arXiv subjects

Russell P. Cowburn

Publications and source records attributed to Russell P. Cowburn.

8 recordsLinked to original sources

arXiv2020

Non-planar geometrical effects on the magnetoelectrical signal in a three-dimensional nanomagnetic circuit

Expanding nanomagnetism and spintronics into three dimensions (3D) offers great opportunities for both fundamental and technological studies. However, probing the influence of complex 3D geometries on magnetoelectrical phenomena poses important experimental and theoretical challenges. In this work, we investigate the magnetoelectrical signals of a ferromagnetic 3D nanodevice integrated into a microelectronic circuit using direct-write nanofabrication. Due to the 3D vectorial nature of both electrical current and magnetisation, a complex superposition of several magnetoelectrical effects takes place. By performing electrical measurements under the application of 3D magnetic fields, in combination with macrospin simulations and finite element modelling, we disentangle the superimposed effects, finding how a 3D geometry leads to unusual angular dependences of well-known magnetotransport effects such as the anomalous Hall effect. Crucially, our analysis also reveals a strong role of the noncollinear demagnetising fields intrinsic to 3D nanostructures, which results in an angular dependent magnon magnetoresistance contributing strongly to the total magnetoelectrical signal. These findings are key to the understanding of 3D spintronic systems and underpin further fundamental and device-based studies.

cond-mat.mes-hall↗

arXiv2018

Symmetry-Breaking Interlayer Dzyaloshinskii-Moriya Interactions in Synthetic Antiferromagnets

The magnetic interfacial Dzyaloshinskii-Moriya interaction (DMI) in multi-layered thin films can lead to exotic chiral spin states, of paramount importance for future spintronic technologies. Interfacial DMI is normally manifested as an intralayer interaction, mediated via a paramagnetic heavy metal in systems lacking inversion symmetry. Here we show how, by designing synthetic antiferromagnets with canted magnetization states, it is also possible to observe interfacial interlayer-DMI at room temperature. The interlayer-DMI breaks the symmetry of the magnetic reversal process via the emergence of noncollinear spin states, which results in chiral exchange-biased hysteresis loops. This work opens up yet unexplored avenues for the development of new chiral spin textures in multi-layered thin film systems.

cond-mat.mes-hall↗

arXiv2016

Nano scale thermo-electrical detection of magnetic domain wall propagation

In magnetic nanowires with perpendicular magnetic anisotropy (PMA) magnetic domain walls (DW) are narrow and can move rapidly driven by current induced torques. This enables important applications like high-density memories for which the precise detection of the position and motion of a propagating DW is of utmost interest. Today's DW detection tools are often limited in resolution, or acquisition speed, or can only be applied on specific materials. Here, we show that the anomalous Nernst effect provides a simple and powerful tool to precisely track the position and motion of a single DW propagating in a PMA nanowire. We detect field and current driven DW propagation in both metallic heterostructures and dilute magnetic semiconductors over a broad temperature range. The demonstrated spatial resolution below 20 nm is comparable to the DW width in typical metallic PMA systems.

cond-mat.mes-hall↗

arXiv2014

Resonance in Magnetostatically Coupled Transverse Domain Walls

We have observed the eigenmodes of coupled transverse domain walls in a pair of ferromagnetic nanowires. Although the pair is coupled magnetostatically, its spectrum is determined by a combination of pinning by edge roughness and dipolar coupling of the two walls. Because the corresponding energy scales are comparable, the coupling can be observed only at the smallest wire separations. A model of the coupled wall dynamics reproduces the experiment quantitatively, allowing for comparisons with the estimated pinning and domain wall coupling energies. The results have significant implications for the dynamics of devices based on coupled domain walls.

cond-mat.mtrl-sci↗

arXiv2009

Macrospin limit and configurational anisotropy in nanoscale Permalloy triangles

In Permalloy submicron triangles, configurational anisotropy - a higher-order form of shape anisotropy - yields three equivalent easy axes, imposed by the structures' symmetry order. Supported by micromagnetic simulations, an experimental method was devised to evaluate the nanostructure dimensions for which a Stoner-Wohlfarth type of reversal could be used to describe this particular magnetic anisotropy. In this regime, a straightforward procedure using an in-plane rotating field allowed us to quantify experimentally the six-fold anisotropy fields for triangles of different thicknesses and sizes.

cond-mat.mtrl-sci↗

arXiv2009

Six-fold configurational anisotropy and magnetic reversal in nanoscale Permalloy triangles

Six-fold configurational anisotropy was studied in Permalloy triangles, in which the shape symmetry order yields two energetically non-degenerate micromagnetic configurations of the spins, the so-called "Y" and "buckle" states. A twelve pointed switching astroid was measured using magneto-optical experiments and successfully reproduced numerically, with different polar quadrants identified as specific magnetic transitions, thereby giving a comprehensive view of the magnetic reversal in these structures. A detailed analysis highlighted the necessity to include the physical rounding of the structures in the simulations to account for the instability of the Y state.

cond-mat.mtrl-sci↗

arXiv2008

Domain wall pinning and potential landscapes created by constrictions and protrusions in ferromagnetic nanowires

The potential experienced by transverse domain walls (TDWs) in the vicinity of asymmetric constrictions or protrusions in thin Permalloy nanowires is probed using spatially resolved magneto-optical Kerr effect measurements. Both types of traps are found to act as pinning centers for DWs. The strength of pinning is found to depend on the trap type as well as on the chirality of the incoming DW; both types of traps are seen to act either as potential wells or potential barriers, also depending on the chirality of the DW. Micromagnetic simulations have been performed that are in good qualitative agreement with the experimental results.

cond-mat.mtrl-sci↗

arXiv2003

Domain wall propagation in magnetic nanowires by spin polarized current injection

We demonstrate movement of a head-to-head domain wall through a magnetic nanowire simply by passing an electrical current through the domain wall and without any external magnetic field applied. The effect depends on the sense and magnitude of the electrical current and allows direct propagation of domain walls through complex nanowire shapes, contrary to the case of magnetic field induced propagation. The efficiency of this mechanism has been evaluated and the effective force acting on the wall has been found equal to 0.88x10-9 N.A-1.

cond-mat.mtrl-sci↗