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B. L. Gallagher - One of the best experts on this subject based on the ideXlab platform.

  • Spin flop and crystalline Anisotropic Magnetoresistance in CuMnAs
    Physical Review B, 2020
    Co-Authors: M. Wang, R. P. Campion, K. W. Edmonds, C. Andrews, Sonka Reimers, O. J. Amin, Peter Wadley, S. F. Poole, J. Felton, B. L. Gallagher
    Abstract:

    Recent research works have shown that the magnetic order in some antiferromagnetic materials can be manipulated and detected electrically, due to two physical mechanisms: Neel-order spin-orbit torques and Anisotropic Magnetoresistance. While these observations open up opportunities to use antiferromagnets for magnetic memory devices, different physical characterization methods are required for a better understanding of those mechanisms. Here we report a magnetic field induced rotation of the antiferromagnetic Neel vector in epitaxial tetragonal CuMnAs thin films. Using soft x-ray magnetic linear dichroism spectroscopy, x-ray photoemission electron microscopy, integral magnetometry and magneto-transport methods, we demonstrate spin-flop switching and continuous spin reorientation in antiferromagnetic films with uniaxial and biaxial magnetic anisotropies, respectively. From field-dependent measurements of the magnetization and Magnetoresistance, we obtain key material parameters including the Anisotropic Magnetoresistance coefficients, magnetocrystalline anisotropy, spin-flop and exchange fields.

  • Spin flop and crystalline Anisotropic Magnetoresistance in CuMnAs
    Physical Review B, 2020
    Co-Authors: M. Wang, R. P. Campion, K. W. Edmonds, C. Andrews, Sonka Reimers, O. J. Amin, Peter Wadley, S. F. Poole, J. Felton, B. L. Gallagher
    Abstract:

    We report magnetic-field-induced rotation of the antiferromagnetic N\'eel vector in epitaxial CuMnAs thin films. First, using soft x-ray magnetic linear dichroism spectroscopy as well as magnetometry, we demonstrate spin-flop switching and continuous spin reorientation in films with uniaxial and biaxial magnetic anisotropies, respectively, for applied magnetic fields of the order of 2 T. The remnant antiferromagnetic domain configurations are determined using x-ray photoemission electron microscopy. Next, we show that the N\'eel vector reorientations are manifested in the longitudinal and transverse Anisotropic Magnetoresistance. Dependencies of the electrical resistance on the orientation of the N\'eel vector with respect to both the electrical current direction and the crystal symmetry are identified, including a weak fourth-order term evident at high magnetic fields. The results provide characterization of key parameters including the Anisotropic Magnetoresistance coefficients, magnetocrystalline anisotropy, and spin-flop field in epitaxial films of tetragonal CuMnAs, a candidate material for antiferromagnetic spintronics.

  • Interfacial contribution to thickness dependent in-plane Anisotropic Magnetoresistance
    AIP Advances, 2015
    Co-Authors: M. Tokaç, Del Atkinson, M. Wang, B. L. Gallagher, A. W. Rushforth, Shashank Jaiswal, A. T. Hindmarch
    Abstract:

    We have studied in-plane Anisotropic Magnetoresistance (AMR) in cobalt films with overlayers having designed electrically interface transparency. With an electrically opaque cobalt/overlayer interface, the AMR ratio is shown to vary in inverse proportion to the cobalt film thickness; an indication that in-plane AMR is a consequence of Anisotropic scattering with both volume and interfacial contributions. The interface scattering anisotropy opposes the volume scattering contribution, causing the AMR ratio to diminish as the cobalt film thickness is reduced. An intrinsic interface effect explains the significantly reduced AMR ratio in ultra-thin films.

  • Huge tunnelling Anisotropic Magnetoresistance in (Ga,Mn)As nanoconstrictions
    New Journal of Physics, 2008
    Co-Authors: A. D. Giddings, Tomas Jungwirth, M. N. Khalid, Shazia Yasin, R. P. Campion, K. W. Edmonds, Joerg Wunderlich, Oleg Makarovsky, David A. Williams, B. L. Gallagher
    Abstract:

    We report here large Anisotropic Magnetoresistance (AMR) behaviours in single lateral (Ga,Mn)As nanoconstrictions of up to 1300%, along with large multistable telegraphic switching. The nanoconstriction devices are fabricated using high-resolution electron beam lithography of a 5?nm thick (Ga,Mn)As epilayer. The unusual behaviour exhibited by these devices is discussed in the context of existing theories for enhanced AMR ferromagnetic semiconductor nanoscale devices, particularly with regard to the dependence on the magnetotransport of the bulk material. We conclude that our results are most consistent with the Coulomb blockade AMR mechanism.

Wulf Wulfhekel - One of the best experts on this subject based on the ideXlab platform.

  • Large tunneling Anisotropic Magnetoresistance mediated by surface states
    Physical Review B, 2018
    Co-Authors: Marie Hervé, Timofey Balashov, Arthur Ernst, Wulf Wulfhekel
    Abstract:

    We investigated the tunneling Anisotropic Magnetoresistance (TAMR) in thick hcp Co films at cryogenic temperatures using scanning tunneling microscopy. At around -350 mV, a strong TAMR up to 30\% is found with a characteristic voltage dependence and a reversal of sign. With the help of \textit{ab initio} calculations the TAMR can be traced back to a spin-polarized occupied surface states that experience a strong spin-orbit interaction leading to a magnetization direction depending hybridization with bulk states.

  • Large tunneling Anisotropic Magnetoresistance mediated by surface states
    Physical Review B, 2018
    Co-Authors: Marie Hervé, Timofey Balashov, Arthur Ernst, Wulf Wulfhekel
    Abstract:

    The tunneling Anisotropic Magnetoresistance (TAMR) effect, which is caused by a change in the tunneling density of state of a magnetic layer with change of magnetization direction, has great potential in application in magnetic data storage devices as it only requires one of the electrodes of a tunneling junction to be magnetic. Unfortunately, experimental TAMR values are currently limited to about 10%, requiring improvement for practical use. Here, the authors show that the TAMR in hcp Co can be boosted to 30% by magnetization-dependent hybridization of surface and bulk states. This effect is a general property of hcp Co and can be used in structures suitable for applications.

Laurens W. Molenkamp - One of the best experts on this subject based on the ideXlab platform.

  • Tunneling Anisotropic Magnetoresistance in organic spin valves
    Physical Review B, 2011
    Co-Authors: M. Grünewald, Charles Gould, M. Wahler, F. Schumann, M. Michelfeit, Ralf Schmidt, Frank Würthner, Georg Schmidt, Laurens W. Molenkamp
    Abstract:

    We report the observation of tunneling Anisotropic Magnetoresistance (TAMR) in an organic spin-valve-like structure with only one ferromagnetic electrode. The device is based on a new high mobility perylene diimide-based n-type organic semiconductor. The effect originates from the tunneling injection from the LSMO contact and can thus occur even for organic layers which are too thick to support the assumption of tunneling through the layer. Magnetoresistance measurements show a clear spin-valve signal, with the typical two step switching pattern caused by the magnetocrystalline anisotropy of the epitaxial magnetic electrode.

  • Tunneling Anisotropic Magnetoresistance-Based Devices
    IEEE Transactions on Electron Devices, 2007
    Co-Authors: C. Gould, Georg Schmidt, Laurens W. Molenkamp
    Abstract:

    The paper demonstrates the operation of several devices based on tunneling Anisotropic Magnetoresistance. This effect, which originates from the interplay between the magnetic and transport properties in magnetic materials with strong spin-orbit coupling such as the ferromagnetic semiconductor (Ga,Mn)As, leads to a dependence of the tunneling resistance of devices with respect to the direction of the magnetization in the (Ga,Mn)As layer. We show that such devices can be operated as either information storage elements or sensors. It was also demonstrated that they can be used in either volatile or nonvolatile mode and that they provide either two-state or multiple state devices in either of these modes. Lastly, we present experimental evidence that they can be coupled to traditional ferromagnetic materials to still further enhance the variety of possible device functionalities

  • Tunnelling Anisotropic Magnetoresistance (TAMR)
    INTERMAG 2006 - IEEE International Magnetics Conference, 2006
    Co-Authors: Charles Gould, C. Ruester, G. Schmidt, Laurens W. Molenkamp
    Abstract:

    This paper reports on the the discovery of a novel Magnetoresistance called tunnelling Anisotropic Magnetoresistance (TAMR), which may be harnessed for device applications as both volatile and non-volatile memory. TAMR arises when tunnelling into a material with large spin orbit coupling and magnetic anisotropy such as the ferromagnetic semiconductor (Ga,Mn)As. It results from the strong coupling between the holes and the Mn system, which translates the magnetic anisotropy into an anisotropy in the transport density of states (DOS). This effect was first observed in a Au/AlOx/(Ga,Mn)As tunnel structure.

Stefan Heinze - One of the best experts on this subject based on the ideXlab platform.

  • Ballistic Anisotropic Magnetoresistance of Single-Atom Contacts.
    Nano Letters, 2016
    Co-Authors: Johannes Schöneberg, F. Otte, Yuriy Mokrousov, Nicolas Néel, Alexander Weismann, Jörg Kröger, Richard Berndt, Stefan Heinze
    Abstract:

    Anisotropic Magnetoresistance, that is, the sensitivity of the electrical resistance of magnetic materials on the magnetization direction, is expected to be strongly enhanced in ballistic transport through nanoscale junctions. However, unambiguous experimental evidence of this effect is difficult to achieve. We utilize single-atom junctions to measure this ballistic Anisotropic Magnetoresistance (AMR). Single Co and Ir atoms are deposited on domains and domain walls of ferromagnetic Fe layers on W(110) to control their magnetization directions. They are contacted with nonmagnetic tips in a low-temperature scanning tunneling microscope to measure the junction conductances. Large changes of the Magnetoresistance occur from the tunneling to the ballistic regime due to the competition of localized and delocalized d-orbitals, which are differently affected by spin–orbit coupling. This work shows that engineering the AMR at the single atom level is feasible.

  • Molecular Anisotropic Magnetoresistance
    Physical Review B, 2015
    Co-Authors: F. Otte, Stefan Heinze, Yuriy Mokrousov
    Abstract:

    Using density functional theory calculations, we demonstrate that the effect of Anisotropic Magnetoresistance (AMR) can be enhanced by orders of magnitude with respect to conventional bulk ferromagnets in junctions containing molecules sandwiched between ferromagnetic leads. We study ballistic transport in metal-benzene complexes contacted by 3d transition-metal wires. We show that a gigantic AMR can arise from spin-orbit coupling effects in the leads, drastically enhanced by orbital-symmetry filtering properties of the molecules. We further discuss how this molecular Anisotropic Magnetoresistance (MAMR) can be tuned by the proper choice of materials and their electronic properties.

  • Tunneling Anisotropic Magnetoresistance at the single-atom limit.
    Physical Review Letters, 2013
    Co-Authors: Nicolas Néel, Jörg Kröger, Richard Berndt, S. Schröder, P. Ferriani, N. Ruppelt, Stefan Heinze
    Abstract:

    The tunneling Anisotropic Magnetoresistance (TAMR) of single Co atoms adsorbed on a double-layer Fe film on W(110) is observed by scanning tunneling spectroscopy. Without applying an external magnetic field the TAMR is found by comparing spectra of atoms that are adsorbed on the domains and domain walls of the Fe film. The TAMR can be as large as 12% and repeatedly changes sign as a function of bias voltage. First-principles calculations show that the hybridization between Co d states of different orbital symmetries depends on the magnetization direction via spin-orbit coupling. This leads to an anisotropy of the density of states and thus induces a TAMR.

  • Tunneling Anisotropic Magnetoresistance on the atomic scale
    Physical Review B, 2012
    Co-Authors: K. Von Bergmann, Matthias Menzel, David Serrate, Yasuo Yoshida, S. Schröder, P. Ferriani, André Kubetzka, Roland Wiesendanger, Stefan Heinze
    Abstract:

    We demonstrate the occurrence of tunneling Anisotropic Magnetoresistance on the atomic scale using scanning tunneling microscopy (STM). Our experiments show that noncollinear atomic-scale magnetic structures can be revealed in STM using nonmagnetic tips. These observations can be explained by a variation of the local density of states of an atom depending on its magnetization direction due to spin-orbit interaction. STM simulations based on this effect are in excellent agreement with the experimental images and can explain the bias-voltage-dependent contrast found for two-dimensionally modulated spin textures.

Steven S.-l. Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Anisotropic Magnetoresistance driven by surface spin orbit scattering
    Physical Review B, 2015
    Co-Authors: Steven S.-l. Zhang, Giovanni Vignale, Shufeng Zhang
    Abstract:

    In a bilayer consisting of an insulator (I) and a ferromagnetic metal (FM), interfacial spin orbit scattering leads to spin mixing of the two conducting channels of the FM, which results in an unconventional Anisotropic Magnetoresistance (AMR). We theoretically investigate the magnetotransport in such bilayer structures by solving the spinor Boltzmann transport equation with generalized Fuchs-Sondheimer boundary condition that takes into account the effect of spin orbit scattering at the interface. We find that the new AMR exhibits a peculiar angular dependence which can serve as a genuine experimental signature. We also determine the dependence of the AMR on film thickness as well as spin polarization of the FM.

  • Angular dependence of Anisotropic Magnetoresistance in magnetic systems
    Journal of Applied Physics, 2014
    Co-Authors: Steven S.-l. Zhang, Shufeng Zhang
    Abstract:

    Anisotropic Magnetoresistance (AMR), whose physical origin is attributed to the combination of spin dependent scattering and spin orbital coupling (SOC), usually displays simple angular dependence for polycrystalline ferromagnetic metals. By including generic spin dependent scattering and spin Hall (SH) terms in the Ohm's law, we explicitly show that various magneto-transport phenomena such as anomalous Hall (AH), SH, planar Hall (PH) and AMR could be quantitatively related for bulk polycrystalline ferromagnetic metals. We also discuss how AMR angular dependence is affected by the presence of interfacial SOC in magnetic layered structure.