Experimental evidence for intra-atomic noncollinear magnetism at thin filmprobe tips

The energy-dependent spin-density orientation (SDO) at the apex of thin mag netic film tips is studied by spin-polarized scanning tunneling spectroscop y (SP-STS) at different bias voltages. At most energies the SDO is collinea r with the tip magnetization resulting in a domain or domain-wall contrast in SP-STS images of out-of-plane magnetized samples measured with Gd or Fe coated tips, respectively. For some bias voltages, however, the SDO of the tip is found to be almost perpendicular to its magnetization. This result i s explained in terms of intra-atomic noncollinear magnetism.