Abstract
We experimentally investigate the effect of resonant microwave absorption on the magneto-conductance of tunable Co/Pd point contacts. At the interface a non-equilibrium spin accumulation is created via microwave absorption and can be probed via point contact spectroscopy. We interpret the results as a signature of direct spin-flip excitations in Zeeman-split spin-subbands within the Pd normal metal part of the junction. The inverse effect, which is associated with the emission of a microwave photon in a ferromagnet/normal metal point contact, can also be detected via its unique signature in transport spectroscopy.
Highlights
In recent years, a multitude of novel devices has been proposed, which rely on the dynamic interplay between spin- and charge in metallic, magnetic nanostructures
That an out of plane polarisation of the Pd leads in vicinity of the atomic contact produces the zero-bias anomaly (ZBA) instead of a local magnetic moment at the last atom and a small, perpendicular magnetic field is required to rotate the magnetisation of the Pd leads
We investigate the signature of spin-flip photoemission in the point of contact (PC) conductance in contacts with sufficient stability, i.e. where no contact reorganisation takes place during the measurement, which often results in a sudden, permanent conductance change, i.e. when the magnetic field is swept
Summary
A multitude of novel devices has been proposed, which rely on the dynamic interplay between spin- and charge in metallic, magnetic nanostructures. A larger splitting, in the meV range, can be created in contacts incorporating dilute ferromagnets (f), where the spin-bands are split due to the quantum mechanical exchange interaction It was suggested, that stimulated emission of microwave and terahertz photons takes place upon relaxation, while the non-equilibrium distribution is maintained via continuous injection of hot electrons at current densities above 108 A cm−2, which is experimentally feasible in the point contact geometry [7, 11]. At least in principal, spin-flip photoemission in magnetic heterojunctions should be observable at room temperature [12] If realized such all-metallic spin-flip lasing devices would provide a fundamentally new type of highly tunable, miniaturised radiation source in the GHz and THz range with giant intensity compared to state of the art semiconductor quantum cascade lasers [8, 13]. Gulayev et al reported radiation from large contacts (>10 μm in Konstanzer Online-Publikations-System (KOPS) URL: http://nbn-resolving.de/urn:nbn:de:bsz:352-0-372954
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