Young-Eon Ihm

Effects of rapid thermal annealing on the ferromagnetic properties of sputtered Zn1−x(Co0.5Fe0.5)xO thin films

We have investigated the effects of rapid thermal annealing under vacuum on the CoFe-doped ZnO [Zn1−x(Co0.5Fe0.5)xO] films grown by reactive magnetron co-sputtering. At least up to x=0.15, the films have the single phase of the same wurtzite structure as pure ZnO. Ferromagnetism was observed for the CoFe-doped ZnO films. We found that rapid thermal annealing leads to a remarkable increase in the spontaneous magnetization of the CoFe-doped ZnO as well as the electron concentration. The annealing also leads to a significant increase in the Curie temperature (TC), resulting in room temperature ferromagnetism with TC>300 K for the CoFe-doped ZnO films.

Magnetotransport of p-type GaMnN assisted by highly conductive precipitates

GaMnN growth on GaAs (100) using a GaN single precursor via molecular beam epitaxy was undertaken. The grown layers revealed p-type conduction. It is confirmed that p-GaMnN reveals room temperature ferromagnetism with hysteresis loop having a coercivity of ∼100 Oe. The segregated phase showing a transition temperature of ∼200 K is assigned to Mn3GaN, and which enhances the conductivity of the surrounding GaMnN region. As a consequence, the GaMnN layer with segregation revealed an anomalous Hall effect at room temperature proving magnetotransport in GaMnN phase. The enhanced conductivity of GaMnN by the highly conductive second phase also revealed the importance of the role of the free carriers in the carrier-mediated ferromagnetism.

Enhanced carrier-mediated ferromagnetism in GaMnN by codoping of Mg

The effects of Mg codoping on the structural, electronic transport, and magnetic properties of GaMnN films are investigated. Mg was shown to compete with Mn for incorporation into the growing films at impingement, and to replace Mn. The partial replacement of Mn by Mg in GaMnN has resulted in an increase of conductivity of the region. The enhanced transport property due to the highly efficient dopant Mg resulted in a remarkable increase of the saturation magnetization, indicating an interaction between Mn and Mg for the carrier-mediated ferromagnetism. The increased carrier population by Mg codoping enabled a full mediation among the Mn atoms, and consequently, suppressed the paramagnetic rise in the temperature-dependent magnetization measurement.

Optimization of GaMnAs growth in low temperature molecular beam epitaxy

We present a detailed growth optimization procedure and experimental results for the growth of GaMnAs magnetic semiconductors in low-temperature molecular beam epitaxy. They were explored by using in-situ monitoring of the surface reconstruction patterns, double crystal/high-resolution x-ray diffraction, conductivity measurement, and superconducting quantum interference device measurements. The results showed strong correlations among the measurements. The room temperature conductivity measurement, in particular, was found to be a useful tool in forecasting the ferromagnetic transition temperature of the films. High quality GaMnAs films could contain Mn up to ≈5% without MnAs segregation at substrate temperatures of 215–275°C. The highest transition temperature of 80 K, however, was measured from the sample with 3.7% Mn grown at the substrate temperature of 250°C and As4 pressure of 1.4×10−6 torr for a growth rate of 0.25 μm/hr.

Improvement of magnetic property of GaMnN by codoping of Mg

GaMnN and Mg-codoped GaMnN films were grown in molecular beam epitaxy using a GaN single precursor. The structural, electrical, and magnetic properties were examined. The Mg-codoped GaMnN layers revealed room-temperature ferromagnetism. Codoping with Mg reduces the Mn incorporation, but increases the conductivity of the GaMnN films. At the same time, the saturation magnetization and coercivity have increased at room temperature. As this improvement was obtained with much reduced Mn concentration of ∼0.3%, the crucial role of the carriers for carrier-induced ferromagnetism in magnetic semiconductors is observed.

Annealing Effect on Magneto-transport Properties of Amorphous Ge 1-x Mn x Semiconductor Thin Films

Amorphous _ semiconductor thin films grown by low temperature vapor deposition were annealed at various temperatures from 400 to for 3 minutes in high vaccum chamber. The electrical and magnetotransport properties of as-grown and annealed samples have been studied. X-ray diffraction patterns analysis revealed that the samples still maintain amorphous state after annealling at for 3 minutes and they were crystallized when annealing temperature increase to . Temperature dependence of resistivity measurement implied that as-grown and annealed _ films have semiconductor characteristics, the increase of resistivity with annealling temperature was obseved. The -annealed sample exhibited negative magnetoresistance (MR) at low temperatures and the MR ratio was 8.5% at 10 K. The asymmetry was present in all MR curves. The anomalous Hall Effect was also observed at 250 K.

The Effects of Codoping of Be and Mg on Incorporation of Mn in GaAs

)Abstract Samples of GaMnAs, GaMnAs codoped with Be, and GaMnAs simultaneously codoped with Be andMg were grown via low-temperature molecular beam epitaxy (LT-MBE). Be codoping is shown to take the Gasites into the lattice efficiently and to increase the conductivity of GaMnAs. Additionally, it shifts thesemiconducting behavior of GaMnAs to metallic while the Mn concentration in the GaMnAs solid solution isreduced. However, with simultaneous codoping of GaMnAs with Be and Mg, the Mn concentration increasesdramatically several times over that in a GaMnAs sample alone. Mg and Be are shown to eject Mn from theGa sites to form MnAs and MnGa precipitates.Key wordsGaMnAs, Be codoping, Mg codoping, MBE, Magnetic semiconductor PACS: 75.50Pp, 75.70Ak, 81.15.Hi

Enhancement of Ferromagnetism in Laser-deposited (Zn,Mn) O Thin Films Codoped by Mg and P with p-type Conductivity

In the study, the authors reported on the appearance of room temperature ferromagnetism in (Zn,Mn)O codoped by Mg and P with p-type conduction. (Zn, Mn)O thin films codoped by Mg and P were grown on SiO2/Si substrates by using pulsed laser deposition (PLD) method from ceramic targets. Characterization of the films was done using X-ray diffraction and secondary ion mass spectrometry. Magnetic property measurements included the coexistence of ferromagnetic and paramagnetic components, magnetic hysteresis loop for the annealed film, and saturation magnetization.

Carrier-enhanced Ferromagnetism in Cr-doped ZnO

We have investigated the effects of Al codoping on the structural, electrical transport, and magnetic properties of oxide diluted magnetic semiconductor thin films prepared by reactive sputtering. Nondoped thin films show semiconducting transport behavior and weak ferromagnetic characteristic. The Al doping increases the carrier concentration and results in an decrease of resistivity and metal-insulator transition behavior. With increasing carrier concentration, the magnetic properties drastically change, exhibiting a remarkable increase of the saturation magnetization. These results show carrier-enhanced ferromagnetic order in Cr-doped ZnO.

Ferromagnetism and Magnetotransport of Be-codoped GaMnAs

Be-codoped GaMnAs layers were systematically grown via molecular beam epitaxy with varying Mn- and Be-flux. Mn flux was controlled to cover from solid solution type GaMnAs to precipitated GaMnAs. Two Be flux were chosen to exhibit semiconducting and metallic resistivity in the grown layers. The structural, electrical, and magnetic properties of GaAs:(Mn, Be) were investigated. The lightly Be-codoped GaMnAs layers showed ferromagnetism at room temperature, but did not reveal magnetotransport due to small magneto-resistance and high resistance of the matrix. However, room temperature magnetotransport could be observed in the degenerate Be-codoped GaMnAs layers, and which was assisted by the high conductivity of the matrix. The Be-codoping has promoted segregation of new ferromagnetic phase of MnGa as well as MnAs.ጊ缀Ѐ㘰〻Ԁ䭃䑎䷙᜙Ⴛ