Diffusive model of current-in-plane-tunneling in double magnetic tunnel junctions

We propose a model that describes current-in-plane tunneling transport in double barrier magnetic tunnel junctions in diffusive regime. Our study shows that specific features appear in double junctions that are described by introducing two typical length scales. The model may be used to measure the magnetoresistance and the resistance area product of both barriers in unpatterned stacks of double barrier magnetic tunnel junctions.Comment: 4 pages, 3 figure

Analysis of anisotropy crossover due to oxygen in Pt/Co/MOx trilayer

Extraordinary Hall effect and X-ray spectroscopy measurements have been performed on a series of Pt/Co/MOx trilayers (M=Al, Mg, Ta...) 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 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

Étude de plasmas générés par laser, soumis à des champs magnétique et électrique. Utilisation possible en techniques de dépôts.

The properties of laser generated plasmas have been studied. In the considered experimental conditions and for all studied elements (Al, Cu, Fe, Mo, Pt), the majority of the evaporated species are ions, with typical energies in the range 60 eV - 100 eV. Due to excitation and recombination mechanisms, the adiabatic constant which governs expansion (temperature, angular distribution) is around 1.2, less than the value 5/3 expected for a monoatomic gas. Strong plasma confinement is obtained under a magnetic field, B, of up to 5 T. The initial plasma temperature then deduced is of the order of 100000 K. To first order, the ion energy distribution is not affected by the field. Due to the high plasma density resulting from confinement, recombination effects are significant. An original approach for the preparation of directly structured materials has been proposed which associates the effects of magnetic and electric fields on plasmas.Les propriétés de plasmas générés par laser ont été étudiées. Dans nos conditions expérimentales et quelques soient les éléments analysés (Al, Cu, Fe, Mo, Pt), la majorité des espèces évaporées sont des ions, d'énergies typiques de 60 eV à 100 eV. Du fait des mécanismes d'excitation et recombinaison, la constante adiabatique qui gouverne la détente du plasma (température, distribution angulaire) est de l'ordre de 1.2, inférieure à la valeur 5/3 caractéristique d'un gaz monoatomique. Un fort confinement du plasma est obtenu sous un champ magnétique, B, jusqu'à 5 T. La température initiale du plasma alors déduite est de l'ordre de 100000 K. Au premier ordre, la distribution énergétique n'est pas modifiée par le champ. Du fait de la forte densité du plasma résultant du confinement, les phénomènes de recombinaison ne sont pas négligeables. Une méthode originale d'élaboration de dépôts directement structurés a été proposée, associant les effets combinés, sur un plasma, de champs magnétique et électrique

Etude de plasmas générés par laser, soumis à des champs magnétique et électrique (utilisation possible en techniques de dépôts)

Les propriétés de plasmas générés par laser ont été étudiées. Dans nos conditions expérimentales et quelques soient les éléments analysés (Al, Cu, Fe, Mo, Pt), la majorité des espèces évaporées sont des ions, d'énergies typiques de 60 eV à 100 eV. Du fait des mécanismes d'excitation et recombinaison, la constante adiabatique qui gouverne la détente du plasma (température, distribution angulaire) est de l'ordre de 1.2, inférieure à la valeur 5/3 caractéristique d'un gaz monoatomique. Un fort confinement du plasma est obtenu sous un champ magnétique, B, jusqu'à 5 T. La température initiale du plasma alors déduite est de l'ordre de 105 K. Au premier ordre, la distribution énergétique n'est pas modifiée par le champ. Du fait de la forte densité du plasma résultant du confinement, les phénomènes de recombinaison ne sont pas négligeables. Une méthode originale d'élaboration de dépôts directement structurés a été proposée, associant les effets combinés, sur un plasma, de champs magnétique et électrique.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Influence of a Ta spacer on the magnetic and transport properties of perpendicular magnetic tunnel junctions

International audienceUltrathin Ta layers were inserted in the bottom hard (Co/Pt)/Ta/CoFeB/MgO magnetic electrode of perpendicular magnetic tunnel junctions. The magnetization of the top part of this electrode abruptly falls in-plane when the Ta thickness exceeds 0.45 nm. This results from the balance between the various energy terms acting on this layer (exchange-like coupling through Ta, demagnetizing energy, and perpendicular anisotropy at the CoFeB/MgO interface). For small Ta thicknesses, this insertion leads to a strong improvement of the tunnel magnetoresistance, as long as the magnetization of all layers remains perpendicular-to-plane

Enhanced annealing stability and perpendicular magnetic anisotropy in perpendicular magnetic tunnel junctions using W layer

International audienceThe magnetic properties of the perpendicular storage electrode (buffer/MgO/FeCoB/Cap) were studied as a function of annealing temperature by replacing Ta with W and W/Ta cap layers with variable thicknesses. W in the cap boosts up the annealing stability and increases the effective perpendicular anisotropy by 30% compared to the Ta cap. Correspondingly, an increase in the FeCoB critical thickness characterizing the transition from perpendicular to in-plane anisotropy was observed. Thicker W layer in the W(t)/Ta 1 nm cap layer makes the storage electrode highly robust against annealing up to 570 °C. The stiffening of the overall stack resulting from the W insertion due to its very high melting temperature seems to be the key mechanism behind the extremely high thermal robustness. The Gilbert damping constant of FeCoB with the W/Ta cap was found to be lower when compared with the Ta cap and stable with annealing. The evolution of the magnetic properties of bottom pinned perpendicular magnetic tunnel junctions (p-MTJ) stack with the W2/Ta1 nm cap layer shows back-end-of-line compatibility with increasing tunnel magnetoresistance up to the annealing temperature of 425 °C. The pMTJ thermal budget is limited by the synthetic antiferromagnetic hard layer which is stable up to 425 °C annealing temperature while the storage layer is stable up to 455 °C

Modulation of spin transfer torque amplitude in double barrier magnetic tunnel junctions

International audienceMagnetization switching induced by spin transfer torque is used to write magnetic memories (Magnetic Random Access Memory, MRAM) but can be detrimental to the reading process. It would be quite convenient therefore to modulate the efficiency of spin transfer torque. A solution is adding an extra degree of freedom by using double barrier magnetic tunnel junctions with two spin-polarizers, with controllable relative magnetic alignment. We demonstrate, for these structures, that the amplitude of in-plane spin transfer torque on the middle free layer can be efficiently tuned via the magnetic configuration of the electrodes. Using the proposed design could thus pave the way towards more reliable read/write schemes for MRAM. Moreover, our results suggest an intriguing effect associated with the out-of-plane (field-like) spin transfer torque, which has to be further investigated. (C) 2015 AIP Publishing LLC

High sensitivity magnetic field sensor for spatial applications

International audienceA high sensitivity 1D magnetic field sensor is developed for spatial applications, in order to replace the heavy search-coils currently used. This new sensor combines a flux concentrator, biasing coils for field modulation and magnetic tunnel junctions. These three elements are fabricated and independently characterized. Finally, the expected performance of a sensor combining these three elements can be estimated

Reduced Thermal Variation of Perpendicular Magnetic Anisotropy in Magnetically Stiffened Dual-W Composite Storage Layer for Spin-Transfer-Torque Magnetic Random-Access Memory

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Spin Electronics Correlation Between Disordered Magnetic Phases in Ferromagnetic/Antiferromagnetic Thin Films and Device-to-Device Variability of Exchange Bias in Spintronic Applications

Abstract-Spintronic applications rely on ferromagnetic/antiferromagnetic exchange biased bilayers. In this study, we show whether and how disordered magnetic phases, which exhibit low freezing temperatures and are located in the ferromagnetic/antiferromagnetic thin film, affect the device-to-device variability of exchange bias in magnetic applications once the film is nanofabricated. Index Terms-Spin electronics, disordered magnetic phases, exchange bias, device variability, magnetic random-access memory, blocking temperature distribution