  Understanding and controlling the interfacial magnetic properties of
ferromagnetic thin films are crucial for spintronic device applications.
However, using conventional magnetometry, it is difficult to detect them
separately from the bulk properties. Here, by utilizing tunneling anisotropic
magnetoresistance in a single-barrier heterostructure composed of
La0.6Sr0.4MnO3 (LSMO)/ LaAlO3 (LAO)/ Nb-doped SrTiO3 (001), we reveal the
presence of a peculiar strong two-fold magnetic anisotropy (MA) along the
[110]c direction at the LSMO/LAO interface, which is not observed in bulk LSMO.
This MA shows unknown behavior that the easy magnetization axis rotates by
90{\deg} at an energy of 0.2 eV below the Fermi level in LSMO. We attribute
this phenomenon to the transition between the eg and t2g bands at the LSMO
interface. Our finding and approach to understanding the energy dependence of
the MA demonstrate a new possibility of efficient control of the interfacial
magnetic properties by controlling the band structures of oxide
heterostructures.
