The theory of inhomogeneously broadened and hyperfine split EPR spectra in superconductors

The theory of EPR in type-II superconductors, developed previously (see ibid., vol.17, p.695, 1987), is extended to include the inhomogeneous broadening and hyperfine structure effects. The appropriate kinetic equations are obtained and solved describing the coupled motion of transverse magnetisation of conduction electrons and transverse magnetisation of magnetic impurities, subject to the action of static spatially random local fields. The solution is analysed analytically and numerically for specific local-field distribution functions. It is shown that even under very soft 'bottleneck' conditions the EPR line exhibits a sharp narrowing just below the superconducting transition temperature Tc. This narrowing occurs primarily because of the decreasing of the inhomogeneous linewidth due to 'superconducting' enhancement of the Korringa relaxation rate, which governs the degree of the narrowing under the bottleneck conditions. It is demonstrated how the exponential decrease of the relaxation rates at temperatures T<<Tc can be used to resolve the hyperfine structure and extract the splitting constant. The connection with experiment is discussed

Spin kinetics and EPR in superconductors

The theory of the electron paramagnetic resonance (EPR) on magnetic impurities in type-II superconductors is presented. The kinetic equations describing the coupled motion of the magnetisation of localised spins and that of conduction electrons' spins are derived and solved. Analytical expressions for the relaxation rates, being the real parts of kinetic coefficients entering the equations, are obtained. These expressions are valid at arbitrary temperatures and frequencies of resonance within the approximation of the homogeneous superconductor. The detailed numerical analysis, allowing the authors to plot the temperature dependence of the EPR linewidth, is carried out. It is shown that the 'electronic bottleneck effect' becomes stronger in the superconducting state and, as a result, the linewidth becomes a monotonic function of temperature. The EPR experiments on superconducting systems are discussed

The theory of inhomogeneously broadened and hyperfine split EPR spectra in superconductors

The theory of EPR in type-II superconductors, developed previously (see ibid., vol.17, p.695, 1987), is extended to include the inhomogeneous broadening and hyperfine structure effects. The appropriate kinetic equations are obtained and solved describing the coupled motion of transverse magnetisation of conduction electrons and transverse magnetisation of magnetic impurities, subject to the action of static spatially random local fields. The solution is analysed analytically and numerically for specific local-field distribution functions. It is shown that even under very soft 'bottleneck' conditions the EPR line exhibits a sharp narrowing just below the superconducting transition temperature Tc. This narrowing occurs primarily because of the decreasing of the inhomogeneous linewidth due to 'superconducting' enhancement of the Korringa relaxation rate, which governs the degree of the narrowing under the bottleneck conditions. It is demonstrated how the exponential decrease of the relaxation rates at temperatures T<<Tc can be used to resolve the hyperfine structure and extract the splitting constant. The connection with experiment is discussed

Spin kinetics and EPR in superconductors

The theory of the electron paramagnetic resonance (EPR) on magnetic impurities in type-II superconductors is presented. The kinetic equations describing the coupled motion of the magnetisation of localised spins and that of conduction electrons' spins are derived and solved. Analytical expressions for the relaxation rates, being the real parts of kinetic coefficients entering the equations, are obtained. These expressions are valid at arbitrary temperatures and frequencies of resonance within the approximation of the homogeneous superconductor. The detailed numerical analysis, allowing the authors to plot the temperature dependence of the EPR linewidth, is carried out. It is shown that the 'electronic bottleneck effect' becomes stronger in the superconducting state and, as a result, the linewidth becomes a monotonic function of temperature. The EPR experiments on superconducting systems are discussed

Spin kinetics and EPR in superconductors

The theory of the electron paramagnetic resonance (EPR) on magnetic impurities in type-II superconductors is presented. The kinetic equations describing the coupled motion of the magnetisation of localised spins and that of conduction electrons' spins are derived and solved. Analytical expressions for the relaxation rates, being the real parts of kinetic coefficients entering the equations, are obtained. These expressions are valid at arbitrary temperatures and frequencies of resonance within the approximation of the homogeneous superconductor. The detailed numerical analysis, allowing the authors to plot the temperature dependence of the EPR linewidth, is carried out. It is shown that the 'electronic bottleneck effect' becomes stronger in the superconducting state and, as a result, the linewidth becomes a monotonic function of temperature. The EPR experiments on superconducting systems are discussed

The theory of inhomogeneously broadened and hyperfine split EPR spectra in superconductors

The theory of EPR in type-II superconductors, developed previously (see ibid., vol.17, p.695, 1987), is extended to include the inhomogeneous broadening and hyperfine structure effects. The appropriate kinetic equations are obtained and solved describing the coupled motion of transverse magnetisation of conduction electrons and transverse magnetisation of magnetic impurities, subject to the action of static spatially random local fields. The solution is analysed analytically and numerically for specific local-field distribution functions. It is shown that even under very soft 'bottleneck' conditions the EPR line exhibits a sharp narrowing just below the superconducting transition temperature Tc. This narrowing occurs primarily because of the decreasing of the inhomogeneous linewidth due to 'superconducting' enhancement of the Korringa relaxation rate, which governs the degree of the narrowing under the bottleneck conditions. It is demonstrated how the exponential decrease of the relaxation rates at temperatures T<<Tc can be used to resolve the hyperfine structure and extract the splitting constant. The connection with experiment is discussed

The theory of inhomogeneously broadened and hyperfine split EPR spectra in superconductors

The theory of EPR in type-II superconductors, developed previously (see ibid., vol.17, p.695, 1987), is extended to include the inhomogeneous broadening and hyperfine structure effects. The appropriate kinetic equations are obtained and solved describing the coupled motion of transverse magnetisation of conduction electrons and transverse magnetisation of magnetic impurities, subject to the action of static spatially random local fields. The solution is analysed analytically and numerically for specific local-field distribution functions. It is shown that even under very soft 'bottleneck' conditions the EPR line exhibits a sharp narrowing just below the superconducting transition temperature Tc. This narrowing occurs primarily because of the decreasing of the inhomogeneous linewidth due to 'superconducting' enhancement of the Korringa relaxation rate, which governs the degree of the narrowing under the bottleneck conditions. It is demonstrated how the exponential decrease of the relaxation rates at temperatures T<<Tc can be used to resolve the hyperfine structure and extract the splitting constant. The connection with experiment is discussed

Spin kinetics and EPR in superconductors

The theory of the electron paramagnetic resonance (EPR) on magnetic impurities in type-II superconductors is presented. The kinetic equations describing the coupled motion of the magnetisation of localised spins and that of conduction electrons' spins are derived and solved. Analytical expressions for the relaxation rates, being the real parts of kinetic coefficients entering the equations, are obtained. These expressions are valid at arbitrary temperatures and frequencies of resonance within the approximation of the homogeneous superconductor. The detailed numerical analysis, allowing the authors to plot the temperature dependence of the EPR linewidth, is carried out. It is shown that the 'electronic bottleneck effect' becomes stronger in the superconducting state and, as a result, the linewidth becomes a monotonic function of temperature. The EPR experiments on superconducting systems are discussed