ESR spectrometer with a loop-gap resonator for cw and time resolved studies in a superconducting magnet

Abstract

The design and performance of an electron spin resonance spectrometer operating at 3 and 9 GHz microwave frequencies combined with a 9 T superconducting magnet is described. The probehead contains a compact two-loop, one gap resonator and is embedded in the variable temperature insert of the magnet enabling measurements in the 0-9 T magnetic field and 1.5-400 K temperature range. The spectrometer allows studies on systems where resonance occurs at fields far above the g ≈ 2 paramagnetic condition such as in strongly interacting spin systems. The low quality factor of the resonator allows time resolved experiments such as e.g. longitudinally detected ESR. We demonstrate the performance of the spectrometer on the MgB2 superconductor and the RbC60 conducting alkaline fulleride polymer.

Defect structure of ultrafine MgB2 nanoparticles

“…So far, very limited works have been presented for investigating the defect structure by the aid of EPR. Most of the works [15][16][17][18][19][20][21] have been dealt with the superconducting critical transition temperature or spin susceptibility at low temperatures. Thus, the defect structure of the pure MgB 2 at room temperature remained unclear.…”

Microwave frequency modulation in continuous-wave far-infrared ESR utilizing a quasi-optical reflection bridge

“…From the experimental standpoint, the polycrystalline KC 60 sample features a strong, nearly Lorentzian-shaped CESR signal, which can readily be observed at room temperature. For this reason, this material has already been used for the calibration of several ESR systems [6,7]. It has 0.75 mT (21.02 MHz) peak-to-peak linewidth at 209.6 GHz.…”

“…Other benefits of the frequency-modulation scheme are uniform modulation over the volume measured, freedom from microphonic noise and mechanical vibration due to the absence of magnetic field modulation. The FM method can also solve the problem of heating in the modulation coils, and is therefore strongly applicable to 7 high-pressure ESR measurements, where using modulation coils inside the pressure cell presents one of the biggest technical difficulties.…”

Continuous-wave far-infrared ESR spectrometer for high-pressure measurements

“…When measured at low microwave frequency of 9 GHz, at room temperature and ambient pressure, the fine powder of KC 60 yields a strong and relatively narrow CESR signal (DH $ 0.45 mT) [17]. For these reasons, KC 60 has already been used for calibration of other ESR systems [17,27]. Previous studies of the magnetic susceptibility and electrical transport properties in a wide temperature range (50-350 K) confirmed the metallic-type behavior of the orthorhombic phase KC 60 [28].…”