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International audience; rMn blocking temperature ($T_B$) is compared between IrMn/Co bilayers and (Pt/Co)$_3$/IrMn/Co and (Pd/Co)$_3$/IrMn/Co trilayers for different IrMn thicknesses. Exchange bias field ($H_{ex}$) is measured from 5 to 400 K. Trilayers show a more concave thermal decrease of $H_{ex}$($T$) compared to bilayers and, for thin IrMn layers, larger $T_B$ and sharper peak of coercive field Hc around $TB$. This $H_{ex}$($T$) behaviour presents improved characteristics for thermally assisted-MRAM (TA-MRAM) applications, with large $H_{ex}$/$H_c$ ratio. Two physical explanations are proposed: an indirect IrMn intergrain coupling through the (Pt(Pd)/Co)$_3$layer and a reduction of IrMn/Co interfacial coupling due to out-of-plane canting of the IrMn spins.

This paper is focused on thermally assisted magnetic random access memories (TA-MRAMs). It explains how the heating produced by Joule dissipation around the tunnel barrier of magnetic tunnel junctions (MTJs) can be used advantageously to assist writing in MRAMs. The main idea is to apply a heating pulse to the junction simultaneously with a magnetic field (field-induced thermally assisted (TA) switching). Since the heating current also provides a spin-transfer torque (current-induced TA switching), the magnetic field lines can be removed to increase the storage density of TA-MRAMs. Ultimately, thermally induced anisotropy reorientation (TIAR)-assisted spin-transfer torque switching can be used in MTJs with perpendicular magnetic anisotropy to obtain ultimate downsize scalability with reduced power consumption. TA writing allows extending the downsize scalability of MRAMs as it does in hard disk drive technology, but it also allows introducing new functionalities particularly useful for security applications (Match-in-Place™ technology).

A thermally assisted magnetoresistive random access memory device (TAS-MRAM) with reduced power for reading and writing; the memory device comprising a tunnel barrier 14 sandwiched between a ferromagnetic sense layer 16 and a ferromagnetic storage layer 12. An antiferromagnetic pinning layer 30 is disposed adjacent to the ferromagnetic storage layer 12. The pinning layer 30 pins a magnetic moment of the storage layer until heating is applied. Either or both of the storage and sense ferromagnetic layers includes a non-magnetic material to reduce the magnetization of the respective layers. The reduction in the storage layer magnetization and sense layer magnetization reduces the magnetostatic interaction between the storage layer and sense layer, resulting in less read/write power. The ferromagnetic materials in the sense and storage layers may include at least one of Co, Fe, Ni, and any alloy including Co, Fe, Ni, whilst the non-magnetic material includes at least one of Ta, Ti, Hf, Cr, Nb, Mo, Zr and any alloy containing Ta, Ti, Hf, Cr, Nb, Mo, Zr. The antiferromagnetic pinning layer may have a diameter less than 250nm based on the reduction in magnetization of at least one of the storage or sense layer. The ferromagnetic storage layer may be formed by sputtering ,chemical vapour (vapor) deposition CVD or physical vapour deposition PVD , and may involve co-sputtering the ferromagnetic and non magnetic material, or forming multi-layers of ferromagnetic and non magnetic material. The ferromagnetic sense layer may also be formed by co-sputtering of ferromagnetic and non magnetic material or forming multilayers of the two materials. An alternative embodiment (figures 7A/B) comprises a tunnel barrier layer 14 sandwiched between a ferromagnetic storage layer 16 and a synthetic antiferromagnetic storage layer 12, which includes a first ferromagnetic storage layer 11 adjacent to the tunnel barrier layer and a non magnetic coupling layer 15 sandwiched between the first ferromagnetic storage layer 11 and a second ferromagnetic storage layer 13. The alternative structure further allows for a relative increase in the thickness of the first ferromagnetic layer 11.