Angle-dependent magnetoresistance in epitaxially strain-engineered thin films

This thesis reports on magnetoresistance studies in strained thin films of La0.67Sr0.33MnO3 (LSMO) on LaAlO3 and SrTiO3. Strain-engineering thin films is a method to alter material properties such as the magnetization and electronic transport to alter them to a more desirable state.
In this thesis, the magnetic anisotropy of the films by varying temperature, applied magnetic field and the angle between current and field in etched LSMO Hall bars is studied.
Based on these studies three different magnetic phases when rotating the magnetic field in-plane. At temperatures between 10 to 125 K, a fourfold symmetry is observed, indicating a biaxial anisotropy parallel to the (110) and (1-10) directions . A second magnetic phase between 125 K to 250 K is observed and characterized by a twofold in-plane angle-dependent magnetoresistance signal. Increasing the temperature, leads to a paramagnetic insulating phase. The results show that the temperature variation of the angular dependence of the magnetoresistance is a reliable and alternative approach to study the different kinds of anisotropy induced in such strained oxide films and can complement torque-based magnetometry studies.
In the second angle-dependent study (chapter 5) the aim was to find the strain at which the magnetic easy-axis would rotate out-of-plane. The strong (1.9%) compressive strain indeed caused the magnetic easy axis to point in the out-of-plane direction and remain present up to 80 K. The observed trend indicates a gradual change from in-plane to out-of-plane anisotropy with increasing compressive strain.