Jeng-Bang Yau

Epitaxial growth of multiferroic YMnO3 on GaN

In this work, we report on the epitaxial growth of multiferroic YMnO3 on GaN. Both materials are hexagonal with a nominal lattice mismatch of 4%, yet x-ray diffraction reveals an unexpected 30° rotation between the unit cells of YMnO3 and GaN that results in a much larger lattice mismatch (10%) compared to the unrotated case. Estimates based on first principles calculations show that the bonding energy gained from the rotated atomic arrangement compensates for the increase in strain energy due to the larger lattice mismatch. Understanding the energy competition between chemical bonding energy and strain energy provides insight into the heteroepitaxial growth mechanisms of complex oxide-semiconductor systems.

Giant planar Hall effect in colossal magnetoresistive La0.84Sr0.16MnO3 thin films

The transverse resistivity in thin films of La0.84Sr0.16MnO3 (LSMO) exhibits sharp field-symmetric jumps below TC. We show that a likely source of this behavior is the giant planar Hall effect combined with biaxial magnetic anisotropy. The effect is comparable in magnitude to that observed recently in the magnetic semiconductor Ga(Mn)As. It can be potentially used in applications such as magnetic sensors and nonvolatile memory devices.

Anisotropic magnetoresistance in colossal magnetoresistive La1-xSrxMnO3 thin films

We report on magnetic field and temperature-dependent measurements of the anisotropic magnetoresistance (AMR) in epitaxial La1−xSrxMnO3 (LSMO) thin films. While in 3d ferromagnetic alloys increasing the magnetization, either by reducing the temperature or increasing the magnetic field, increases the AMR, we find that in LSMO films the AMR dependence on magnetization displays nonmonotonic behavior which becomes particularly pronounced in lightly doped compounds. We believe that this behavior is related to the inhomogeneity exhibited by these materials.

Planar Hall-effect magnetic random access memory

We suggest a type of magnetic random access memory (MRAM) that is based on the phenomenon of the planar Hall effect (PHE) in magnetic films, and we demonstrate this idea with manganite films. The PHE-MRAM is structurally simpler than the currently developed MRAM that is based on magnetoresistance tunnel junctions, with the tunnel junction structure being replaced by a single-layer film.