Y. S. Gui

Microwave photovoltage and photoresistance effects in ferromagnetic microstrips

We investigate the dc electric response induced by ferromagnetic resonance in ferromagnetic Permalloy

The rf magnetic-field vector detector based on the spin rectification effect

({\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20})

Quantized spin excitations in a ferromagnetic microstrip from microwave photovoltage measurements.

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.

Electric field controlled reversible magnetic anisotropy switching studied by spin rectification

Ferromagnetic resonances on three Permalloy strips under an in-plane external magnetic field are detected electrically. By measuring and analyzing the angular dependence of the photovoltage induced by the spin rectification effect, an approach is demonstrated for making microwave detectors capable of detecting the rf magnetic field vector at subwavelength scale.

Electrical detection of the ferromagnetic resonance : Spin-rectification versus bolometric effect

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.

Electrical detection of microwave assisted magnetization switching in a Permalloy microstrip

In this letter, spin rectification was used to study the electric field controlled dynamic magnetic properties of the multiferroic composite which is a Co stripe with induced in-plane anisotropy deposited onto a Pb(Mg1∕3Nb2∕3)O3-PbTiO3 substrate. Due to the coupling between piezoelectric and magnetoelastic effects, a reversible in-plane anisotropy switching has been realized by varying the history of the applied electric field. This merit results from the electric hysteresis of the polarization in the nonlinear piezoelectric regime, which has been proved by a butterfly type electric field dependence of the in-plane anisotropy field. Moreover, the electric field dependent effective demagnetization field and linewidth have been observed at the same time.

Electric detection of ferromagnetic resonance in single crystal iron film

The authors have investigated the dc resistance change of a Permalloy microstrip under microwave irradiation. The experimental results demonstrate that both the spin-rectification and the bolometric effects significantly affect the dc resistance change, and the contribution of each can be precisely determined due to their different dependences on the modulation frequency of the microwave. Therefore, both the cone angle of magnetization precession and the thermal relaxation time following microwave heating are obtained.

Rapid microwave phase detection based on a solid state spintronic device

Microwave assisted magnetization switching has been investigated in a nonelliptic Permalloy microstrip, using radio frequency magnetic fields h applied in-plane perpendicular to the long axis of the strip. In low power excitations, Hs decreases almost linearly with increasing h; this can be qualitatively understood by introducing an susceptibility χyy that links the dynamic magnetization inside the microstip to the h field outside the microstip. However, at high frequencies, Hs no longer decrease with increasing h when this latter field exceeds a critical value. We suppose such “saturation” effects could attribute to the nonlinear ferromagnetic resonance caused by high power excitations.

Nondestructive two-dimensional phase imaging of embedded defects via on-chip spintronic sensor

We report electric detection of ferromagnetic resonance (FMR) in epitaxially grown single crystal iron film through microwave photovoltage generation technique. The experimental results agree well with the established theory about FMR in iron films, showing excellent extendability of such a technique onto different ferromagnets as an effective way to study magnetocrystalline anisotropy and spin excitations. Furthermore, the information about the phase of magnetization precession is implicated in the lineshape of photovoltage, which makes it possible to probe in details into magnetic phase dynamics that is of significance for devising spintronic devices.

Broadband electrical detection of spin excitations in Ga0.98Mn0.02As using a photovoltage technique

A technique for rapidly detecting microwave magnitude and phase has been developed using a spintronic device as a microwave sensor, which allows a lock-in amplifier to perform real-time microwave measurement. To demonstrate the feasibility and reliability of the proposed approach, the resonance including the amplitude and phase in a complementary electric inductive-capacitive resonator has been characterized. The results are in agreement with measurement preformed by a vector network. This sensor approach is not limited for use only with spintronic devices, but can also be used with semiconductor devices and hence offers a useful alternative to existing microwave imaging and characterization technologies.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.