Experimental Evidence for Intra-Atomic Noncollinear Magnetism at Thin Film Probe Tips

The energy-dependent spin-density orientation (SDO) at the apex of thin magnetic film tips is studied by spin-polarized scanning tunneling spectroscopy (SP-STS) at different bias voltages. At most energies the SDO is collinear 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 is explained in terms of intra-atomic noncollinear magnetism.