Experimentally, the Spin Reorientation Transition (SRT) process was developed by Gradmann et al. on NiFe layers on Cu (111). For some time now, the SRT has been reintroduced into the scientific focus, as the understanding of the SRT is the basis for the development of systems with vertical easy magnetization axis, which are of great importance, inter alia. for sensor applications as well as for the magnetic storage of data. For example, the memory density of a hard disk can be increased by a perpendicular magnetization of the bits due to the reduction of the area per bit as compared to hard disks with parallel magnetization (keyword: perpendicular recording)
The investigation of the spin-reorientation transition has brought substantial new findings in the field of thin-film magnetism in the past. So far, this phenomenon has been investigated mainly with laterally integrating measuring methods. In our approach we use spin-resolved scanning tunnel microscopy.
With this method, a resolution in the range of individual atoms can be achieved. We want to investigate the thickness-dependent and temperature-dependent spin-reorientation transition in epitaxial Fe / Mo (110) and Co / Mo (110) films. We pay particular attention to the temperature-dependent SRT as the temperature can be varied continuously as opposed to the layer thickness.
The aim of the project is to gain a microscopic understanding of the SRT.
a) Three-dimensional representation of a (600 x 600) nm2 STM scan with the spin polarized differential dI / dU conductivity map as a texture. The sample is evaporated with 1.5 ML Fe at room temperature and then annealed at 600 K. The measurement comditions were U = -0.7 V, I = 2.5 nA and T = 5 K sample temperature. The Fe double layer stripes show a clear magnetic contrast as well as offset lines. A domain wall is easily recognizable. Figures b-e) show a sequence of dI / dU images on the same sample site as a) recorded when the sample temperature is increased step by step. The magnetic contrast remains clearly visible up to a temperature of 13 K and disappears at 13.2 K. Double-pointed artifacts can be seen in the images d) - e) (marked by white arrows in d). In images c) and d), a magnetic contrast as well as a domain wall (marked with a green circle in d) can also be seen in the mono layer.