arXiv subjects

James W. Reiner

Publications and source records attributed to James W. Reiner.

15 recordsLinked to original sources

arXiv2023

A Compact Model of Threshold Switching Devices for Efficient Circuit Simulations

In this paper, we present a new compact model of threshold switching devices which is suitable for efficient circuit-level simulations. First, a macro model, based on a compact transistor based circuit, was implemented in LTSPICE. Then, a descriptive model was extracted and implemented in MATLAB, which is based on the macro model. This macro model was extended to develop a physical model that describes the processes that occur during the threshold switching. The physical model derived comprises a delay structure with few electrical components adjacent to the second junction. The delay model incorporates an internal state variable, which is crucial to transform the descriptive model into a compact model and to parameterize it in terms of electrical parameters that represent the component's behavior. Finally, we applied our model by fitting measured i-v data of an OTS device manufactured by Western Digital Research.

cond-mat.mes-hall↗

arXiv2014

Monitoring superparamagnetic Langevin behavior of individual ${\rm SrRuO_3}$ nanostructures

Patterned nanostructures on the order of 200 nm $\times$ 200 nm of the itinerant ferromagnet ${\rm SrRuO_3}$ give rise to superparamagnetic behavior below the Curie temperature (${\rm \sim 150 \ K}$) down to a sample-dependent blocking temperature. We monitor the superparamagnetic fluctuations of an individual volume and demonstrate that the field dependence of the time-averaged magnetization is well described by the Langevin equation. On the other hand, the rate of the fluctuations suggests that the volume in which the magnetization fluctuates is smaller by more than an order of magnitude. We suggest that switching via nucleation followed by propagation gives rise to Langevin behavior of the total volume, whereas the switching rate is determined by a much smaller nucleation volume.

cond-mat.mes-hall↗

arXiv2014

Active silicon integrated nanophotonics: ferroelectric BaTiO3 devices

The integration of complex oxides on silicon presents opportunities to extend and enhance silicon technology with novel electronic, magnetic, and photonic properties. Among these materials, barium titanate (BaTiO3) is a particularly strong ferroelectric perovskite oxide with attractive dielectric and electro-optic properties. Here we demonstrate nanophotonic circuits incorporating ferroelectric BaTiO3 thin films on the ubiquitous silicon-on-insulator (SOI) platform. We grow epitaxial, single-crystalline BaTiO3 directly on SOI and engineer integrated waveguide structures that simultaneously confine light and an RF electric field in the BaTiO3 layer. Using on-chip photonic interferometers, we extract a large effective Pockels coefficient of 213 plus minus 49 pm/V, a value more than six times larger than found in commercial optical modulators based on lithium niobate. The monolithically integrated BaTiO3 optical modulators show modulation bandwidth in the gigahertz regime, which is promising for broadband applications.

cond-mat.mtrl-sci↗

arXiv2013

Thermally assisted current-induced magnetization reversal in SrRuO3

We inject a sequence of 1 ms current pulses into uniformly magnetized patterns of the itinerant ferromagnet SrRuO3 until a magnetization reversal is detected. We detect the effective temperature during the pulse and find that the cumulative pulse time required to induce magnetization reversal depends exponentially on 1/T. In addition, we find that the cumulative pulse time also depends exponentially on the current amplitude. These observations indicate current-induced magnetization reversal assisted by thermal fluctuations.

cond-mat.mtrl-sci↗

arXiv2012

Indication for macroscopic quantum tunneling below 10 K in nanostructures of SrRuO3

We study magnetization reversal of nanostructures of the itinerant ferromagnet SrRuO3 (Tc~150 K). We find that down to 10 K the magnetization reversal is dominated by thermal activation. From 2 - 10 K, the magnetization reversal becomes independent of temperature, raising the possibility for reversal dominated by macroscopic quantum tunneling (MQT). A 10 K crossover to MQT is consistent with the extremely large anisotropy field (~7 T) of SrRuO3.

cond-mat.mes-hall↗

arXiv2012

Current-induced magnetization reversal in SrRuO3

We inject current pulses into uniformly magnetized patterns of thin films of the itinerant ferromagnet SrRuO3, while monitoring the effective temperature of the patterns during the current injection. We gradually increase the amplitude of the pulses until magnetization reversal occurs. We observe magnetization reversal induced by current above a temperature-dependent threshold and show that this effect is not simply due to sample heating or Oersted fields. We discuss the applicability of the current-induced spin-wave instability scenario.

cond-mat.str-el↗

arXiv2011

Scaling and field-induced crossover of the anomalous Hall effect in SrRuO3

We measure the anomalous Hall effect (AHE) resistivity $ρ_{xy}$ in thin films of the itinerant ferromagnet SrRuO$_{3}$. At low temperatures, the AHE coefficient $R_{s}$ varies with $ρ_{xx}^2$ in agreement with side jumps and Berry phase models. At higher temperatures, $R_{s}$ reaches a peak and then changes sign just below $T_{c}$. We find that for all films studied $R_{s}$ scales with resistivity in the entire ferromagnetic phase. SrRuO$_{3}$ films with very low residual resistivity exhibit field induced sign changes of the AHE at low temperatures, suggesting an $ω_c τ$ related crossover.

cond-mat.str-el↗

arXiv2011

Scaling of the anomalous Hall effect in SrRuO$_{3}$

We measure the anomalous Hall effect (AHE) resistivity $ρ_{xy}$ in thin films of the itinerant ferromagnet SrRuO$_{3}$. At low temperatures, the AHE coefficient $R_{s}$ varies with $ρ_{xx}^2$, and at higher temperatures, $R_{s}$ reaches a peak and then changes sign just below $T_{c}$. We find that for all films studied $R_{s}$ scales with resistivity in the entire ferromagnetic phase. We attribute the observed behavior to the contribution of the extrinsic side jumps mechanism and the intrinsic Karplus-Luttinger (Berry phase) mechanism including the effect of finite scattering rates.

cond-mat.str-el↗

arXiv2009

Field induced resistivity anisotropy in SrRuO3 films

SrRuO3 is an itinerant ferromagnet with orthorhombic structure and uniaxial magnetocrystalline anisotropy - features expected to yield resistivity anisotropy. Here we explore changes in the resistivity anisotropy of epitaxial SrRuO3 films due to induced magnetization in the paramagnetic state by using the planar Hall effect. We find that the effect of the induced magnetization on the in-plane anisotropy is strongly angular dependent, and we provide a full description of this behavior at 160 K for induced magnetization in the (001) plane.

cond-mat.str-el↗

arXiv2007

Efficient current-induced domain-wall displacement SrRuO3

We demonstrate current-induced displacement of ferromagnetic domain walls in sub-micrometer fabricated patterns of SrRuO3 films. The displacement, monitored by measuring the extraordinary Hall effect, is induced at zero applied magnetic field and its direction is reversed when the current is reversed. We find that current density in the range of 10^9 - 10^10 A/m^2 is sufficient for domain-wall displacement when the depinning field varies between 50 to 500 Oe. These results indicate relatively high efficiency of the current in displacing domain walls which we believe is related to the narrow width ~3 nm of domain walls in this compound.

cond-mat.other↗

arXiv2006

Determination of the resistivity anisotropy of SrRuO$_{3}$ by measuring the planar Hall effect

We have measured the planar Hall effect in epitaxial thin films of the itinerant ferromagnet SrRuO3 patterned with their current paths at different angles relative to the crystallographic axes. Based on the results, we have determined that SrRuO3 exhibits small resistivity anisotropy in the entire temperature range of our measurements (between 2 to 300 K); namely, both above and below its Curie temperature (~150 K). It means that in addition to anisotropy related to magnetism, the resistivity anisotropy of SrRuO3 has an intrinsic, nonmagnetic source. We have found that the two sources of anisotropy have competing effects.

cond-mat.other↗

arXiv2004

Testing the Berry phase model for extraordinary Hall effect in SrRuO3

Recently it has been suggested that the complicated temperature dependence of the extraordinary Hall effect (EHE) in the itinerant ferromagnet SrRuO3 could be explained by the Berry phase effect in the crystal momentum space. We test this model by measurements of EHE as a function of an applied magnetic field at a constant temperature and show that the results seem to contradict the Berry phase mechanism.

cond-mat.mtrl-sci↗

arXiv2003

Paramagnetic anisotropic magnetoresistance in thin films of SrRuO3

SrRuO3 is an itinerant ferromagnet and in its thin film form when grown on miscut SrTiO3 it has Tc of ~ 150 K and strong uniaxial anisotropy. We measured both the Hall effect and the magnetoresistance (MR) of the films as a function of the angle between the applied field and the normal to the films at temperatures above Tc. We extracted the extraordinary Hall effect that is proportional to the perpendicular component of the magnetization and thus the MR for each angle of the applied field could be correlated with the magnitude and orientation of the induced magnetization. We successfully fit the MR data with a second order magnetization expansion, which indicates large anisotropic MR in the paramagnetic state. The extremum values of resistivity are not obtained for currents parallel or perpendicular to the magnetization, probably due to the crystal symmetry.

cond-mat.mtrl-sci↗

arXiv2003

Large anisotropy in the paramagnetic susceptibility of SrRuO3 films

By using the extraordinary Hall effect in SrRuO3 films we performed sensitive measurements of the paramagnetic susceptibility in this itinerant ferromagnet, from Tc (~ 150 K) to 300 K. These measurements, combined with measurements of magnetoresistance, reveal that the susceptibility, which is almost isotropic at 300 K, becomes highly anisotropic as the temperature is lowered, diverging along a single crystallographic direction in the vicinity of Tc. The results provide a striking manifestation of the effect of exceptionally large magnetocrystalline anisotropy in the paramagnetic state of a 4d itinerant ferromagnet.

cond-mat.mtrl-sci↗

arXiv2003

Angular dependence of domain wall resistivity in SrRuO$_{\bf 3}$ films

${\rm SrRuO_3}$ is a 4d itinerant ferromagnet (T$_{c}$ $\sim $150 K) with stripe domain structure. Using high-quality thin films of SrRuO$_{3}$ we study the resistivity induced by its very narrow ($\sim 3$ nm) Bloch domain walls, $ρ_{DW}$ (DWR), at temperatures between 2 K and T$_{c}$ as a function of the angle, $θ$, between the electric current and the ferromagnetic domains walls. We find that $ρ_{DW}(T,θ)=\sin^2θρ_{DW}(T,90)+B(θ)ρ_{DW}(T,0)$ which provides the first experimental indication that the angular dependence of spin accumulation contribution to DWR is $\sin^2θ$. We expect magnetic multilayers to exhibit a similar behavior.

cond-mat.str-el↗