Optical-controlled domain wall resistance in magnetic nanojunctions

Domain walls in ferromagnetic metals are known to be a source of resistance. In the present work resistance of a domain wall in a ferromagnetic nanojunction is investigated using the semiclassical approach. The analysis is based on the Boltzmann transport equation, within the relaxation time approximation. The one-dimensional Néel-type magnetic domain wall is considered and the effect of the electron-photon interaction on the resistance is studied. The results indicate that polarization and wavelength of the photon play a significant role in the magnetoresistance. The resistance of the nanojunction decreases as the wavelength of the photon increases. It is also shown that the domain wall resistance decreases by increasing the Fermi energy.     

Individual domain wall resistance in submicron ferromagnetic structures

The resistance generated by individual domain walls is measured in a FePd nanostructure. Combining transport and magnetic imaging measurements, the intrinsic domain wall resistance is quantified. It is found positive and of a magnitude consistent with that predicted by models based on spin scattering effects within the walls. This magnetoresistance at a nanometer scale allows a direct counting of the number of walls inside the nanostructure. The effect is then used to measure changes in the magnetic configuration of submicron stripes under application of a magnetic field.     

Magnetic moment softening and domain wall resistance in Ni nanowires

We perform ab initio calculations of the electronic structure and conductance of atomic-size Ni nanowires with domain walls only a few atomic lattice constants wide. We show that the hybridization between noncollinear spin states leads to a reduction of the magnetic moments in the domain wall resulting in the enhancement of the domain wall resistance. Experimental studies of the magnetic moment softening may be feasible with modern techniques such as scanning tunneling spectroscopy.     

Magnetic field dependence of the domain wall resistance in a quantum wire

For an ideal one-dimensional ferromagnetic wire with a magnetic domain wall (DW), contribution of the DW to the resistivity of the system has been investigated. We have studied the resistance due to the magnetic impurities in the domain wall which was suspended in a weak magnetic field for two types of chiralities. The analysis has been based on Boltzmann transport equation, within the relaxation time approximation. Through this formalism, both increasing and decreasing of the resistance due to the DW have been predicted in presence of Zeeman interaction as an extrinsic mechanism.     

Current-induced domain wall motion

The present understanding of domain wall motion induced by spin-polarized electric current is assessed by considering a subset of experiments, analytical models, and numerical simulations based on an important model system: soft magnetic nanowires. Examination of this work demonstrates notable progress in characterizing the experimental manifestations of the “spin-torque” interaction, and in describing that interaction at a phenomenological level. At the same time, an experimentally verified microscopic understanding of the basic mechanisms will require substantial future efforts, both experimental and theoretical.     

Anisotropy of the electrical resistance of ferromagnetic metals

The spin-orbital mechanism of electron scattering in 3-d-ferromagnetic metals is reviewed on the basis of the two-zone model. It is shown that in the case of free s-electrons and strongly bound d-electrons it is the latter which have the predominant role in the anisotropy of the electrical resistance. It is indicated that to produce quantitative agreement with experiment account must be taken of the deviation of the s-electron wave functions from plane waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 7–12, July, 1972.     

Angular dependence of domain wall resistivity in artificial magnetic domain structures

We exploit the ability to precisely control the magnetic domain structure of perpendicularly magnetized Pt/Co/Pt trilayers to fabricate artificial domain wall arrays and study their transport properties. The scaling behavior of this model system confirms the intrinsic domain wall origin of the magnetoresistance, and systematic studies using domains patterned at various angles to the current flow are excellently described by an angular-dependent resistivity tensor containing perpendicular and parallel domain wall resistivities. We find that the latter are fully consistent with Levy-Zhang theory, which allows us to estimate the ratio of minority to majority spin carrier resistivities, rho downward arrow/rho upward arrow approximately 5.5, in good agreement with thin film band structure calculations.     

Transient dynamics of pinning of domain wall

We study the evolution of an elastic string, serving as model for a domain wall, into the pinned state at driving forces slightly below the depinning threshold force F_c. We quantify the temporal evolution of the string by an activity function A(t) representing the fraction of active nodes at time t and find three distinct dynamic regimes. There is an initial stage of fast decay of the activity; in the second, intermediate, regime, an exponential decay of activity is observed; and, eventually, the fast collapse of the string towards its final pinned state results in decay in the activity with A_r∼(t_p−t)^ψ, where t_p is the pinning time in the finite system involved.     

Magnetoresistance due to domain wall bulging

The effect of bulging of domain wall (DW) on the magnetoresistance (MR) is investigated. With taking into account the auto-correlation between the points of the interface, one can formulate the mobility within the relaxation time approximation scheme. The results show that the bulging of DW, evaluated with the commonly accepted magnetic parameters for typical ferromagnetic materials of Co, Fe and Ni, has a countable role into the MR.     

Magnetoresistance in a constricted domain wall

We show that a thin Gd layer inserted between two thicker layers of permalloy contains an in-plane domain wall whose width can be controlled by varying the thickness of the Gd layer. The magnetoresistance of this structure has been measured with the current perpendicular to the plane, thus eliminating spurious contributions which have complicated previous measurements. This is the first measurement to show unambiguously that the domain wall contributes an additional resistance whose magnitude is in good agreement with theory.     

Discrete versus continuous antiferromagnetic domain wall

Some specific features of the domain-wall (DW) solution for an antiferromagnetic chain of classical spins are discussed. It is shown that the Peierls-Nabarro barrier is absent. However, there is a specific spin barrier (i.e. the total spin of the chain depends on the position of the centre of the wall). The value of this barrier is calculated analytically. Existence of the spin barrier leads to the conclusion that the DW is unmovable for a discrete AFM chain, in contrast to the continuous case. The energy barrier is restored in the presence of an external magnetic field.     

Static domain wall in braneworld gravity

Thermal radiation of electrically charged fermions from a rotating black hole with electric and magnetic charges in de Sitter space is considered. The tunneling probabilities for outgoing and incoming particles are obtained and the Hawking temperature is calculated. The relation for the classical action for the particles in the black hole’s background is also found.     

Lattice-scale domain wall dynamics in ferroelectrics

Ferroelectric domain walls are atomically thin, and consequently their dynamics are sensitive to the periodic potential of the underlying lattice. Despite their central role in domain dynamics, lattice-scale effects have never been directly observed. We investigate local domain dynamics in thin film ferroelectrics using atomic-force microscopy. Upon combined dc and ac electric driving, fluctuations in the local piezoresponse are observed. Fourier analysis of the fluctuations reveals the presence of narrow band and broad band noise, and Barkhausen jumps. The narrow band noise is attributed to dynamics associated with lattice-scale pinning and is reproduced by a simple physical model.     

Magnetoresistance in magnetic domain wall systems

The contribution to the magnetoresistance (MR) was calculated for a single magnetic domain wall present in a small 2D impure ferromagnetic wire. On assuming low-temperatures and spin-independent impurity scattering the mechanism responsible for a positive contribution to MR is quantum interference. It is found that the contribution increases with impurity concentration and reduces with the width of the wall. The influence on the MR of a homogeneous electric field is proved to be spin-dependent.     

Magnetic field control of 90°, 180°, and 360° domain wall resistance

In the present work, we have compared the resistance of the 90°, 180°, and 360° domain walls in the presence of external magnetic field. The calculations are based on the Boltzmann transport equation within the relaxation time approximation. One-dimensional Néel-type domain walls between two domains whose magnetization differs by angle of 90°, 180°, and 360° are considered. The results indicate that the resistance of the 360° DW is more considerable than that of the 90° and 180° DWs. It is also found that the domain wall resistance can be controlled by applying transverse magnetic field. Increasing the strength of the external magnetic field enhances the domain wall resistance. In providing spintronic devices based on magnetic nanomaterials, considering and controlling the effect of domain wall on resistivity are essential.