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This paper presents an experimental and theoretical study of distance vs voltage characteristics of Au/Au tunnel junctions in air and UHV. Qualitative and quantitative results are compared with the classical models of Tersoff and Hamann and Simmons. To fit experimental conditions, the Simmons model has been extended in three dimensions using a hyperboloidal tip. However, a large discrepancy between theoretical and experimental quantitative results has been found in air because of barrier height lowering due to electrode contamination. An experimental rescaling factor is used in the modified Simmons model to fit any s(V) curve with high accuracy. These results are mainly interpreted in terms of gold surface elastic deformations. ͓S0163-1829͑99͒11635-7͔

We report an in situ observation of temperature-dependent phase transition in MnAs thin film by transmission electron microscopy (TEM) techniques. Following the identification of the crystallographic transition, from hexagonal α-MnAs to quasihexagonal β-MnAs, the orbital-to-spin moment ratio is measured and a breaking of the ferromagnetic order locally observed, thanks to the electron magnetic chiral dichroism (EMCD) technique. To achieve quantitative information, applying the sum rules to the dichroic signal of magnetic anisotropic materials is accurately discussed. Finally, the orbital-to-spin moment ratio of α-MnAs along the easy, hard, and intermediate magnetic axes is estimated by EMCD and compared to implemented density functional theory (DFT) calculations. The influence of the magnetocrystalline anisotropy is locally demonstrated. This work in particular illustrates the feasibility of the EMCD technique for in situ experiments, and proves its potential to explore the anisotropy of magnetic materials.