Magnetoresistive sensors based on the elasticity of domain walls

Magnetic sensors based on the magnetoresistance effects have a promising application prospect due to their excellent sensitivity and advantages in terms of the integration. However, competition between higher sensitivity and larger measuring range remains a problem. Here, we propose a novel mechanism for the design of magnetoresistive sensors: probing the perpendicular field by detecting the expansion of the elastic magnetic Domain Wall (DW) in the free layer of a spin valve or a magnetic tunnel junction. Performances of devices based on this mechanism, such as the sensitivity and the measuring range can be tuned by manipulating the geometry of the device, without changing the intrinsic properties of the material, thus promising a higher integration level and a better performance. The mechanism is theoretically explained based on the experimental results. Two examples are proposed and their functionality and performances are verified via micromagnetic simulation.Comment: 4 figures, 13 page

Control of magnetoelastic coupling in Ni/Fe multilayers using He+ ion irradiation

This study reports the effects of post-growth He+ irradiation on the magneto-elastic properties of a Ni/Fe multi-layered stack. The progressive intermixing caused by He+ irradiation at the interfaces of the multilayer allows us to tune the saturation magnetostriction value with increasing He+ fluences and even to induce a reversal of the sign of the magnetostrictive effect. Additionally, the critical fluence at which the absolute value of the magnetostriction is dramatically reduced is identified. Therefore, insensitivity to strain of the magnetic stack is nearly reached, as required for many applications. All the above-mentioned effects are attributed to the combination of the negative saturation magnetostriction of sputtered Ni and Fe layers and the positive magnetostriction of the NixFe1-x alloy at the intermixed interfaces, whose contribution is gradually increased with irradiation. Importantly, the irradiation does not alter the layer polycrystalline structure, confirming that post-growth He+ ion irradiation is an excellent tool to tune the magneto-elastic properties of multilayer samples. An alternative class of spintronic devices can be envisioned with a material treatment able to arbitrary change the magnetostriction with ion-induced "magnetic patterning.

Voltage control of magnetism in ferromagnetic structures (Conference Paper)

San Diego, California, United StatesInternational audienceUntil now, spintronics devices have relied on polarized currents, which still generate relatively high dissipation, particularly for nanodevices based on DW motion. A novel solution to further reduce power consumption is emerging, based on electric field (E) gating to control the magnetic state. Here, we will describe the state of the art and our recent experiments on voltage induced changes in the magnetic properties of ferromagnetic metals. A thorough description of the advances in terms of control of intrinsic properties such as magnetic anisotropy and ferromagnetic transition temperature as well as in intrinsic properties like coercive field and domain wall motion will be presented. Additionally, a section will be dedicated to the summary of the key aspects concerning the fabrication and performance of magneto-electric field-effect devices

Tuning the magnetodynamic properties of all-perpendicular spin valves using He+ irradiation

Using He+ ion irradiation, we demonstrate how the magnetodynamic properties of both ferromagnetic layers in all-perpendicular [Co/Pd]/Cu/[Co/Ni] spin valves can be tuned by varying the He+ ion fluence. As the perpendicular magnetic anisotropy of both layers is gradually reduced by the irradiation, different magnetic configurations can be achieved from all-perpendicular (up arrow up arrow), through orthogonal (->up arrow), to all in-plane (paired right arrows). In addition, both the magnetic damping (alpha) and the inhomogeneous broadening (Delta H-0) of the Co/Ni layer improve substantially with increasing fluence. While the GMR of the spin valve is negatively affected, decreasing linearly from an original value of 1.14% to 0.4% at the maximum fluence of 50x10(14) He+/cm(2), most of the Co/Ni layer improvement is achieved already at a fluence of 10x10(14) He+/cm(2), for which GMR only reduces to 0.9%

Suppression of all-optical switching in He +-irradiated Co/Pt multilayers: influence of the domain-wall energy

International audienceThe observation of all-optical helicity-dependent switching (AO-HDS) in ferri- and ferro-magnetic materials depends not only on the saturation magnetization, but on the magnetic domain size which takes into account the competition between the demagnetizing energy and the domain wall (DW) energy. In this paper, we study the optical response of Co/Pt multilayers for which perpendicular magnetic anisotropy can be tuned using He+ -irradiation. This allows us to correlate the observation of AO-HDS with the magnetic properties of the He+ -irradiated multilayer. These results give direct evidence of the crucial role of the DW energy in the laser-induced switching process