Permalloy-based carbon nanotube spin-valve

Aurich, H.; Baumgärtner, A.; Freitag, F.; Eichler, Alexander; Trbovic, Jelena; Schönenberger, Christian

doi:10.1063/1.3502600

Cited by 49 publications

(60 citation statements)

References 15 publications

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“…The magnetic field at the NW position is a superposition of the external field and the FSG stray field. The switching field is the same in all experiments on this device and coincides with the FSG magnetization inversion expected from the designed Py strips [6,7]. Since the external field is aligned with the FSGs, we assume that on average the stray field points in the same direction and thus adds an offset field, B tot = B + B st .…”

Section: Single Dot Mr and Mrsmentioning

confidence: 99%

“…For nonmagnetic bulk materials, one typically finds a parabolic field dependence and a saturation, but it can also be linear to large magnetic fields, either due to disorder [1], or due to a linear dispersion relation [2], for example on the surface of a topological insulator [3]. Many MR effects and applications are known for magnetic materials [4,5], for example the anisotropic magnetoresistance (AMR) used to characterize magnetic contacts [6,7], or the tunneling magnetoresistance (TMR), in which electrons tunnel between two magnetic reservoirs, resulting in a resistance that depends on the relative orientation of the reservoir magnetizations. TMR typically shows hysteretic rectangular MR loops in up and down sweeps of B.…”

Section: Introductionmentioning

confidence: 99%

“…The split gate consists of a pair of long, narrow ferromagnetic Permalloy (Py) strips which we call ferromagnetic sidegates (FSGs). The strips have a single domain magnetization with a switching field determined by the geometric width [6,7]. In addition, these FSGs can be used individually as electrical gates.…”

Section: Introductionmentioning

confidence: 99%

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Magnetoresistance engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates

et al. 2016

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We present magnetoresistance (MR) experiments on an InAs nanowire quantum dot device with two ferromagnetic sidegates (FSGs) in a split-gate geometry. The wire segment can be electrically tuned to a single dot or to a double dot regime using the FSGs and a backgate. In both regimes we find a strong MR and a sharp MR switching of up to 25% at the field at which the magnetizations of the FSGs are inverted by the external field. The sign and amplitude of the MR and the MR switching can both be tuned electrically by the FSGs. In a double dot regime close to pinch-off we find two sharp transitions in the conductance, reminiscent of tunneling MR (TMR) between two ferromagnetic contacts, with one transition near zero and one at the FSG switching fields. These surprisingly rich characteristics we explain in several simple resonant tunneling models. For example, the TMR-like MR can be understood as a stray-field controlled transitions between singlet and triplet double dot states. Such local magnetic fields are the key elements in various proposals to engineer novel states of matter and may be used for testing electron spin based Bell inequalities.

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Section: Single Dot Mr and Mrsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Magnetoresistance engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates

et al. 2016

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“…Py usually refers to Ni 1Àx Fe x alloys that have a vanishingly small magnetocrystalline anisotropy and magnetostriction but extremely large magnetic permeability. These unique properties make Py one of the most important soft magnets for a variety of applications, such as free layers in spin-valve magnetic-reading heads [2,3]. The Py/MgO combination has been widely used in magnetic tunnel junctions (MTJs) devices.…”

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confidence: 99%

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100)

Rao

Prater

et al. 2014

Current Opinion in Solid State and Materials Science

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a b s t r a c tIn magnetic random access memory (MRAM) devices, soft magnetic thin film elements such as permalloy (Py) are used as unit cells of information. The epitaxial integration of these elements with the technologically important substrate Si (1 0 0) and a thorough understanding of their magnetic properties are critical for CMOS-based magnetic devices. We report on the epitaxial growth of Ni 82.5 Fe 17.5 (permalloy, Py) on Si (1 0 0) using a TiN/MgO buffer layer. Initial stages of growth are characterized by the formation of discrete islands that gradually merge into a continuous film as deposition times are extended. Interestingly, we find that the magnetic features of Py films in early stages of island coalescence are distinctly different from the films formed initially (discrete islands) and after extended deposition times (narrow distribution of equiaxed granular films). Isothermal in-plane and out-of-plane magnetic measurements performed on these transitional films show highly anisotropic magnetic behavior with an easy magnetization axis lying in the plane of the film. Importantly, when this sample is zero-field cooled, a positive exchange bias and vertical loop shift are observed, unusual for a soft ferromagnet like Py. Repeated field cycling and hysteresis loops up to the fields of 7T produced reproducible hysteresis loops indicating the existence of strongly pinned spin configurations. Classical interface related exchange bias models cannot explain the observed magnetic features of the transitional Py films. We believe that the anomalous magnetic behavior of such Py films may be explained by considering the highly irregular morphology that develops at intermediate growth times that are possibly also undergoing a transition from Bloch to Neel domain wall structures as a function of Py island size. This study broadens the current understanding of magnetic properties of Py thin layers for technological applications in magneto-electronic devices, integrated with Si (1 0 0). Ó 2014 Elsevier Ltd. All rights reserved.Motivated by the proposed racetrack memory patented [1] by Parkin et al, a great deal of research activity has been devoted to Permalloy (Py) magnetic nanostructures for high frequency applications. Py usually refers to Ni 1Àx Fe x alloys that have a vanishingly small magnetocrystalline anisotropy and magnetostriction but extremely large magnetic permeability. These unique properties make Py one of the most important soft magnets for a variety of applications, such as free layers in spin-valve magnetic-reading heads [2,3]. The Py/MgO combination has been widely used in magnetic tunnel junctions (MTJs) devices. More recently, Py is being extensively used [4,5] to demonstrate electric field control of ferromagnetism (FM) in multiferroic based devices. Hence, exploring and understanding the magnetic properties of Py when interfaced with magnetic/non-magnetic oxide materials is of primary importance.To date, epitaxial Py layers have been deposited [6] on MgO bulk substrates using molecular beam...

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“…Based on the Keldysh nonequilibrium Green's function (NEGF) formalism, we formulate and derive in closed form the time-averaged STT under ac modulation. To illustrate the idea, we further analyze carbon nanotube (CNT) MTJs under ac modulation: such CNT MTJ can be well described by a tight-binding atomic model [21], and it was also realized experimentally [22]. Our calculation indicates that opening more transport channels by ac modulation at designated frequency ω enhances STT: both in-plane and out-of-plane bias-induced STTs exhibit significant enhancement by up to 12 and 75 times, respectively.…”

Section: Introductionmentioning

confidence: 99%

Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation

et al. 2017

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The phenomenon of spin transfer torque (STT) has attracted a great deal of interests due to its promising prospects in practical spintronic devices. In this paper, we report a theoretical investigation of STT in a noncollinear magnetic tunnel junction under ac modulation based on the nonequilibrium Green's function formalism, and derive a closed-formulation for predicting the time-averaged STT. Using this formulation, the ac STT of a carbon-nanotube-based magnetic tunnel junction is analyzed. Under ac modulation, the low-bias linear (quadratic) dependence of the in-plane (out-of-plane) torque on bias still holds, and the sin θ dependence on the noncollinear angle is maintained. By photon-assisted tunneling, the bias-induced components of the in-plane and out-of-plane torques can be enhanced significantly, about 12 and 75 times, respectively. Our analysis reveals the condition for achieving optimized STT enhancement and suggests that ac modulation is a very effective way for electrical manipulation of STT.

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Permalloy-based carbon nanotube spin-valve

Cited by 49 publications

References 15 publications

Magnetoresistance engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates

Magnetoresistance engineering and singlet/triplet switching in InAs nanowire quantum dots with ferromagnetic sidegates

Positive exchange bias in epitaxial permalloy/MgO integrated with Si (100)

Enhancing the spin transfer torque in magnetic tunnel junctions by ac modulation

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