Point-contact spectroscopy of the interaction of electrons with magnetic impurities in metals

The stationary and nonstationary current-voltage characteristics of point-contacts made of magnetic alloys are determined by the method of quasiclassical Green’s function, integrated with respect to the energy variable. The cases of alloys with disordered (Kondo effect in a spatially nonuniform situation) and ordered magnetic impurities (point-contact spectroscopy of the ferromagnetic phase of spin glasses) are studied. In the case of disordered impurities, in the absence of an external magnetic field the second derivative of the stationary IVC has the form of a “negative zero-bias anomaly”—a minimum at eV∼ T. In the presence of an external magnetic field Q, aside from the Kondo minimum, there also appears on the second derivative of the IVC a maximum at eV∼ Q, formed by the inelastic scattering of electrons. In the case of ordered magnetic impurities the second derivative of the IVC has the form of a “positive zero-bias anomaly”—a maximum at eV∼ Qex, which is associated with the inelastic scattering of electrons by impurities located in the internal magnetic field Qex. It is shown that in the nonstationary case an external alternating signal with a frequency of the order of the energy at which the stationary IVC is nonlinear can be detected. The inductive component of the nonstationary current in the case of spin glasses has a nontrivial dependence on the constant bias, due to the renormalization of the electron mass as a result of the interaction of electrons with the magnetic impurities.