Strain-controlled domain wall injection into nanowires for sensor applications

Abstract

We investigate experimentally the effects of strain on the injection of 180° domain walls (DWs) from a nucleation pad into magnetic nanowires, as typically used for DW-based sensors. In our study, the strain, generated by substrate bending, induces in the material a uniaxial anisotropy due to magnetoelastic coupling. To compare the strain effects, Co40Fe40B20, Ni, and Ni82Fe18 samples with in-plane magnetization and different magnetoelastic coupling are deposited. In these samples, we measure the magnetic field required for the injection of a DW, by imaging using differential contrast in a magneto-optical Kerr microscope. We find that strain increases the DW injection field and that the switching mechanism depends strongly on the strain direction. We observe that low magnetic anisotropy facilitates the creation of a domain wall at the junction between the pad and the wire, whereas a strain-induced magnetic easy axis significantly increases the coercive field of the nucleation pad. Moreover, we find that these effects of strain-induced anisotropy can be counteracted by an additional magnetic uniaxial anisotropy perpendicular to the strain-induced easy axis. We perform micromagnetic simulations to support the interpretation of our experimental findings showing that the above described observations can be explained by the effective anisotropy in the device. The anisotropy influences the switching mechanism in the nucleation pad as well as the pinning of the DW at the wire entrance. As the DW injection is a key operation for sensor performances, the observations show that strain is imposing a lower limit for the sensor field operating window.

Optimization of Permalloy properties for magnetic field sensors using He$^+$ irradiation

“…as-deposited 0.95(1) 78( 5 To apply strain to our devices, the substrate was bent mechanically with a three-point bending method. As reported in our previous work 34 a tensile and uniaxial strain is generated 35 . Moreover the strain is uniform in the central area of the sample and thus in the measured region.…”

“…Uniaxial in-plane strain is applied to a full film of NiFeCr(5 nm)/Ni 81 Fe 19 (30 nm)/Ta(4 nm) by three point bending method as previously reported 34 . Since the magnetization is coupled to the external strain via the expression of the anisotropy energy, the magnetic anisotropy before and after the application of strain is measured using Kerr microscopy.…”

Dynamic behavior of skyrmion collision: spiral and breath

“…In recent years, different topological magnetic structures such as domain walls [1][2][3], skyrmions [4][5][6][7], merons [8,9], bubbles [10], and vortexes [11,12] have been discovered in ferromagnetic thin-films. The emergence of these topological solitons is particularly important for the development of magnetic storage and spintronic devices [13][14][15][16][17][18][19][20][21].…”

Current-driven periodic domain walls injection in a ferromagnetic nanostrip with a modified perpendicular magnetic anisotropy region

“…The possibility of manipulating the DWs in ferromagnetic nanowires is * Authors to whom any correspondence should be addressed. of importance in magnetics because of its potential applications in future spin devices, such as memories, logic elements, sensors, and radio-frequency generators, and even in spin-wave channel transmission devices [1][2][3][4][5][6]. The realization of such devices depends in part on the control, manipulation, and movement of the DWs.…”