A. Wirthmann

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

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

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.

Electrical detection of microwave assisted magnetization switching in a Permalloy microstrip

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.

Electric detection of ferromagnetic resonance in single crystal iron film

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

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 2–18.5GHz 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.

Electrical detection of large cone angle spin precession from the linear to the nonlinear regime

The spin precession cone angle in a 5 μm wide Py microstrip has been investigated systematically from the linear to the nonlinear regime. At low power excitations, the cone angle increases linearly with the amplitude of the microwave magnetic field h. However, when h exceeds a critical value, a foldover resonance lineshape shows up, and the precession cone angle starts to increase with h1/3. The maximum cone angle reported in the present study reaches 22°.