Miroslav Požek

EPR detection of the flux distribution in ceramic high-Tc superconductors

Abstract EPR measurements were made on adsorbed diphenyl picrylhydrazil (DPPH) at the surface of a ceramic high- T c superconductor YBa 2 Cu 3 O 7 . A significant broadening of the EPR linewidth was observed below the superconducting transition temperature T c . It is interpreted as a broadening due to the spatial distribution of the flux in the superconducting mixed state which is developed at the resonant magnetic field H 0 (H Cl ⪡ H 0 ⪡ H C2 ). The penetration depth of the magnetic field can be determined by this simple technique.

Effects of alternating magnetic fields on the microwave absorption in ceramic high-Tc superconductors

Abstract Microwave absorption in ceramic high-Tc superconductors shows a complex response to applied d.c. and a.c. magnetic fields. In the total absorption signal, one can identify a component which is due to the modulation of the magnetic flux through the sample, and components which depend on the boundary current.

Comparison of direct and modulated microwave magnetoresistance in ceramic and single crystal YBa2Cu3O7−δ

Abstract A comparative study of microwave absorption in single crystals and ceramic samples of YBa 2 Cu 3 O 7−δ has made it possible to distinghuish the processes in the bulk from those in the intergranular medium. The origin of various types of hysteresis in direct and modulated absorption singnals is clarified. The appearance of the modulation-dependent hysteresis is shown to be an evidence of anharmonicity in the pinning potential.

Field-modulated microwave absorption in granular superconductors: First and second harmonic signals

Abstract Field-modulated microwave absorption in granular superconductors is analyzed within the weak link model. The signals are calculated for various modulation amplitudes, both for the first and the second harmonic detection. The calculation signal shapes are in good agreement with experimental results.

An ac method for the precise measurement of Q-factor and resonance frequency of a microwave cavity

We have developed a new and fast method for the determination of the complex frequency shift of a microwave resonant cavity. The method is based on frequency modulation of the microwave source around the cavity resonance and detection of the 2nd and 4th harmonic of the modulation frequency. With this procedure the static measurement of the response amplitude is not necessary and all the data are obtained through a single ac channel. The optimal frequency deviation is shown to be comparable to the cavity resonance width.

Decoupled CuO 2 and RuO 2 layers in superconducting and magnetically ordered RuSr 2 GdCu 2 O 8

Comprehensive measurements of dc and ac susceptibility, dc resistance, magnetoresistance, Hall resistivity, and microwave absorption and dispersion in fields up to 8 T have been carried out on

Transport and microwave study of superconducting and magnetic RuSr 2 EuCu 2 O 8

{\mathrm{RuSr}}_{2}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}

Microwave surface impedence in the mixed state of type-II superconductors

with the aim to establish the properties of

Magnetic flux inhomogeneity in ceramic YBa2Cu3O7−δ superconductors studied by EPR

{\mathrm{RuO}}_{2}

A Magnetization and Microwave Study of Superconducting MgB2

and