Massive Skyrmions in quantum Hall ferromagnets

Abolfath, M.; Mullen, Kieran; Stoof, H. T. C.

doi:10.1103/physrevb.63.075315

Cited by 69 publications

(140 citation statements)

References 25 publications

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“…We fixed the volume density of holes such that E F (γ 2 = 2.1, h 0 = 0) = 1. Experimentally [17,21], E F (h 0 )/h 0 ∼ 1 which corresponds to h 0 ∼ 1.5. The convergence of the numerical scheme is verified by checking the unitarity of the scattering matrix.…”

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confidence: 99%

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Intrinsic Domain-Wall Resistance in Ferromagnetic Semiconductors

Nguyen¹,

Shchelushkin²,

Brataas³

2006

Phys. Rev. Lett.

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Transport through zincblende magnetic semiconductors with magnetic domain walls is studied theoretically. We show that these magnetic domain walls have an intrinsic resistance due to the effective hole spin-orbit interaction. The intrinsic resistance is independent of the domain wall shape and width, and survives the adiabatic limit. For typical parameters, the intrinsic domain wall resistance is comparable to the Sharvin resistance and should be experimentally measurable.Understanding magnetic topological defects is crucial in developing devices that utilize the electron spin. Domain walls are topological defects between homogeneous magnetic domains. The domain wall dynamics has traditionally been induced by external magnetic fields. There has recently been a large interest in the scientific community on current induced magnetization dynamics, where domain walls and domains change in response to applied electric currents [1]. Domain walls can also be electrically detected, by their electrical resistance. Knowledge of the domain wall's effect on the electrical resistance is important for the understanding of spin transport in condensed matter and for the electrical detection of magnetic topological defects.Transport through domain walls have been extensively studied in metallic systems, theoretically [2] and experimentally [3]. The domain wall resistance is defined as R w = R − R 0 , where R and R 0 are resistances with a domain wall and with homogeneous magnetization, respectively. When the domain wall is thinner than the mean free path, in the ballistic regime, R w is positive. In diffusive systems, when the domain wall is wider than the mean free path, the sign of the domain wall resistance is still under debate, i.e. the domain wall can increase or decrease the resistance of the ferromagnet. In ballistic and diffusive metal systems, R w approaches zero with increasing domain wall width and vanishes in the adiabatic limit when the domain wall is much wider than the Fermi wavelength.Ferromagnetic semiconductors integrate magnetization controlled spin transport with gate controlled carrier densities in semiconductors. Domain walls in these systems have been recently studied experimentally [4,5,6,7]. The strong interaction between the spin of the effective holes and their orbits in dilute magnetic semiconductors changes the transport properties of magnetic domain walls qualitatively. In this Letter, we show that domain walls in zincblende magnetic semiconductors have an intrinsic resistance R I w which is the part of R w that survives the adiabatic limit. R I w is independent of the width and detailed shape of the domain walls and is due to the effective spin-orbit interaction.Related manifestations of the coupling between the spin-orbit interactions and the magnetizations are the anisotropic magneto resistance (AMR) [8,9,10,11] and the tunneling anisotropic magneto resistance (TAMR) [4,13,14]. In domain walls, some carriers are prevented by the spin-orbit interaction to adiabatically adapt to the change in the ...

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“…A six band version of Eq. 1 explains many features of zincblende magnetic semiconductors [16,17,18]. We employ the spherical approximation [19] and disregard two split-off bands.…”

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Intrinsic Domain-Wall Resistance in Ferromagnetic Semiconductors

Nguyen¹,

Shchelushkin²,

Brataas³

2006

Phys. Rev. Lett.

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“…We have performed microscopic calculations to estimate chemical potential anisotropies in (Ga, Mn)As epilayers. We use the effective kinetic-exchange model that has been frequently employed to study these dilute magnetic moment p-type semiconductors, particularly the properties related to the strong spin-orbit coupling in the valence band [8][9][10][11][12][13]. The zero-temperature calculations assume cubic magneto-crystalline anisotropy associated with the zinc-blende crystal structure plus an additional uniaxial field (as observed experimentally) modeled [19] by introducing a weak in-plane shear strain e xy ¼ 0.001.…”

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confidence: 99%

“…Our SETs are fabricated from p-type (Ga,Mn)As, a ferromagnetic semiconductor for which parameters derived from the spin-orbit coupled band structure are known to be strongly anisotropic with respect to the magnetization orientation [8][9][10][11][12][13][14]. A schematic diagram of the device are shown in Fig.…”

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confidence: 99%

Coulomb blockade anisotropic magnetoresistance and voltage controlled magnetic switching in a ferromagnetic GaMnAs single electron transistor

Wunderlich

Jungwirth

Irvine

et al. 2007

Journal of Magnetism and Magnetic Materials

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“…Ferromagnetism is originated by the exchange interaction between the spin of the localized Mn and the itinerant holes. In the case of metallic samples the mean field and virtual crystal (MF-VC) approximation 13,14,15,16 accounts for a number of experimental facts like the dependence of T c on both the Mn and hole densities 13 , the magnetic anisotropy 14 and magnetic circular dichroism 13 . In this approach spontaneous magnetization is characterized by effective Zeeman magnetic field H which represents the effect of exchange interaction of the Mn magnetization on the spin of the holes.…”

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Tunnel magnetoresistance in GaMnAs: Going beyond Jullière formula

Brey

Tejedor

Fernández-Rossier

2004

Applied Physics Letters

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The relation between tunnel magneto-resistance (TMR) and spin polarization is explored for GaMnAs/GaAlAs/GaMnAs structures where the carriers experience strong spin-orbit interactions. TMR is calculated using Landauer approach. The materials are described in the 6 band k · p model which includes spin orbit interaction. Ferromagnetism is described in the virtual crystal mean field approximations. Our results indicate that TMR is a function of of spin polarization and barrier thickness. As a result of the stong spin orbit interactions, TMR also depends on the the angle between current flow direction and the electrode magnetization. These results compromise the validity of Julliere formula. PACS numbers:The relative orientation of the magnetization of two ferromagnetic electrodes can affect dramatically electron transport across a tunnelling barrier connecting them. This phenomenon gives rise to the so called tunnelmagneto-resistance 1 (TMR), TMR = (R AP − R P )/R AP where R AP and R P are the resistances for anti-parallel and parallel orientations respectively. TMR is exploited to fabricate devices which are ultra-sensitive to variations of an external magnetic field 2 . Microscopic understanding of TMR, based upon the hypothesis that spin is conserved in the tunnelling process, leads to the well known Julliere Formula 3,4 :which relates TMR with P L,R , the polarizations of the left (L) and right (R) electrodes. Assuming Eq. (1) is correct, it permits to extract the spin polarization of the electrodes from the value of TMR in symmetric tunnel junctions, regardless of the physical properties of the barrier. Eq. (1) can be derived doing second order perturbation theory in tunnelling amplitude 5 . Diluted magnetic semiconductors like Ga 1−x Mn x As are ferromagnetic below T C ≃ 150 K 6 . This type of materials rise a lot of interest because they afford the integration of ferromagnetic and semiconducting functionalities in a single device 7,8 . Substitutional impurities of Mn in GaAs are acceptors. The holes released by the Mn are responsible of the magnetic ordering and transport properties of Ga 1−x Mn x As. Several groups have been able to fabricate tunnel junctions * brey@icmm.csic.es with GaMnAs in the electrodes 9,10,11 and they have reported large values of TMR finding that its value depends on the properties of the barrier 9 . Furthermore, spin orbit (SO) interactions for the holes in the valence band of GaAs is very strong (∆ SO ≃ 0.34 eV) so that the spin of the holes is not a good quantum number. Both the experimental results 9,10,11 and the failure of Julliere's hypothesis on spin conservation, lead us to study TMR in GaMnAs/AlAs/GaMnAs systems using a nonpertubative approach which fully includes spin orbit interactions. We anticipate our main result: in GaMnAs based heterostructures TMR depends on both the barrier thickness, d b , the angle formed by the current flow and the magnetization. All these features depend on the strength of the SO coupling and are relevant for the use of GaMnAs based heterostru...

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Massive Skyrmions in quantum Hall ferromagnets

Cited by 69 publications

References 25 publications

Intrinsic Domain-Wall Resistance in Ferromagnetic Semiconductors

Intrinsic Domain-Wall Resistance in Ferromagnetic Semiconductors

Coulomb blockade anisotropic magnetoresistance and voltage controlled magnetic switching in a ferromagnetic GaMnAs single electron transistor

Tunnel magnetoresistance in GaMnAs: Going beyond Jullière formula

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