Modern computing technology is based on writing, storing and retrieving information encoded as magnetic bits. Although the giant magnetoresistance effect has improved the electrical read out of memory elements, magnetic writing remains the object of major research efforts. Despite several reports of methods to reverse the polarity of nanosized magnets by means of local electric fields and currents, the simple reversal of a high-coercivity, single-layer ferromagnet remains a challenge. Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay of data storage media, owing to their ability to retain a stable magnetization state over long periods of time and their amenability to miniaturization. However, the same anisotropy properties that make a material attractive for storage also make it hard to write to. Here we demonstrate switching of a perpendicularly magnetized cobalt dot driven by in-plane current injection at room temperature. Our device is composed of a thin cobalt layer with strong perpendicular anisotropy and Rashba interaction induced by asymmetric platinum and AlOx interface layers. The effective switching field is orthogonal to the direction of the magnetization and to the Rashba field. The symmetry of the switching field is consistent with the spin accumulation induced by the Rashba interaction and the spin-dependent mobility observed in non-magnetic semiconductors, as well as with the torque induced by the spin Hall effect in the platinum layer. Our measurements indicate that the switching efficiency increases with the magnetic anisotropy of the cobalt layer and the oxidation of the aluminium layer, which is uppermost, suggesting that the Rashba interaction has a key role in the reversal mechanism. To prove the potential of in-plane current switching for spintronic applications, we construct a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures. This device is simple, scalable and compatible with present-day magnetic recording technology.

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We demonstrate that the effective magnetic anisotropy of sputtered (Co/Pt) multilayers can be doubled by limiting the interdiffusion occurring at Co/Pt interfaces. We present a way to decrease the interdiffusion by inserting an ultra-thin Cu layer at or near the Co/Pt interfaces. When such a material is sputtered on Co prior to the Pt deposition, the perpendicular magnetic anisotropy, as well as the thermal stability, is enhanced for Co layer thicknesses smaller than 1 nm. This is of great interest for out-of-plane magnetized spintronic devices which require high perpendicular magnetic anisotropy for down-size scalability reasons together with a free layer as thin as possible to reduce the writing energy when switched by spin transfer torque.

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International audienc

A method to switch the magnetization of the free layer in magnetic tunnel junctions with perpendicular anisotropy is demonstrated. It consists in assisting the spin transfer switching of the magnetization by a thermally induced reorientation of the free layer magnetic anisotropy from out-of-plane to in-plane. The junction temperature increase is due to the Joule dissipation around the tunnel barrier produced by the same pulse of current which generates the spin transfer torque. This magnetic reorientation allows the spin transfer torque efficiency to be maximal since the spin polarization of the current is perpendicular to the magnetization of the free layer. Such a thermally assisted switching allows designing highly down-size scalable magnetoresistive random access memory cells with improved write efficiency.

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.

This letter presents a study of perpendicular anisotropy in Co/Ni multilayers, which could constitute a thick polarizer in spin torque oscillators or a magnetic electrode in magnetic tunnel junctions (MTJ) with perpendicular anisotropy. Perfectly square perpendicular loops are observed for as-deposited Co/Ni multilayers with various sublayer thicknesses and bilayer repetition numbers using a Pt buffer layer. An anisotropy energy of 1.0 × 106 erg·cm−3 is obtained for 9 nm thick Co/Ni multilayers. For Co/Ni multilayers deposited on MgO, no perpendicular magnetization component is observed in the as-deposited state, but it develops (even in 2.1 nm Co/Ni multilayers) after annealing at 250 °C.