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The geometric structure of MgO deposited on Fe(001) in ultrahigh vacuum by electron evaporation was determined in detail by using surface x-ray diffraction. In contrast to the common belief that MgO grows in direct contact on the Fe(001) substrate, we find an FeO interface layer between the substrate and the growing MgO structure which has not been considered thus far. This result opens new perspectives for the understanding of the Fe/MgO/Fe(001) interface and the tunneling magnetoresistance effect in general.

Spin injection across the ferrimagnetic insulator yttrium iron garnet (YIG)/normal metal Au interface was studied using ferromagnetic resonance. The spin mixing conductance was determined by comparing the Gilbert damping parameter α in YIG/Au and YIG/Au/Fe heterostructures. The main purpose of this study was to correlate the spin pumping efficiency with chemical modifications of the YIG film surface using in situ etching and deposition techniques. By means of Ar+ ion beam etching, one is able to increase the spin mixing conductance at the YIG/Au interface by a factor of 5 compared to the untreated YIG/Au interface.

Klaua, M.; Ullmann, D.; Barthel, J.; Wulfhekel, W.; Kirschner, J.; Urban, R.; Monchesky, Theodore L.; Enders, Axel; Cochran, John F.; and Heinrich, Brett, "Growth, structure, electronic, and magnetic properties of MgO/Fe(001) Single-crystal epitaxial MgO thin films were grown directly onto high-quality Fe single crystal and Fe whisker substrates and covered with Fe/Au layers. Reflection high-energy electron diffraction and low-energy electron diffraction patterns and scanning tunneling microscopy images showed that the growth of MgO proceeded pseudomorphically in a nearly layer-by-layer mode up to six monolayers. A misfit dislocation network is formed for MgO layers thicker than six monolayers. The thin MgO films were characterized electrically by scanning tunneling spectroscopy. The tunneling barrier in MgO was found to depend on the MgO layer thickness, starting from 2.5 eV at two monolayer thickness to the expected full barrier of MgO of 3.6 eV at six monolayers. A small fraction of the scanned area showed randomly placed spikes in the tunneling conductance. Tunneling I-V curves at the defects showed a lower tunneling barrier than that in the majority of the MgO film. The total tunneling current integrated over areas of 100ϫ100 nm 2 , however, was not dominated by spikes of higher conductance. These local defects in the MgO barrier were neither related to atomic steps on the Fe substrates nor to individual misfit dislocations. Magnetic anisotropies and exchange coupling in Fe/ MgO͑001͒ and Fe/MgO/Fe͑001͒ structures were studied using ferromagnetic resonance and Brillouin light scattering.

We have grown epitaxial single-crystal magnetotunnel junctions using Fe͑001͒ substrates, MgO͑001͒ spacers and Fe top electrodes. We have used scanning tunneling microscopy and atomic force microscopy to measure the tunneling characteristics as a function of position and demonstrated that local tunneling can be obtained such that the buried MgO can be characterized with nm resolution. Local I(V) curves revealed that most of the area had intrinsic tunneling properties corresponding to the proper MgO tunneling barrier. A small fraction of the scanned areas showed localized spikes in the tunneling current which are most likely caused by defects in the MgO.