arXiv subjects

C. -M. Hu

Publications and source records attributed to C. -M. Hu.

34 records · Page 2Linked to original sources

arXiv2015

On-chip artificial magnon-polariton device for voltage control of electromagnetically induced transparency

We demonstrate an on-chip device utilizing the concept of artificial cavity magnon-polariton (CMP) coupling between the microwave cavity mode and the dynamics of the artificial magnetism in a split ring resonator. This on-chip device allows the easy tuning of the artificial CMP gap by using a DC voltage signal, which enables tuneable electrodynamically induced transparency. The high tunability of the artificial magnon-polariton system not only enables the study of the characteristic phenomena associated with distinct coupling regimes, but also may open up avenues for designing novel microwave devices and ultra-sensitive sensors.

cond-mat.mtrl-sci↗

arXiv2015

High sensitivity microwave detection using a magnetic tunnel junction in the absence of an external applied magnetic field

In the absence of any external applied magnetic field, we have found that a magnetic tunnel junction (MTJ) can produce a significant output direct voltage under microwave radiation at frequencies, which are far from the ferromagnetic resonance condition, and this voltage signal can be increase by at least an order of magnitude by applying a direct current bias. The enhancement of the microwave detection can be explained by the nonlinear resistance/conductance of the MTJs. Our estimation suggests that optimized MTJs should achieve sensitivities for non-resonant broadband microwave detection of about 5,000 mV/mW.

cond-mat.mes-hall↗

arXiv2015

Quantifying the complex permittivity and permeability of magnetic nanoparticles

The complex permittivity and permeability of superparamagnetic iron-oxide nanoparticles has been quantified using a circular waveguide assembly with a static magnetic field to align the nanoparticle's magnetization. The high sensitivity of the measurement provides the precise resonant feature of nanoparticles. The complex permeability in the vicinity of ferromagnetic resonance (FMR) is in agreement with the nanoparticle's measured magnetization via conventional magnetometry. A rigorous and self-consistent measure of complex permittivities and permeabilities of nanoparticles is crucial to ascertain accurately the dielectric behaviour as well as the frequency response of nanoparticle magnetization, necessary ingredients when designing and optimizing magnetic nanoparticles for biomedical applications.

cond-mat.mes-hall↗

arXiv2015

Spin Pumping in Electrodynamically Coupled Magnon-Photon Systems

We use electrical detection, in combination with microwave transmission, to investigate both resonant and non-resonant magnon-photon coupling at room temperature. Spin pumping in a dynamically coupled magnon-photon system is found to be distinctly different from previous experiments. Characteristic coupling features such as modes anti-crossing, line width evolution, peculiar line shape, and resonance broadening are systematically measured and consistently analyzed by a theoretical model set on the foundation of classical electrodynamic coupling. Our experimental and theoretical approach pave the way for pursuing microwave coherent manipulation of pure spin current via the combination of spin pumping and magnon-photon coupling.

cond-mat.mtrl-sci↗

arXiv2015

Spin rectification for collinear and non-collinear magnetization and external magnetic field configurations

Spin rectification in a single crystal Fe/Au/Fe sandwich is electrically detected for collinear and non-collinear magnetization and external magnetic field configurations. The line shape, line width and signal polarity are analysed. The spin rectication theory has been much extended by taking the magneto-crystalline anisotropy and shape anisotropy into account, which explained non-collinear resonances and agrees very well with experimental data. Thus, a comprehensive understanding of spin rectification in ferromagnetic metal was demonstrated in this work.

cond-mat.mes-hall↗

arXiv2013

A Universal Method for Separating Spin Pumping from Spin Rectification Voltage of Ferromagnetic Resonance

We develop a method for universally resolving the important issue of separating spin pumping (SP) from spin rectification (SR) signals in bilayer spintronics devices. This method is based on the characteristic distinction of SP and SR, as revealed in their different angular and field symmetries. It applies generally for analyzing charge voltages in bilayers induced by the ferromagnetic resonance (FMR), independent of FMR line shape. Hence, it solves the outstanding problem that device specific microwave properties restrict the universal quantification of the spin Hall angle in bilayer devices via FMR experiments. Furthermore, it paves the way for directly measuring the nonlinear evolution of spin current generated by spin pumping. The spin Hall angle in a Py/Pt bilayer is thereby directly measured as 0.021$\pm$0.015 up to a large precession cone angle of about 20$^{\circ}$.

cond-mat.mtrl-sci↗

arXiv2013

Electrical Detection of Direct and Alternating Spin Current Injected from a Ferromagnetic Insulator into a Ferromagnetic Metal

We report room temperature electrical detection of spin injection from a ferromagnetic insulator (YIG) into a ferromagnetic metal (Permalloy, Py). Non-equilibrium spins with both static and precessional spin polarizations are dynamically generated by the ferromagnetic resonance of YIG magnetization, and electrically detected by Py as dc and ac spin currents, respectively. The dc spin current is electrically detected via the inverse spin Hall effect of Py, while the ac spin current is converted to a dc voltage via the spin rectification effect of Py which is resonantly enhanced by dynamic exchange interaction between the ac spin current and the Py magnetization. Our results reveal a new path for developing insulator spintronics, which is distinct from the prevalent but controversial approach of using Pt as the spin current detector.

cond-mat.mtrl-sci↗

arXiv2013

Rapid microwave phase detection based on a solid state spiontronic device

A technique for rapidly detecting microwave phase has been developed which uses a spintronic device that can directly rectify microwave fields into a dc voltage signal. Use of a voltage-controlled phase shifter enables the development of a spintronic device that can simultaneously 'read' the magnitude and phase of incident continuous-wave (CW) microwaves when combined with a lock-in amplifier. As an example of many possible practical applications of this device, the resonance phase in a complementary electric inductive-capacitive (CELC) resonator has been characterized using a spintronic sensor based on a magnetic tunnel junction (MTJ). This sensor device is not limited for use only with spintronic devices such as MTJs, but can also be used with semiconductor devices such as microwave detectors, and hence offers a useful alternative to existing microwave imaging and characterization technologies.

cond-mat.mes-hall↗

arXiv2011

On the line shape of the electrically detected ferromagnetic resonance

This work reviews and examines two particular issues related with the new technique of electrical detection of ferromagnetic resonance (FMR). This powerful technique has been broadly applied for studying magnetization and spin dynamics over the past few years. The first issue is the relation and distinction between different mechanisms that give rise to a photovoltage via FMR in composite magnetic structures, and the second is the proper analysis of the FMR line shape, which remains the "Achilles heel" in interpreting experimental results, especially for either studying the spin pumping effect or quantifying the spin Hall angles via the electrically detected FMR.

cond-mat.mtrl-sci↗

arXiv2008

Broadband electrical detection of spin excitations in (Ga,Mn)As using a photovoltage technique

We report on microwave photovoltage and simultaneous magnetotransport measurements in a (Ga,Mn)As film oriented normal to the magnetic field. We detect the ferromagnetic resonance over a broad frequency range of 2 GHz to 18.5 GHz and determine the spectroscopic g-factor and separate the Gilbert from the inhomogeneous contribution to magnetization relaxation. Temperature dependent measurements below the saturation magnetization indicate that the photovoltage signal can serve as a sensitive tool to study the crystal anisotropy. We demonstrate that the combination of spin dynamics with charge transport is a promising tool to study microstructured ferromagnetic semiconductor samples.

cond-mat.mtrl-sci↗

arXiv2008

Microwave photovoltage and photoresistance effects in ferromagnetic microstrips

We investigate the dc electric response induced by ferromagnetic resonance in ferromagnetic Permalloy (Ni80Fe20) microstrips. The resulting magnetization precession alters the angle of the magnetization with respect to both dc and rf current. Consequently the time averaged anisotropic magnetoresistance (AMR) changes (photoresistance). At the same time the time-dependent AMR oscillation rectifies a part of the rf current and induces a dc voltage (photovoltage). A phenomenological approach to magnetoresistance is used to describe the distinct characteristics of the photoresistance and photovoltage with a consistent formalism, which is found in excellent agreement with experiments performed on in-plane magnetized ferromagnetic microstrips. Application of the microwave photovoltage effect for rf magnetic field sensing is discussed.

cond-mat.str-el↗

arXiv2007

Quantized spin excitations in a ferromagnetic microstrip from microwave photovoltage measurements

Quantized spin excitations in a single ferromagnetic microstrip have been measured using the microwave photovoltage technique. Several kinds of spin wave modes due to different contributions of the dipole-dipole and the exchange interactions are observed. Among them are a series of distinct dipole-exchange spin wave modes, which allow us to determine precisely the subtle spin boundary condition. A comprehensive picture for quantized spin excitations in a ferromagnet with finite size is thereby established. The dispersions of the quantized spin wave modes have two different branches separated by the saturation magnetization.

cond-mat.str-el↗

arXiv2006

Realization of a Room-Temperature Spin Dynamo: The Spin Rectification Effect

We demonstrate a room temperature spin dynamo where the precession of electron spins in ferromagnets driven by microwaves manifests itself in a collective way by generating d.c. currents. The current/power ratio is at least three orders of magnitude larger than that found previously for spin-driven currents in semiconductors. The observed bipolar nature and intriguing symmetry are fully explained by the spin rectification effect via which the nonlinear combination of spin and charge dynamics creates d.c. currents.

cond-mat.mtrl-sci↗

arXiv2005

Resonances in Ferromagnetic Gratings Detected by Microwave Photoconductivity

We investigate the impact of microwave excited spin excitations on the DC charge transport in a ferromagnetic (FM) grating. We observe both resonant and nonresonant microwave photoresistance. Resonant features are identified as the ferromagnetic resonance (FMR) and ferromagnetic antiresonance (FMAR). A macroscopic model based on Maxwell and Landau-Lifschitz equations reveals the macroscopic nature of the FMAR. The experimental approach and results provide new insight in the interplay between photonic, spintronic, and charge effects in FM microstructures.

cond-mat.other↗

arXiv2004

Quantized Dispersion of Two-Dimensional Magnetoplasmons Detected by Photoconductivity Spectroscopy

We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect.

cond-mat.mes-hall↗

arXiv2003

Far-infrared photo-conductivity of electrons in an array of nano-structured antidots

We present far-infrared (FIR) photo-conductivity measurements for a two-dimensional electron gas in an array of nano-structured antidots. We detect, resistively and spectrally resolved, both the magnetoplasmon and the edge-magnetoplasmon modes. Temperature-dependent measurements demonstrates that both modes contribute to the photo resistance by heating the electron gas via resonant absorption of the FIR radiation. Influences of spin effect and phonon bands on the collective excitations in the antidot lattice are observed.

cond-mat.mes-hall↗