Multipurpose High Frequency Electron Spin Resonance Spectrometer for Condensed Matter Research

We describe a quasi-optical multifrequency ESR spectrometer operating in the 75-225 GHz range and optimized at 210 GHz for general use in condensed matter physics, chemistry and biology. The quasi-optical bridge detects the change of mm wave polarization at the ESR. A controllable reference arm maintains a mm wave bias at the detector. The attained sensitivity of 2x10^10 spin/G/(Hz)1/2, measured on a dilute Mn:MgO sample in a non-resonant probe head at 222.4 GHz and 300 K, is comparable to commercial high sensitive X band spectrometers. The spectrometer has a Fabry-Perot resonator based probe head to measure aqueous solutions, and a probe head to measure magnetic field angular dependence of single crystals. The spectrometer is robust and easy to use and may be operated by undergraduate students. Its performance is demonstrated by examples from various fields of condensed matter physics.Comment: submitted to Journal of Magnetic Resonanc

Pulsed-magnetic-field measurements of Hall potential oscillations in alpha-(BEDT-TTF)(2)TlHg(SCN)(4) within the quantum Hall regime

Using a variant of the Corbino geometry in pulsed magnetic fields of up to 60 T, we have made direct measurements of the Hall potential in α-(BEDT-TTF)2TIHg(SCN)4 within the quantum Hall regime. This method enables the in-plane components of the resistivity tensor, which are normally very difficult to measure, to be investigated and the nonlinear behavior of the sample's I-V characteristics to be studied. It is found that an increasing probability of magnetic breakdown at higher fields leads to a degradation of the quantum Hall effect. ©1999 The American Physical Society

Resonant magnetoabsorption of millimeter-wave radiation in the quasi-two-dimensional organic metals alpha -(BEDT-TTF)2MHg(SCN)4 (M=K,Tl).

The magnetoabsorption of millimeter-wave radiation by single crystals of the organic metals α-(BEDT-TTF)2TlHg(SCN)4 and α-(BEDT-TTF)2KHg(SCN)4 has been studied in the frequency range 30-120 GHz. The experiments reveal two dominant contributions to the magnetoabsorption spectra. The first is interpreted as the cyclotron resonance of two-dimensional carriers, and is characterized by broad lines (linewidth/magnetic field ΔB/B∼0.5-1). In addition to a resonance exhibiting a cyclotron mass mc∼2.8m0, there are two further lines corresponding to frequency-dependent cyclotron masses in the ranges mc∼(1-1.5)m0 and mc∼(0.5-0.8)m0. This frequency dependence is believed to result from many-body effects. The second contribution to the magnetoabsorption is formed by a series of narrow lines with ΔB/B∼0.03-0.1 and amplitudes 5-10 times smaller than the features interpreted as cyclotron resonances. These narrow lines are attributed to a superposition of modes due to antiferromagnetic resonance and conduction-electron-spin resonance (ESR). The feature characteristic of antiferromagnetic resonance is the presence of a mode with a frequency that decreases with increasing magnetic field. The magnetoabsorption structure attributed to ESR consists of a relatively broad maximum upon which a sharp dip is superimposed. This behavior is believed to be analogous to the resonant transparency observed in thin metallic films undergoing ESR