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Presents information on a study which described an analytical calculation of the magnetoresistive (MR) response of spin-valve structures with synthetic antiferromagnetic pinned (AP) layer. Semiclassical calculation of the giant MR amplitude in spin valves with synthetic AP layers; Results and discussion; Conclusions.

The magnetic switching of the exchange biased storage layer in thermally assisted magnetic random access memory cells has been studied in the nanosecond time domain. Under reversed static external field, the magnetic tunnel junctions (MTJs) were subjected to current heating pulses long enough to heat the structure above the blocking temperature of the antiferromagnetic layer. The magnetic response of the storage layer was characterized by single-shot real-time measurement of MTJ resistance. The switching of the storage layer exhibits stochastic fluctuations. Nevertheless, using a heating current density of 4.7×106 A/cm2 corresponding to a bias voltage of 1.8 V, the switching takes place in less than 4 ns under 5 mT. Interestingly, the probability of switching versus pulse duration exhibits characteristic periodic steps which are ascribed to a combined effect of the applied field and spin transfer produced by the heating current pulses. [ABSTRACT FROM AUTHOR]

Exchange bias effects have been observed in an array of submicron antiferromagnetic-ferromagnetic dots prepared by nanosphere lithography. The angular dependences of the exchange bias field HE, coercivity HC, and squareness ratio MR/MS of the array of dots have been measured and compared with those of a continuous film prepared under the same conditions. An HE enhancement of around 30% is observed along the field-cooling direction in the dots. The possible mechanisms responsible for this enhancement are discussed. Moreover, magnetic imaging reveals that complex magnetization reversal mechanisms occur in the nanostructures, which cause significant differences in the shape of the hysteresis loops, when compared to the exchange biased continuous films. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, exchange bias was used as a probe to characterise the temperature profile induced by the inelastic relaxation of electrons tunnelling across a MgO barrier. Thermally assisted magnetic random access memory (TA-MRAM) cells comprising a magnetic tunnel junction (MTJ) with a reference pinned layer and a FeMn exchange biased storage layer were used. The pinning direction of the ferromagnetic storage layer is reversed when heated above the blocking temperature of the antiferromagnetic layer (FeMn). The power density required to reach this blocking temperature in the FeMn layer depends on the current polarity, indicating that the heat source term associated with the current flowing through the barrier depends itself on the current direction in contrast to simple Joule heating. This effect is due to the mechanism of energy dissipation in tunnelling. The tunnelling itself is ballistic i.e., without dissipation. However, after tunnelling, the hot electrons very quickly relax to the Fermi energy thereby loosing their excess energy in the receiving electrode. Therefore, the heat is essentially generated on one side of the barrier so that the whole profile of temperature throughout the pillar depends on the current direction. Full 3D thermal simulations also confirmed the temperature profile asymmetry. The proper choice of heating current direction (i.e., voltage polarity applied to the MTJ) can yield a reduction of about 10% in the heating power density required to enable writing in thermally assisted MRAM cells. [ABSTRACT FROM AUTHOR]

Presents a study which investigated the magnetic properties of (plutonium--cobalt)[subn] multilayers covered by an antiferromagnetic iron manganese layer. Experimental technique; Magnetic properties; Conclusion.

We demonstrate by macrospin simulations that in a spin-torque nano-oscillator having synthetic antiferromagnet fixed layer, the non-conservative dynamic coupling between the free and fixed layers caused by spin-torque effect leads to a substantial reduction of the linewidth of the current-induced spin wave mode, involving oscillations in all three magnetic layers. By analysing the phase and amplitude noise extracted from the simulated signal, we prove that the obtained linewidth reduction is related to the reduction of the dimensionless non-linear amplitude-phase coupling parameter ν. [ABSTRACT FROM AUTHOR]

The coherence of the precessional switching was compared in planar spin-valves comprising either an additional simple perpendicular polarizer or a synthetic antiferromagnet perpendicular polarizer. A significant improvement in the precession coherence was observed experimentally in the second type of samples. Micromagnetic simulations were performed to study the effect of the stray field from the perpendicular polarizer. They provide an explanation for the gradual loss of coherence of the precession in terms of vortex formation, which occurs much faster when a simple perpendicular polarizer is used. [ABSTRACT FROM AUTHOR]

Using a top-down approach, synthetic antiferromagnetic micro/nanoparticles usable for biological applications were prepared. These particles exhibit 'superparamagneticlike' properties. Their magnetic susceptibility can be accurately controlled by the thickness of the constituting layers. When dispersed in solution, striking differences in their interactions are observed depending on their susceptibility. Above a susceptibility threshold, a phenomenon of self-polarization is observed in zero applied field, resulting in a gradual agglomeration of the particles. In contrast, below the susceptibility threshold, the particles get redispersed in zero field. This is interpreted by a self-consistent model taking into account dipolar interactions between particles and their magnetic susceptibility. [ABSTRACT FROM AUTHOR]

For ferromagnetic (F)/antiferromagnetic (AF) nanodots contributions of AF spins to exchange bias is discussed. The relative weights of AF entities located at the dot edges, at the F/AF interface and in the AF grains were obtained by comparing the blocking temperature distribution of an array of nanodots with that of corresponding continuous film. Due to grain cutting, the grain size distribution is altered. We show here that the dot edges constitute additional locations for the formation of spin-glasslike AF regions at the F/AF interface. The result of patterning is thus twofold and weakens the dot ability to resist thermally activated magnetization reversal. [ABSTRACT FROM AUTHOR]

The magnetic properties of perpendicular exchange biased ferromagnetic (FM)/antiferromagnetic (AFM) [Pt/Co]n/IrMn systems were investigated by a new set-up combining element-selective soft x-ray holography and spectroscopy measurements. The holography experiments allow imaging the magnetization reversal of an exchange biased FM layer with an equivalent Co thickness below 5 nm in real space and in external magnetic fields, and provide direct evidence of its asymmetric nature. From the spectroscopy analysis, we have quantified the unpinned (pinned) uncompensated AFM moments, providing direct evidence of its parallel (antiparallel) alignment with respect to the FM moments. [ABSTRACT FROM AUTHOR]

Spin polarized current induced self oscillations have been investigated in both the free layer and the synthetic antiferromagnetic (SAF) pinned layer of spin valve nanopillars. Compared with free layer excitations, the acoustic type SAF excitations are characterized by high emitted power and much narrower linewidth. Furthermore, in contrast to free layer excitations, the SAF in-plane precession mode exhibits an unexpected crossover from redshift (df/dI<0) to blueshift (df/dI>0) in frequency f versus current I as the in-plane magnetic field is increased. From simulations we identify this crossover as a signature of large amplitude spin current induced precessional dynamics in the SAF. [ABSTRACT FROM AUTHOR]

We present a study of exchange bias in ferromagnet/antiferromagnet/ferromagnet (FM/AFM/FM) trilayers, with in-plane and out-plane easy axes. Using element-specific x-ray magnetic circular dichroism, we demonstrate that simultaneous in-plane and out-of-plane exchange bias can be induced using a single antiferromagnet and zero field cooling, whereas field cooling only induces exchange bias to the layer with easy axis parallel to the cooling field. Our results further evidence the presence of pinned uncompensated moments in both the FM and AFM layers, implying that the AFM layer is capable of supporting uncompensated spins in two orthogonal directions at the same time. [ABSTRACT FROM AUTHOR]

The temperature dependence of the magnetic properties of [Pt/Co] multilayers (ML), exhibiting perpendicular anisotropy, with and without exchange biasing with an antiferromagnet (AFM) has been investigated. Upon heating, a loss of the out-of-plane anisotropy and, consequently, of the remanence to saturation ratio is observed in these systems. However, such effect occurs at higher temperatures in the [Pt/Co] ML exchange coupled to the AFM than for the unbiased ML. This is attributed to the additional anisotropy induced to the ML by the ferromagnetic-antiferromagnetic exchange coupling. [ABSTRACT FROM AUTHOR]

This paper reports sub-nanosecond precessional spin-transfer switching in elliptical magnetic tunnel junction nanopillars. This result is obtained in samples integrating a synthetic antiferromagnetic perpendicular polarizer and a tunnel junction with in-plane magnetized electrodes. The out-of-plane precession of the free layer magnetization results in oscillations of the switching probability as a function of the pulse width. At 9.25 MA/cm2 current density, these oscillations have a period of 1 ns with a high degree of coherence. [ABSTRACT FROM AUTHOR]

In (Pt/Co)[sub n]/FeMn multilayers, the magnitude of exchange bias, H[sub E], can be considerably enhanced by placing an ultrathin nonmagnetic Pt spacer between the multilayer (ML) and the antiferromagnetic (AFM) layer. The bias is maximum for a spacer layer thickness, t, of a few angstroms and it decreases progressively as t is further increased. This bias enhancement is accompanied by an increase of coercivity, H[sub C]. This behavior is due to the role of the Pt spacer in enhancing the perpendicular effective anisotropy of the last Co layer in the ML, which has the effect of increasing the net ferromagnetic (FM)/AFM spin projection, thus leading to the H[sub E] and H[sub C] enhancements. The decrease of H[sub E] and H[sub C] for thicker spacer layers is due to the limited range of the FM–AFM proximity effect. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Synthetic antiferromagnets are of great interest as reference layers in magnetic tunnel junctions since they allow decreasing the dipolar coupling between the two magnetic electrodes and exhibit larger pinning fields than single reference layers. In this letter, we investigate the effect of the insertion of an ultrathin Pt layer in contact with the Ru spacer in synthetic antiferromagnets with perpendicular magnetic anisotropy. Surprisingly, for Ru thickness below 0.75 nm, the antiferromagnetic coupling amplitude through Ru first increases upon Pt insertion up to a critical Pt thickness (∼0.25 nm) above which coupling decreases. In addition, the corresponding increase of perpendicular magnetic anisotropy enhances the thermal stability of the structure. [ABSTRACT FROM AUTHOR]

A correction to the publication date and the name of the author of the article "Direct evidence of imprinted vortex states in the antiferromagnet of exchange biased microdisks," that was published in the August 10, 2009 is presented.

Abstract: The interlayer exchange coupling between Co/Pt perpendicular-to-plane magnetized layers across a thin IrMn spacer layer was experimentally studied. In contrast to earlier studies on interlayer coupling through antiferromagnetic NiO, which revealed an oscillatory coupling behavior as a function of NiO thickness, a ferromagnetic coupling was observed here in the range of IrMn thickness between 0.6 and 1.5nm and antiferromagnetic between 1.5 and 2.5nm. The antiferromagnetic coupling is attributed to an orange peel magnetostatic mechanism whereas the ferromagnetic coupling is attributed to an out-of-plane polarization of the antiferromagnetic IrMn layer induced by the interfacial exchange interaction with the adjacent out-of-plane ferromagnetic layers. Measurements of hysteresis loops versus temperature show that the coupling vanishes at 510K for t IrMn=1nm. This critical temperature is far below the Néel temperature of bulk IrMn, but above the blocking temperature of IrMn/Co bilayers at such thickness. Using a one-dimensional model describing a partial domain wall in the antiferromagnet, we explain the coupling in terms of an out-of-plane tilt of the Mn moments at the IrMn/(Co/Pt) interfaces yielding a weak net polarization of the IrMn. Finally, the non-oscillatory decay of the coupling was attributed to the compensated spin structure of the IrMn in the parallel to the interfaces. [Copyright &y& Elsevier]