Yuzi Liu

Microstructure analysis of a SmCo/Fe exchange spring bilayer

The microstructure of a magnetron sputtered Cr(20 nm)/Sm–Co(20 nm)/Fe(20 nm)/Cr(5 nm) exchange spring magnet was studied using an advanced analytical transmission electron microscopy to better understand the relationship between its chemistry and structure to enhance the energy product. It is shown that the Fe atoms diffuse into the well textured Sm–Co layer, causing a transition from the stoichiometric Sm2Co7 near the Sm–Co/Cr interface to a defected Sm(Co,Fe)5 in the Sm–Co–Fe intermixed area. The graded intermixed layer between Sm–Co and pure Fe gives rise to a compositionally enhanced energy product.

Effect of deposition temperature on surface morphology and magnetic properties in epitaxial CoFe2O4 thin films deposited by metal organic chemical vapor deposition

We have successfully grown epitaxial CoFe2O4 (CFO) thin film on SrTiO3 by metal organic chemical vapor deposition. In order to understand the surface structure and its correlation with magnetic properties, CFO thin films were deposited at a range of deposition temperatures. As the deposition temperature is decreased, a huge effect on film morphology and surface roughness is observed, resulting from a change in the size and density of the crystal nuclei. These changes to grain structure and surface roughness modify the energy landscape of the films and are major contributors to the change in magnetic properties as a function of deposition temperature: the direction of the easy axis is aligned in-plane at lower deposition temperatures and lower anisotropy between different directions is observed in the rough films grown at high temperature.We have successfully grown epitaxial CoFe2O4 (CFO) thin film on SrTiO3 by metal organic chemical vapor deposition. In order to understand the surface structure and its correlation with magnetic properties, CFO thin films were deposited at a range of deposition temperatures. As the deposition temperature is decreased, a huge effect on film morphology and surface roughness is observed, resulting from a change in the size and density of the crystal nuclei. These changes to grain structure and surface roughness modify the energy landscape of the films and are major contributors to the change in magnetic properties as a function of deposition temperature: the direction of the easy axis is aligned in-plane at lower deposition temperatures and lower anisotropy between different directions is observed in the rough films grown at high temperature.

The effect of CoPt crystallinity and grain texturing on properties of exchange-coupled Fe/CoPt systems

The effect of the crystallinity and the grain texturing of CoPt hard layers on exchange coupled Fe/CoPt soft/hard magnetic systems was studied using gradient thickness multilayer thin films. We have studied the hard layer structures by transmission electron microscopy and x-ray diffraction, and characterized the exchange coupling interaction through magnetization loops obtained by the magneto-optical Kerr effect measurement. We found that exchange coupling strongly depends on the crystalline characteristics of the CoPt hard layer. There is correlation between the mixture of different grain orientations of the CoPt hard layer and coupling efficiency. In particular, interlayer coupling is enhanced when there is only one orientation, namely, the L10 CoPt structure with its c-axis inclined at 45° with respect to the substrate plane. An increased degree of mixture of the latter with the in-plane-c-axis L10 CoPt structure is detrimental to obtaining one-phase-like magnetization loops. The present work points to...

Quantifying mean inner potential of ZnO nanowires by off-axis electron holography

Off-axis electron holography has been used to quantitatively determine the mean inner potential of ZnO. [0001] grown ZnO nanowires with hexagonal cross-sections were chosen as our samples because the angle between the adjacent surfaces is 120°, as confirmed by electron tomography, so the entire geometry of the nanowire could be precisely determined. The acceleration voltage of the transmission electron microscope was accurately calibrated by convergent beam electron diffraction (CBED)-higher-order Laue-zone (HOLZ) analyses. ZnO nanowires were tilted away from zone-axis to avoid strong dynamical diffraction effect, and the tilting angles were determined by CBED patterns. Our experimental data found a mean inner potential of ZnO as 14.30±0.28 V.

Solution growth of HgTe Nanoweires at lowtemperature

Large scale HgTe nanowires have been grown from Te nanowires by solution approach at low temperature. The widths are in the range 10–20 nm, with lengths up to 1µm. The nanowires have been characterized by uv - vis spectra, scanning electron microscopy, energy-disperse X-ray spectroscopy (EDS), transmission electron microscopy. The effects of growth temperature and time have been investigated and the best growth temperature is 80 – 90°C. The electric properties of HgTe nanowires thin film fabricated on glass substrates were investigated and showed Ohm contact.