Takeshi Kawagoe

Abstract We investigate the surface morphology and magnetic properties of 6-nm-thick Cr films prepared by first depositing a 2-nm-thick Cr layer at 290 K, followed by an additional 4-nm-thick layer deposited at 570, 620, and 670 K. Magnetic images of these Cr films, together with their topographic images, are obtained at 290 K via spin-polarized scanning tunneling microscopy. Our results show that surface morphology and magnetism of the Cr films depend significantly on the growth temperatures due to increasing screw dislocation density. Distinct magnetic contrasts featuring a layered antiferromagnetic (LAF) order are observed in the films grown at 570 and 620 K; however, different types of spin frustrations are observed. Two equivalent domains of the LAF order in the 〈100〉 direction are formed in the films grown at 620 and 670 K, which dissolve complex spin frustration. These findings may be important to advance spin electronics using AF films.

Abstract We investigate the room-temperature growth of ultrathin Mn films on Au(001) surface for Mn thicknesses (dMn) up to 1.5 nm. The surface structure and morphology at various dMn are investigated via scanning tunneling microscopy and low-energy electron diffraction (LEED). Although the formation of surface Au-Mn alloy is observed at dMn = 0.3 nm, body centered-tetragonal (bct) Mn(001) films grow epitaxially in a layer-by-layer mode at dMn = 0.6 and 1.0 nm, showing a p(1×1) LEED pattern with the in-plane lattice constant of Au(001). The surface morphology comprises primarily atomically flat terraces with spiral growth patterns at dMn = 1.0 nm. At dMn = 1.5 nm, three-dimensional islands are observed, thus indicating growth-mode change from layer-by-layer to layer-plus-island. The differential-conductance spectrum for dMn = 1.0 nm shows distinct peaks at -0.07 and -0.45 V, which may correspond to the spin-polarized surface states of the bct Mn(001) film surface.

Abstract We investigate the growth of ultrathin Cr films on a Au(001) surface and observe that the growth of 1.5 nm thick Cr layers at 290 K, followed by post-annealing at 520 K, results in high-quality epitaxial Cr(001) films with atomically flat large terraces and distinct surface states. Subsequently, these optimized growth conditions are successfully applied to the growth of 1 nm and 3 nm thick Cr films. Magnetic imaging of 1 and 1.5 nm thick Cr(001) films prepared under the optimized growth conditions is performed using spin-polarized scanning tunneling microscopy. Distinct magnetic contrasts featuring a topological antiferromagnetic (TAF) order are observed in both films; however, spin frustration originating from the density of screw dislocations for both films shows a significant difference. The 1.0 nm thick Cr film, which exhibits a clear TAF order with the suppression of a large spin-frustrated area, is suitable for application to spin-electronic devices.

Abstract We investigated the growth and surface morphology of 10 monolayer (ML)-thick Cr(001) films on clean Au(001) surfaces. High quality epitaxial Cr(001) films with large atomically flat terraces and distinct surface states were successfully fabricated through growth at 300 K and subsequent post-annealing at 520 K. At 300 K, spin-polarized scanning tunneling microscopy images of both the topological and magnetic structures of this Cr film were obtained. The magnetic images exhibited the following features: (1) The layered antiferromagnetic (AF) order appeared in adjacent terraces and one ML-depth shallow hole in the terraces; (2) significant spin frustrations induced by adjacent paired screw dislocations caused the AF domain formation with 90 degrees quantum axis rotation and a large spin frustration area, not always limited in the vicinity of screw dislocations. The feature (2) was qualitatively reproduced by the micromagnetic simulation. These findings may be essential for the further development of spin-electronics utilizing thin AF films.