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University of Nebraska - Lincoln

Department of Physics and Astronomy: Faculty Publications

Series

2015

Articles 1 - 11 of 11

Full-Text Articles in Physical Sciences and Mathematics

Spin-Fluctuation Mechanism Of Anomalous Temperature Dependence Of Magnetocrystalline Anisotropy In Itinerant Magnets, I. A. Zhuravlev, V. P. Antropov, K. D. Belashchenko Nov 2015

Spin-Fluctuation Mechanism Of Anomalous Temperature Dependence Of Magnetocrystalline Anisotropy In Itinerant Magnets, I. A. Zhuravlev, V. P. Antropov, K. D. Belashchenko

Department of Physics and Astronomy: Faculty Publications

The origins of the anomalous temperature dependence of magnetocrystalline anisotropy in (Fe1−xCox)2B alloys are elucidated using first-principles calculations within the disordered local moment model. Excellent agreement with experimental data is obtained. The anomalies are associated with the changes in band occupations due to Stoner-like band shifts and with the selective suppression of spin-orbit “hot spots” by thermal spin fluctuations. Under certain conditions, the anisotropy can increase, rather than decrease, with decreasing magnetization due to these peculiar electronic mechanisms, which contrast starkly with those assumed in existing models.

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Spin-Dependent Two-Color Kapitza-Dirac Effects, Scot Mcgregor, Wayne Cheng-Wei Huang, Herman Batelaan, Bradley Allan Shadwick Aug 2015

Spin-Dependent Two-Color Kapitza-Dirac Effects, Scot Mcgregor, Wayne Cheng-Wei Huang, Herman Batelaan, Bradley Allan Shadwick

Department of Physics and Astronomy: Faculty Publications

In this paper we present an analysis of the spin behavior of electrons propagating through a laser field. We present an experimentally realizable scenario in which spin-dependent effects of the interaction between the laser and the electrons are dominant. The laser interaction strength and incident electron velocity are in the nonrelativistic domain. This analysis may thus lead to novel methods of creating and characterizing spin-polarized nonrelativistic femtosecond electron pulses.

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Discrete Excitation Spectrum Of A Classical Harmonic Oscillator In Zero-Point Radiation, Wayne Cheng-Wei Huang, Herman Batelaan Mar 2015

Discrete Excitation Spectrum Of A Classical Harmonic Oscillator In Zero-Point Radiation, Wayne Cheng-Wei Huang, Herman Batelaan

Department of Physics and Astronomy: Faculty Publications

We report that upon excitation by a single pulse, a classical harmonic oscillator immersed in the classical electromagnetic zero-point radiation exhibits a discrete harmonic spectrum in agreement with that of its quantum counterpart. This result is interesting in view of the fact that the vacuum field is needed in the classical calculation to obtain the agreement.

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Optical Control Of Electron Phase Space In Plasma Accelerators With Incoherently Stacked Laser Pulses, Serguei Y. Kalmuykov, X Davoine, R Lehe, A F. Lifschitz, Bradley Allan Shadwick Jan 2015

Optical Control Of Electron Phase Space In Plasma Accelerators With Incoherently Stacked Laser Pulses, Serguei Y. Kalmuykov, X Davoine, R Lehe, A F. Lifschitz, Bradley Allan Shadwick

Department of Physics and Astronomy: Faculty Publications

It is demonstrated that synthesizing an ultrahigh-bandwidth, negatively chirped laser pulse by incoherently stacking pulses of different wavelengths makes it possible to optimize the process of electron self-injection in a dense, highly dispersive plasma (n0 ~ 1019 c~3). Avoiding transformation of the driving pulse into a relativistic optical shock maintains a quasi-monoenergetic electron spectrum through electron dephasing and boosts electron energy far beyond the limits suggested by existing scaling laws. In addition, evolution of the accelerating bucket in a plasma channel is shown to produce a background-free, tunable train of femtosecond-duration, 35–100 kA, time-synchronized quasi-monoenergetic electron bunches. The combination of …

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Magnetization Pumping And Dynamics In A Dzyaloshinskii-Moriya Magnet, Alexey Kovalev, Utkan Güngördü Jan 2015

Magnetization Pumping And Dynamics In A Dzyaloshinskii-Moriya Magnet, Alexey Kovalev, Utkan Güngördü

Department of Physics and Astronomy: Faculty Publications

We formulate a phenomenological description of thin ferromagnetic layers with inversion asymmetry where the single-domain magnetic dynamics experiences magnon current-induced torques and leads to magnon-motive forces. We first construct a phenomenological theory based on irreversible thermodynamics, taking into account the symmetries of the system. Furthermore, we confirm that these effects originate from Dzyaloshinskii-Moriya interactions from the analysis based on the stochastic Landau-Lifshitz-Gilbert equation. Our phenomenological results generalize to a general form of Dzyaloshinskii-Moriya interactions and to other systems, such as pyrochlore crystals and chiral magnets. Possible applications include spin current generation, magnetization reversal and magnonic cooling.

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Origin Of The Spin Reorientation Transitions In (Fe1–Xcox)2b Alloys, Kirill D. Belashchenko, Liqin Ke, Markus Dane, Lorin X. Benedict, Tej Nath Lamichhane, Valentin Taufour, Anton Jesche, Sergey L. Bud'ko, Paul C. Canfield, Vladimir P. Antropov Jan 2015

Origin Of The Spin Reorientation Transitions In (Fe1–Xcox)2b Alloys, Kirill D. Belashchenko, Liqin Ke, Markus Dane, Lorin X. Benedict, Tej Nath Lamichhane, Valentin Taufour, Anton Jesche, Sergey L. Bud'ko, Paul C. Canfield, Vladimir P. Antropov

Department of Physics and Astronomy: Faculty Publications

Low-temperature measurements of the magnetocrystalline anisotropy energy K in (Fe1–xCox)2B alloys are reported, and the origin of this anisotropy is elucidated using a first-principles electronic structure analysis. The calculated concentration dependence K(x) with a maximum near x¼0.3 and a minimum near x¼0.8 is in excellent agreement with experiment. This dependence is traced down to spin-orbital selection rules and the filling of electronic bands with increasing electronic concentration. At the optimal Co concentration, K depends strongly on the tetragonality and doubles under a modest 3% increase of the c/a ratio, suggesting that the magnetocrystalline anisotropy can be further enhanced using epitaxial …

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Strategies For Increasing The Néel Temperature Of Magnetoelectric Fe2Teo6, Sai Mu, Kirill D. Belashchenko Jan 2015

Strategies For Increasing The Néel Temperature Of Magnetoelectric Fe2Teo6, Sai Mu, Kirill D. Belashchenko

Department of Physics and Astronomy: Faculty Publications

Ways to increase the Néel temperature TN in the magnetoelectric Fe2TeO6 antiferromagnet are explored with the help of first-principles calculations. Substitution of larger ions like Zr or Hf for tellurium increases the superexchange angles. The compensating O vacancies tend to form bound complexes with Zr dopants, which do not degrade the electronic band gap. TN is estimated to increase by 15% at 12.5% Te → Zr substitution with such compensation. Substitution of N for O is favorable due to the decreased charge-transfer gap. The overall effect for N3− substitution compensated by O vacancies …

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Fast Strain Wave Induced Magnetization Changes In Long Cobalt Bars: Domain Motion Versus Coherent Rotation, S Davis, J A. Borchers, B B. Maranville, Shireen Adenwalla Jan 2015

Fast Strain Wave Induced Magnetization Changes In Long Cobalt Bars: Domain Motion Versus Coherent Rotation, S Davis, J A. Borchers, B B. Maranville, Shireen Adenwalla

Department of Physics and Astronomy: Faculty Publications

A high frequency (88 MHz) traveling strain wave on a piezoelectric substrate is shown to change the magnetization direction in 40 lm wide Co bars with an aspect ratio of 103. The rapidly alternating strain wave rotates the magnetization away from the long axis into the short axis direction, via magnetoelastic coupling. Strain-induced magnetization changes have previously been demonstrated in ferroelectric/ferromagnetic heterostructures, with excellent fidelity between the ferromagnet and the ferroelectric domains, but these experiments were limited to essentially dc frequencies. Both magneto-optical Kerr effect and polarized neutron reflectivity confirm that the traveling strain wave does rotate the magnetization away …

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Continuous Third Harmonic Generation In A Terahertz Driven Modulated Nanowire, Kathleen E. Hamilton, Alexey Kovalev, Amrit De, Leonid P. Pryadko Jan 2015

Continuous Third Harmonic Generation In A Terahertz Driven Modulated Nanowire, Kathleen E. Hamilton, Alexey Kovalev, Amrit De, Leonid P. Pryadko

Department of Physics and Astronomy: Faculty Publications

We consider the possibility of observing continuous third-harmonic generation using a strongly driven, single-band one-dimensional metal. In the absence of scattering, the quantum efficiency of frequency tripling for such a system can be as high as 93%. Combining the Floquet quasienergy spectrum with the Keldysh Green’s function technique, we derive a semiclassical master equation for a one-dimensional band of strongly and rapidly driven electrons in the presence of weak scattering by phonons. The power absorbed from the driving field is continuously dissipated by phonon modes, leading to a quasi-equilibrium in the electron distribution. We use the Kronig-Penney model with varying …

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Thresholds For Correcting Errors, Erasures, And Faulty Syndrome Measurements In Degenerate Quantum Codes, Ilya Dumer, Alexey Kovalev, Leonid P. Pryadko Jan 2015

Thresholds For Correcting Errors, Erasures, And Faulty Syndrome Measurements In Degenerate Quantum Codes, Ilya Dumer, Alexey Kovalev, Leonid P. Pryadko

Department of Physics and Astronomy: Faculty Publications

We suggest a technique for constructing lower (existence) bounds for the fault-tolerant threshold to scalable quantum computation applicable to degenerate quantum codes with sublinear distance scaling. We give explicit analytic expressions combining probabilities of erasures, depolarizing errors, and phenomenological syndrome measurement errors for quantum low-density parity-check codes with logarithmic or larger distances. These threshold estimates are parametrically better than the existing analytical bound based on percolation.

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Spin Glass Reflection Of The Decoding Transition For Quantum Error Correcting Codes, Alexey Kovalev, Leonid P. Pryadko Jan 2015

Spin Glass Reflection Of The Decoding Transition For Quantum Error Correcting Codes, Alexey Kovalev, Leonid P. Pryadko

Department of Physics and Astronomy: Faculty Publications

We study the decoding transition for quantum error correcting codes with the help of a mapping to random-bond Wegner spin models. Families of quantum low density parity-check (LDPC) codes with a finite decoding threshold lead to both known models (e.g., random bond Ising and random plaquette Z2 gauge models) as well as unexplored earlier generally non-local disordered spin models with non-trivial phase diagrams. The decoding transition corresponds to a transition from the ordered phase by proliferation of "post-topological" extended defects which generalize the notion of domain walls to non-local spin models. In recently discovered quantum LDPC code families with …

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