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A model of exchange bias in a polycrystalline bilayer based on thermal fluctuations was extended to account for an arbitrary magnetization angle of the ferromagnetic (FM) layer. It allows for a more accurate description of the thermally activated reversal of the Néel vector in antiferromagnetic (AFM) grains since the extended model takes into account the variation of barrier height resulting from the magnetization angle of the FM layer. Field-annealing (setting of the exchange bias) and further relaxation of the FM/AFM bilayer was simulated using a sequence of iterations based on this model. An array of AFM grains is generated based on a lognormal distribution of their volume. Chosen parameters of distribution are based on the fit to the experimentally measured temperature dependence of exchange bias in sputter-deposited CoFe/IrMn films. The angular deviation of the exchange bias and the degradation of its amplitude in an applied field, with relative angle varied from 0° to 180°, are calculated. Hysteresis of the exchange bias with field exposure is observed. A temperature–time ($T$ – $\tau$) diagram of the deviation angle, predicting the stability of the exchange bias under specific temperature and time, is presented. [ABSTRACT FROM AUTHOR]

We report spin transport in CVD graphene-based lateral spin valves using different magnetic contacts. We compared the spin signal amplitude measured on devices where the cobalt layer is directly in contact with the graphene to the one obtained using tunnel contacts. Although a sizeable spin signal (up to ∼2 Ω) is obtained with direct contacts, the signal is strongly enhanced (∼400 Ω) by inserting a tunnel barrier. In addition, we studied the resistance-area product (R.A) of a variety of contacts on CVD graphene. In particular, we compared the R.A products of alumina and magnesium oxide tunnel barriers grown by sputtering deposition of aluminum or magnesium and subsequent natural oxidation under pure oxygen atmosphere or by plasma. When using an alumina tunnel barrier on CVD graphene, the R.A product is high and exhibits a large dispersion. This dispersion can be highly reduced by using a magnesium oxide tunnel barrier, as for the R.A value. This study gives insight in the material quest for reproducible and efficient spin injection in CVD graphene. [ABSTRACT FROM AUTHOR]

Extraordinary Hall effect and x-ray spectroscopy measurements have been performed on a series of Pt/Co/MOx trilayers (M=Al, Mg, Ta, etc.) in order to investigate the role of oxidation in the onset of perpendicular magnetic anisotropy at the Co/MOx interface. It is observed that varying the plasma oxidation time modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. We focused on the influence of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The interfacial electronic structure is analyzed via x-ray photoelectron spectroscopy measurements. It is shown that the maximum of out-of-plane magnetic anisotropy corresponds to the appearance of a significant density of Co–O bondings at the Co/AlOx interface. [ABSTRACT FROM AUTHOR]

Several investigations are conducted to study the metallic Mg insertions taking place in rf deposited MgO barrier of magnetic tunnel junctions structure. A tope Mg insertion is shown to lead to lower tunnel magnetoresistance in the structures.

The various mechanisms associated with the off-axis deposition of the Al layer for the low resistance tunnel barrier are discussed. The off-axis method is shown to be extremely beneficial for enhancing the magnetic, as well as electrical properties of the alumina.

Several analyses are conducted to explain the effects of heating pulse width and antiferromagent thickness on the write power density of the IrMn and FeMn compounds. Lower thickness is shown to lead to low write power density.

The magnetic switching of the exchange biased storage layer in thermally assisted magnetic random access memory cells is studied in the nanosecond time domain. The probability of switching versus pulse duration has displayed characteristic periodic steps, which are attributed to a combined effect of the applied field and spin transfer produced by the heating current pulses.

The preparation and magnetic properties of submicron magnetic tunnel junctions (MTJs) are described by using magnetic electrodes based on Co/Pt multilayers displaying perpendicular magnetic anisotropy (PMA) on both sides of an alumina barrier. The magnetic moments of both electrodes are shown to be out of plane and two well-separated switching fields are used for obtaining the well-defined parallel and antiparallel configurations of the magnetizations.

The role of interfacial oxidation in the anisotropy crossover of a thin Co layer in Pt/Co/Al[O.sub.x] sandwiches are examined. The studies have shown that increasing the oxidation time increases the amount of interfacial oxide, which is at the origin at perpendicular magnetic anisotropy.

Spintronics devices and in particular thermally assisted magnetic random access memories require a wide range of ferromagnetic/antiferromagnetic (F/AF) exchange bias (EB) properties and subsequently of AF materials to fulfil diverse functionality requirements for the reference and storage. For the reference layer, large EB energies and high blocking temperature (TB) are required. In contrast, for the storage layer, mostly moderate TB are needed. One of the present issues is to find a storage layer with properties intermediate between those of IrMn and FeMn and in particular: (i) with a TB larger than FeMn for better stability at rest-T but lower than IrMn to reduce power consumption at write-T and (ii) with improved magnetic interfacial quality, i.e., with reduced interfacial glassy character for lower properties dispersions. To address this issue, the EB properties of F/AF based stacks were studied for various mixed [IrMn/FeMn] AFs. In addition to EB loop shifts, the F/AF magnetic interfacial qualities and the AF grains thermal stability are probed via measurements of the low- and high-temperature contributions to the TB distributions, respectively. A tuning of the above three parameters is observed when evolving from IrMn to FeMn via [IrMn/FeMn] repetitions. [ABSTRACT FROM AUTHOR]

X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlOx trilayers to investigate the role of Co oxidation in the perpendicular magnetic anisotropy at the Co/AlOx interface. It is observed that varying the degree of oxidation modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. The microscopic structural properties are analyzed via x-ray photoelectron spectroscopy measurements. It is shown that increasing the oxidation time enhances the amount of interfacial oxide, which may be at the origin of perpendicular magnetic anisotropy. [ABSTRACT FROM AUTHOR]