Vortex phase boundaries from ferromagnetic measurements in a patterned disc array

Using a recently developed broadband microwave measurement technique, we have studied the hysteretic appearance and disappearance with in-plane magnetic field of the uniform ferromagnetic resonance (FMR) mode of a patterned permalloy disk array. The observed features are consistent with our micromagnetic simulations (performed on an infinite array of such disk), which predict that on decreasing the magnetic field from a positively magnetized state at positive fields the array will: (i) pass continuously into a double-vortex state; (ii) followed by a discontinuous transition to a single-vortex state; and finally (iii) discontinuously into a negatively magnetized state at some negative field. The hysteretic counterpart occurs on reversing the field sweep and returning to positive fields. The FMR data are consistent with the hysteretic dc magnetization measurements performed earlier on samples patterned in an identical manner

A plausible method of preparing the ideal p-n junction interface of a thermoelectric material by surface doping

Recent advances in two-dimensional (2D) crystals make it possible to realize an ideal interface structure that is required for device applications. Specifically, a p-n junction made of 2D crystals is predicted to exhibit an atomically well-defined interface that will lead to high device performance. Using angle-resolved photoemission spectroscopy, a simple surface treatment was shown to allow the possible formation of such an interface. Ta adsorption on the surface of a p-doped SnSe shifts the valence band maximum towards higher binding energy due to the charge transfer from Ta to SnSe that is highly localized at the surface due to the layered structure of SnSe. As a result, the charge carriers of the surface are changed from holes of its bulk characteristics to electrons, while the bulk remains as a p-type semiconductor. This observation suggests that the well-defined interface of a p-n junction with an atomically thin {\it n}-region is formed between Ta-adsorbed surface and bulk.Comment: 4 figure

Vortex phase boundaries from ferromagnetic resonance measurements in a patterned disc array

Using a recently developed broadband microwave measurement technique, we have studied the hysteretic appearance and disappearance with in-plane magnetic field of the uniform ferromagnetic resonance (FMR) mode of a patterned permalloy disk array. The observed features are consistent with our micromagnetic simulations (performed on an infinite array of such disk), which predict that on decreasing the magnetic field from a positively magnetized state at positive fields the array will: (i) pass continuously into a double-vortex state; (ii) followed by a discontinuous transition to a single-vortex state; and finally (iii) discontinuously into a negatively magnetized state at some negative field. The hysteretic counterpart occurs on reversing the field sweep and returning to positive fields. The FMR data are consistent with the hysteretic dc magnetization measurements performed earlier on samples patterned in an identical manner

Temperature Dependence of the Band-Edge Photoluminescence of Mn-Doped ZnO Ceramics

We investigated of the near band-edge photoluminescence of the diluted magnetic semiconductor alloy Mn-doped ZnO. The near band-edge emissions of the excitonic transition were systematically investigated as a function of temperature. From the temperature dependence of the exciton peak, the Varshni temperature parameter, ??, was found to increase with increasing Mn. From the temperature dependence of the FWHM of the emission line, the broadening factors, (T), were determined from fits to the data. The activation energies of thermal quenching were obtained for both the D 0X and the A 0X peaks from the temperature dependence of the bound exciton peaks. Finally, we show that at high temperatures, the broadening of the FWHM is dominated by the LO phonon interaction.ope

Magnetic and electrical properties of new magnetic phase in Si1-xMnx crystals

We have investigated the magnetic and electrical transport properties of Si1-xMnx single crystals grown by the vertical Bridgman method. The alloys with Mn concentrations up to x=0.64 have weak ferromagnetic ordering around TC???30 K. However, Si0.25Mn0.75 alloys show weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, which is confirmed by magnetization and electrical transport studies.ope

Magneto-optical properties for bulk Cd0.63−yMn0.37HgyTe single crystals

We investigated the magneto-optical properties of diluted magnetic semiconductor Cd1-x-yMnxHgyTe (x similar to 0.37) single crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of y = 0.03). An anomalous behavior was also observed in the magnetic susceptibility and electrical resistivity. Faraday rotation as a function of photon energy with various Hg compositions for CdMnHgTe in the temperature range of 10-300 K has been measured. The Verdet dispersion curves were enhanced near the fundamental band gap energy. The Verdet constant becomes larger since the effect of the sp-d exchange interaction is enhanced as the temperature is lowered. At 10 K, the Verdet constants of the Faraday rotation for the samples with y=0, 0.01, 0.03, 0.05, and 0.07 were observed to be -1.09, -2.57, -3.94, -0.97, and -0.87 deg/G cm at 613 nm, respectively. The Verdet constant showed a maximum for the sample with y=0.03, and the value is approximately four times larger than that of the Cd0.63Mn0.37Te crystal. The Verdet constant has a maximum around Hg compositions with y similar to 0.03, and this result agrees well with the behavior of the magnetic susceptibility. This result reflects that Hg ion mediates and enhances the spin-spin interaction between Mn2+ ions with increasing Hg composition up to y similar to 0.03.ope

Structural, Electrical and Magnetic Properties of Diluted Magnetic Semiconductor Si1−xMnxTe1.5 Single Crystals

We studied the dependence of the magnetic properties on the Mn concentration of IV-VI diluted magnetic semiconductor Si$_{1-x}$Mn$_{x}$Te$_{1.5}$ single crystals prepared by using the vertical Bridgman technique. X-ray studies showed that the crystal structure was hexagonal. The magnetization measurement of Si$_{1-x}$Mn$_{x}$Te$_{1.5}$ showed a ferromagnetic ordering up to 80 K. With increasing Mn concentration, the saturation magnetization increased and the coercive field increased, as shown in the hysteresis loop. For $x$ = 0.20 and 0.31, a slope change in the resistivity was observed around 80 K and corresponded to a ferromagnetic (FM)-paramagnetic (PM) phase transition.ope

Magnetic, Structural, and Electrical Properties of Si1−xMnx Single Crystals

We have investigated the magnetic and the electrical transport properties of Si 1-xMn x (x = 0.5 and 0.75) single crystals grown by using the vertical Bridgman method. The alloys with the Mn concentration x = 0.5 have weak ferromagnetic ordering around T C ≃30 K. However, Si 0.25Mn 0.75 alloys show weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, which is confirmed by magnetization, electrical transport, and neutron diffraction studies. The conductivities appear to be n-type for samples with x = 0.5 and p-type for x = 0.75.ope