Experimental Physics of Functional Spin Systems

Course with Participations of Group Members

Offers for Theses in the Group

Anomalous Hall torques in fully epitaxial heterostructures

The anomalous Hall effect (AHE), i.e., an additional Hall resistivity induced by the magnetization m in ferromagnetic materials, is a well-known effect. Although it was discovered more than a century ago, we deeply understood the underlying mechanism only recently. Experimentally, for most cases, this effect is discussed in term of generating transverse voltages or currents. In this Master thesis, we would like to demonstrate an unexplored property of the AHE: i.e., can the anomalous Hall effect generate a spin current and subsequently switch the magnetization of an ajacent ferromagnet? The prototypical sample is a fully epitaxial Fe/GaAs/GaMnAs heterostructure grown by molecular beam epitaxy, and the Hall bar device will be fabricated by electron-beam lithography.

suitable as

• Master’s Thesis Condensed Matter Physics

Supervisor: Christian Back

Manipulation of interfacial spin-orbit interaction via the electronic density of states

Several years ago, we have shown that robust spin-orbit fields (SOFs) exist at the single crystalline Fe/GaAs interface. The SOFs originate from Byckov-Rashba and Dresselhaus spin-orbit interaction due to the reduced symmetry at the interface, and have the following properties: 1) The in-plane SOF is proportional to density of states (DOS) at Fermi level (EF). 2) The out-of-plane SOF is proportional to all the states below EF. It is well known that in the CoFe alloys the DOS at EF depends strongly on the relative concentrations. Therefore, it is expected that the interfacial SOFs can be manipulated by Co alloying. In this Master thesis, we will address the following points: 1) We will replace Fe by FexCo1-x, and carry out spin-orbit torque ferromagnetic resonance (SOT-FMR) measurements. 2) To prove that the SOFs can be modulated by Co alloying 3) If the above question is answered positively, we will try to switch the magnetization direction using a d.c. current.

suitable as

• Master’s Thesis Condensed Matter Physics

Supervisor: Christian Back

Tracing in-plane magnetization switching dynamics by time-resolved magneto-optical Kerr microscopy

The demonstration of magnetization switching induced by spin-orbit torques in a ferromagnetic metal (FM)/heavy metal (HM) bilayer has attracted tremendous attention due to possible application in magnetic random access memories (MRAM). Typically, an in-plane current sent through the heavy metal layer (e.g. Pt) gives rise to a spin accumulation at the FM/HM interface due to the spin Hall effect. The spin accumulation acts on the ferromagnet (e.g. Co) via the spin transfer torque effect and leads to magnetization dynamics and, ideally, to switching. In this Master thesis, we will use time resolved magneto-optical Kerr microscopy (TRMOKE), which is a time and spatially resolved technique, to trace the switching dynamics of an in-plane magnetized ferromagnetic metal. The following points will be addressed: 1) The Co/Pt thin films will be patterned to micrometer-size devices by using a by mask-free laser writer or by electron-beam lithography. 2) Time and spatially resolved magnetization dynamics will be measured by TRMOKE. 3) Finally, the experimental data will be compared to theory.

suitable as

• Master’s Thesis Condensed Matter Physics

Supervisor: Christian Back

Current and Finished Theses in the Group