Conduction-electron resonance linewidth in dilute magnetic alloys above the kondo critical field at very low temperatures

The zero-temperature transverse dynamic susceptibility at frequency Omega, chi(-)(e)(Omega), is calculated diagrammatically for conduction electrons in a dilute magnetic alloy. The static magnetic field is assumed to be sufficiently large to quench the Kondo divergence. The exchange interaction is treated to second order in the coupling constant J. It is found that the conduction-electron magnetic-resonance response is a 8 function at the exchange-"dressed" conduction-electron resonance frequency omega(e)', with a superimposed Lorentzian envelope centered at omega(e)', which is finite ("turns on") at frequencies Omega>omega(s), where omega(s) is the localized spin resonance frequency. The implications of this result are discussed with reference to the magnetic-resonance bottleneck, and previous (approximate) calculations of the zero-temperature magnetic-resonance response.