We describe the fabrication of multiterminal semiconductor/ferromagnet probes for a new technique to study magnetic nanostructures: spin-filter scanning tunneling microscopy. We describe the principle of the technique, which is based on spin-polarized tunneling and subsequent analysis of the spin polarization using spin-dependent transmission in the probe tip. We report the fabrication of the probes having a submicron semiconductor/ferromagnet heterostructure at the end of the tip.The continuous reduction in critical feature sizes in both magnetic data storage and semiconductor technologies requires characterization techniques with ever higher spatial resolution. The emerging field of spintronics 1 also requires appropriate techniques to study spin-related phenomena in magnetic nanostructures. 2 Scanning probe techniques 3 such as magnetic force microscopy ͑MFM͒ and spin-polarized scanning tunneling microscopy ͑SP-STM͒ are frequently employed. MFM is versatile because it does not require ultraclean nor conducting samples. However, as it relies on magnetic stray fields, the data interpretation are not always straightforward, while the typical best resolution is limited at around 20 nm, 4,5 which is close to the critical feature size in magnetic nanostructures.SP-STM is a powerful technique in terms of the wealth of electronic information it provides, including the position of exchange-split features in the local density of states ͑LDOS͒, 6 and has proven capable of the ultimate resolution by imaging magnets at the atomic scale. 7,8 SP-STM is usually performed in the differential conductivity mode 6 where its need for exchange-split states to produce strong features in the LDOS, low temperatures, and its spectroscopic nature limits its applicability and makes the extraction of quantitative magnetic information more difficult. To obtain the sample tunneling spin polarization ͑TSP͒ with SP-STM, one must know the corresponding TSP of the last atoms of the tip ͑magnitude and direction͒, which may not be a trivial matter. Thus, it would be highly desirable to have a technique capable of measuring directly and quantitatively the sample spin polarization at Fermi level and with atomic resolution. This is of importance for assessing spin transport in new materials and devices. 9 Here we propose a novel technique, namely, spin-filter scanning tunneling microscopy ͑SF-STM͒. As in SP-STM, this new technique relies on spin-polarized tunneling between tip and sample to extract magnetic information from surfaces. The difference is that in SF-STM, the spin analysis occurs within the tip in a semiconductor/ferromagnet heterostructure-after tunneling. The novel tip design consists of a top metallic surface where tunneling takes place, followed by a semiconductor/ferromagnet heterostructure in which transmission is spin dependent ͑see Fig. 1͒. There are two separate contacts to the tip, one to the metallic surface, the other to the semiconductor. Magnetic contrast is provided by the dc measurement of the current collected in the sem...

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