Exchange coupled bilayers of soft and hard ferromagnetic thin films show remarkable analogies to conventional antiferromagnetic/ferromagnetic exchange bias heterostructures. Not only do all these ferromagnetic bilayers exhibit a tunable exchange bias effect, they also show a distinct training behavior upon cycling the soft layer through consecutive hysteresis loops. In contrast with conventional exchange bias systems, such all ferromagnetic bilayer structures allow the observation of training induced changes in the bias-setting hardmagnetic layer by means of simple magnetometry. Our experiments show unambiguously that the exchange bias training effect is driven by deviations from equilibrium in the pinning layer. A comparison of our experimental data with predictions from a theory based upon triggered relaxation phenomena shows excellent agreement.

/pdf/exchange-bias-training-effect-in-coupled-all-ferromagnetic-3v67p955d1.pdf

Exchange bias training effect in coupled all ferromagnetic bilayer structures

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.

/pdf/enhancement-of-exchange-bias-and-perpendicular-magnetic-1i0bpa2q.pdf

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

Hot-deformed Nd-Fe-B magnets with a larger maximum energy product at higher operating temperature are desirable in a wide range of applications but are very challenging to realize in a common "single phase" structure. Here, we show the macroscopic structural design in hot-deformed magnets by using two kinds of melt-spun powders with/without heavy rare earth. Higher coercivity with a remarkably improved maximum energy product is obtained in the separated multilayer magnet. We find that the multilayer structure can improve the c-axis alignment of platelet-shaped grains in each layer and propose the possible interlayer's long-range magnetic interaction explaining the recoil loop open of designed magnets, coupled with visible field-induced domain evolution. This experimental approach reveals exciting applications of structural design in ultrafine-grained hot-deformed magnets. Published by AIP Publishing.

Hot-deformed Nd-Fe-B magnet with macroscopic composite structure

Investigation of dipolar interaction in FINEMET ribbons through longitudinally driven magneto-impedance effect

Reduction of shunt current in buffer-free IrMn based spin-valve structures

The effect of antiferromagnetic (AFM) layer on exchange bias (EB), training effect, and magnetotransport properties in ferromagnetic (FM) /AFM nanoscale antidot arrays and sheet films Ag(10 nm)/Co(8 nm)/NiO(tNiO)/Ag(5 nm) at 10 K is studied. The AFM layer thickness dependence of the EB field shows a peak at tNiO = 2 nm that is explained by using the random field model. The misalignment of magnetic moments in the three-dimensional antidot arrays causes smaller decrease of EB field compared with that in the sheet films for training effect. The anomalous magnetotransport properties, in particular positive magnetoresistance (MR) for antidot arrays but negative MR for sheet films are found. The training effect and magnetotransport properties are strongly affected by the three-dimensional spin-alignment effects in the antidot arrays.

Effect of antiferromagnetic layer thickness on exchange bias, training effect, and magnetotransport properties in ferromagnetic/antiferromagnetic antidot arrays

The magnetic properties and the possible interaction mechanisms of anisotropic soft- and hard-magnetic multilayers have been investigated by altering the thickness of different kinds of spacer layers The metal Ta and the insulating oxides MgO, Cr2O3 have been chosen as spacer layers to investigate the characteristics of the interactions between soft- and hard-magnetic layers in the anisotropic Nd-Dy-Fe-Co-B/α-Fe multilayer system The dipolar and exchange interaction between hard and soft phases are evaluated with the help of the first order reversal curve method The onset of the nucleation field and the magnetization reversal by domain wall movement are also evident from the first-order-reversal-curve measurements Reversible/irreversible distributions reveal the natures of the soft- and hard-magnetic components Incoherent switching fields are observed and the calculations show the semiquantitative contributions of hard and soft components to the system An antiferromagnetic spacer layer will weaken t

Magnetic interactions in anisotropic Nd-Dy-Fe-Co-B/α-Fe multilayer magnets

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Effect of antiferromagnetic layer thickness on exchange bias, training effect, and magnetotransport properties in ferromagnetic/antiferromagnetic antidot arrays

Magnetic interactions in anisotropic Nd-Dy-Fe-Co-B/α-Fe multilayer magnets