1,662 research outputs found
Minimal field requirement in precessional magnetization switching
We investigate the minimal field strength in precessional magnetization
switching using the Landau-Lifshitz-Gilbert equation in under-critically damped
systems. It is shown that precessional switching occurs when localized
trajectories in phase space become unlocalized upon application of field
pulses. By studying the evolution of the phase space, we obtain the analytical
expression of the critical switching field in the limit of small damping for a
magnetic object with biaxial anisotropy. We also calculate the switching times
for the zero damping situation. We show that applying field along the medium
axis is good for both small field and fast switching times.Comment: 6 pages, 7 figure
Anisotropic magnetoresistance in antiferromagnetic Sr2IrO4
We report point-contact measurements of anisotropic magnetoresistance (AMR)
in a single crystal of antiferromagnetic (AFM) Mott insulator Sr2IrO4. The
point-contact technique is used here as a local probe of magnetotransport
properties on the nanoscale. The measurements at liquid nitrogen temperature
revealed negative magnetoresistances (MRs) (up to 28%) for modest magnetic
fields (250 mT) applied within the IrO2 a-b plane and electric currents flowing
perpendicular to the plane. The angular dependence of MR shows a crossover from
four-fold to two-fold symmetry in response to an increasing magnetic field with
angular variations in resistance from 1-14%. We tentatively attribute the
four-fold symmetry to the crystalline component of AMR and the field-induced
transition to the effects of applied field on the canting of AFM-coupled
moments in Sr2IrO4. The observed AMR is very large compared to the crystalline
AMRs in 3d transition metal alloys/oxides (0.1-0.5%) and can be associated with
the large spin-orbit interactions in this 5d oxide while the transition
provides evidence of correlations between electronic transport, magnetic order
and orbital states. The finding of this work opens an entirely new avenue to
not only gain a new insight into physics associated with spin-orbit coupling
but also better harness the power of spintronics in a more technically
favorable fashion.Comment: 13 pages, 3 figure
Magnetic relaxation in metallic films: Single and multilayer structures
The intrinsic magnetic relaxations in metallic films will be discussed. It will be shown that the intrinsic damping mechanism in metals is
caused by incoherent scattering of itinerant electron-hole pair
excitations by phonons and magnons. Berger [L. Berger, Phys. Rev. B
54, 9353 (1996)] showed that the interaction between spin waves and
itinerant electrons in multilayers can lead to interface Gilbert
damping. Ferromagnetic resonance (FMR) studies were carried out using
magnetic single and double layer films. The FMR linewidth of the Fe
films in the double layer structures was found to always be larger than
the FMR linewidth measured for the single Fe films having the same
thickness. The increase in the FMR linewidth scaled inversely with the
film thickness, and was found to be linearly dependent on the microwave
frequency. These results are in agreement with Berger's predictions.
(C) 2002 American Institute of Physics
Spin separation in cyclotron motion
Charged carriers with different spin states are spatially separated in a
two-dimensional hole gas. Due to strong spin-orbit interaction holes at the
Fermi energy have different momenta for two possible spin states travelling in
the same direction and, correspondingly, different cyclotron orbits in a weak
magnetic field. Two point contacts, acting as a monochromatic source of
ballistic holes and a narrow detector in the magnetic focusing geometry are
demonstrated to work as a tunable spin filter.Comment: 4 pages, 2 figure
Anisotropic Magnetoresistance in Antiferromagnetic Sr\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e
We report point-contact measurements of anisotropic magnetoresistance (AMR) in a single crystal of antiferromagnetic Mott insulator Sr2IrO4. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature reveal negative magnetoresistances (up to 28%) for modest magnetic fields (250 mT) applied within the IrO2 a−b plane and electric currents flowing perpendicular to the plane. The angular dependence of magnetoresistance shows a crossover from fourfold to twofold symmetry in response to an increasing magnetic field with angular variations in resistance from 1% to 14%. We tentatively attribute the fourfold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of antiferromagnetic-coupled moments in Sr2IrO4. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys or oxides (0.1%–0.5%) and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order, and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also to better harness the power of spintronics in a more technically favorable fashion
Electrically Tunable Transport in the Antiferromagnetic Mott Insulator Sr\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e
Electronic transport properties of the antiferromagnetic Mott insulator Sr2IrO4 have been investigated under extremely high electric biases. Using nanoscale contacts, we apply electric fields up to a few MV/m to a single crystal of Sr2IrO4 and observe a continuous reduction in the material\u27s resistivity with increasing bias, characterized by a reduction in the transport activation energy by as much as 16%. Temperature-dependent resistivity measurements provide a means to unambiguously retrieve the bias dependence of the activation energy from the Arrhenius plots at different biases. We further demonstrate the feasibility of reversible resistive switching induced by the electric bias, which is of interest for the emerging field of antiferromagnetic spintronics. Our findings demonstrate the potential of electrical means for tuning electronic properties in 5d transition-metal oxides and suggest a promising path towards development of next-generation functional devices
Temperature Dependence of Anisotropic Magnetoresistance in Antiferromagnetic Sr\u3csub\u3e2\u3c/sub\u3eIrO\u3csub\u3e4\u3c/sub\u3e
Temperature-dependent magnetotransport properties of the antiferromagnetic semiconductor Sr2IrO4 are investigated with point-contact devices. The point-contact technique allows to probe very small volumes and, therefore, to look for electronic transport on a microscopic scale. Point-contact measurements with single crystals of Sr2IrO4 were intended to see whether the additional local resistance associated with a small contact area between a sharpened Cu tip and the antiferromagnet shows magnetoresistance (MR) such as that seen in bulk crystals. Point-contact measurements at liquid nitrogen temperature revealed large MRs (up to 28%) for modest magnetic fields (250 mT) applied within an IrO2 (ab) plane with angular dependence showing a crossover from four-fold to two-fold symmetry with an increasing magnetic field. Point contact measurement exhibits distinctive anisotropic magnetoresistance (AMR) in comparison to a bulk experiment, imposing intriguing questions about the mechanism of AMR in this material. Temperature-dependent MR measurements show that the MR falls to zero at the Neel temperature, but the temperature dependence of the MR ratio differs qualitatively from that of the resistivity. This AMR study helps to unveil the entanglement between electronic transport and magnetism in Sr2IrO4 while the observed magnetoresistive phenomena can be potentially used to sense the antiferromagnetic order parameter in spintronic applications
Electrically Tunable Band Gap in Antiferromagnetic Mott Insulator Sr2IrO4
The electronic band gap in conventional semiconductor materials, such as
silicon, is fixed by the material's crystal structure and chemical composition.
The gap defines the material's transport and optical properties and is of great
importance for performance of semiconductor devices like diodes, transistors
and lasers. The ability to tune its value would allow enhanced functionality
and flexibility of future electronic and optical devices. Recently, an
electrically tunable band gap was realized in a 2D material - electronically
gated bilayer graphene [1-3]. Here we demonstrate the realization of an
electrically tunable band gap in a 3D antiferromagnetic Mott insulator Sr2IrO4.
Using nano-scale contacts between a sharpened Cu tip and a single crystal of
Sr2IrO4, we apply a variable external electric field up to a few MV/m and
demonstrate a continuous reduction in the band gap of Sr2IrO4 by as much as
16%. We further demonstrate the feasibility of reversible resistive switching
and electrically tunable anisotropic magnetoresistance,which provide evidence
of correlations between electronic transport, magnetic order, and orbital
states in this 5d oxide. Our findings suggest a promising path towards band gap
engineering in 5d transition-metal oxides that could potentially lead to
appealing technical solutions for next-generation electronic devices.Comment: 14 pages, 6 figure
Current-Driven Magnetization Dynamics in Magnetic Multilayers
We develop a quantum analog of the classical spin-torque model for
current-driven magnetic dynamics. The current-driven magnetic excitation at
finite field becomes significantly incoherent. This excitation is described by
an effective magnetic temperature rather than a coherent precession as in the
spin-torque model. However, both the spin-torque and effective temperature
approximations give qualitatively similar switching diagrams in the
current-field coordinates, showing the need for detailed experiments to
establish the proper physical model for current-driven dynamics.Comment: 5 pages, 2 figure
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