and Perpendicular Magnetic Anisotropy in CoO/Co Multilayer Thin Films by Tuning the Alumina Template Nanohole Size.

The interest in magnetic nanostructures exhibiting perpendicular magnetic anisotropy and exchange bias (EB) effect has increased in recent years owing to their applications in a new generation of spintronic devices that combine several functionalities. We present a nanofabrication process used to induce a significant out-of-plane component of the magnetic easy axis and EB. In this study, 30 nm thick CoO/Co multilayers were deposited on nanostructured alumina templates with a broad range of pore diameters, 34 nm ≤ Dp ≤ 96 nm, maintaining the hexagonal lattice parameter at 107 nm. Increase of the exchange bias field (HEB) and the coercivity (HC) (12 times and 27 times, respectively) was observed in the nanostructured films compared to the non-patterned film. The marked dependence of HEB and HC with antidot hole diameters pinpoints an in-plane to out-of-plane changeover of the magnetic anisotropy at a nanohole diameter of ∼75 nm. Micromagnetic simulation shows the existence of antiferromagnetic layers that generate an exceptional magnetic configuration around the holes, named as antivortex-state. This configuration induces extra high-energy superdomain walls for edge-to-edge distance >27 nm and high-energy stripe magnetic domains below 27 nm, which could play an important role in the change of the magnetic easy axis towards the perpendicular direction.

Applied Trends in Magnetic Rare Earth/Transition Metal Alloys and Multilayers.

Ferrimagnetic thin films formerly played a very important role in the development of information storage technology. Now they are again at the forefront of the rising field of spintronics. From new, more efficient magnetic recording media and sensors based on spin valves to the promising technologies envisaged by all-optical switching, ferrimagnets offer singular properties that deserve to be studies both from the point of view of fundamental physics and for applications. In this review, we will focus on ferrimagnetic thin films based on the combination of rare earths (RE) and transition metals (TM).

Substrate-Induced Strain Effect on Structural and Magnetic Properties of La0.5Sr0.5CoO3 Films.

We present a detailed study about the substrate-induced strain and thickness effects on the structure and magnetic properties of La0.5Sr0.5CoO3 films. The in-plane tensile or compressive strain imposed by four different substrates configures an in-plane or out-of-plane easy axis, respectively. The presence of a soft magnetic phase at the interface is also conditioned by the type of strain. The obtained results are discussed in terms of the different anisotropies that participate and control the final magnetic behavior. The relevance of these results lies in the feasibility of La0.5Sr0.5CoO3 in memory applications and spintronic devices.

Strong magnetization and anisotropy of Mn5Ge3thin films on Ge(001).

We report on the growth of Mn5Ge3thin films on Ge(001) substrates following two methods: solid phase epitaxy (SPE) and reactive deposition epitaxy (RDE). We have varied the thickness of the films, in order to study the magnetization and anisotropy evolution. A strongly enhanced magnetization of 1580 kA m-1, compared to 1200 ± 150 kA m-1for films grown on Ge(111), has been measured on ultrathin films of 5 nm grown by RDE. Thicker films exhibited magnetizations <750 kA m-1. The films grown by SPE also exhibit strong magnetization of 1490 kA m-1and a drop of magnetization by increasing the film thickness. The effective magnetic anisotropy exhibits a more complex behavior: increases on the SPE films and decreases on the RDE films while increasing the thickness of the films. Magnetostatic and interfacial anisotropies were considered and calculated. The results are discussed in terms of the growth methods and microstructure of the films.

Magneto-Transport Properties of Co-Cu Thin Films Obtained by Co-Sputtering and Sputter Gas Aggregation.

Cu100-xCox thin films have been obtained by sputtering (x = 3, 9) and sputter gas aggregation (x = 2.5, 7.5) and subsequent annealing at 400 °C for 1 h. We have studied their structural, magnetic, and magnetotransport properties, both for the as-deposited and annealed samples, confirming the important role of the fabrication method in the properties. The magnetic measurements and the fitting of the hysteresis loops evidence that as-deposited samples consist of superparamagnetic (SPM) and/or ferromagnetic clusters, but in the samples obtained by gas aggregation the clusters are greater (with ferromagnetic behavior at room temperature) whereas in the samples obtained by sputtering, the clusters are smaller and there are also diluted Co atoms in the Cu matrix. The annealing affects negligibly the samples obtained by gas aggregation, but the ones obtained by sputtering are more affected, appearing greater clusters. This behavior is also reflected in the magnetoresistance (MR) measurements of the samples, with different shapes of the MR curves depending on the preparation method: more lineal in the whole range for sputtering, saturation at low fields (about 10 kOe) for gas aggregation. Finally, a Kondo-like minimum in the resistance versus temperature is found in the samples obtained by sputtering, affected by the magnetic field and the annealing. The observed Kondo-like behavior and the influence of annealing on a Kondo-like minimum in sputtered thin films have been attributed to the presence of diluted Co atoms in the Cu matrix and the Co precipitations from the Co-Cu solid solution upon annealing respectively.