Papers by Keyword: Diluted Magnetic Semiconductor (DMS)

Abstract: The two-dimensional material MoS₂ has attracted a growing attention due to its potential applications in electronic devices in recent years [1,2,3], and the monolayer MoS₂ is a direct gap semiconductor with a band gap of 1.8eV [4]. In the existing studies, it has indicated that MoS₂ can get an available magnetism with doping transition metal atoms [5], and is expected to be a new generation of diluted magnetic semiconductor (DMS) [6,7]. Moreover, we found that Fe-doped MoS₂ could present a strong magnetism but a semimetal characteristic, losing its original semiconductor properties while obtaining magnetism. Therefore, it is necessary to explore some methods to make monolayer MoS₂ exhibit both magnetic and semiconductor properties. In this paper, we propose the method of N, Fe atoms co-doping to achieve this objective. The structural, electronic and magnetic properties of MoS₂ doped with transition metal Fe and VA atoms have been investigated by first principle calculations based on density functional theory. The 3×3×1 supercell of monolayer MoS₂ as a calculation model has been used. The result shows that pure MoS₂ has no magnetism, while Fe-doped MoS2 exhibits a good magnetism about 1.849μB but a semimetal characteristic. This is due to that Mo-4d, S-2p, Fe-3d states has a strong coupling around the Femi energy for the introduction of Fe atom, and the Femi energy only pass through the spin-up density of states. For the co-doping with VA atoms and Fe atoms, it is found that the magnetic moment of Fe-N, Fe-P and Fe-As co-doped MoS₂ is 0.956μB, 0.775μB, 0.782μB. Moreover, the Fe-N co-doped MoS₂ presents semiconductor characteristics, in contrast, Fe-P and Fe-As co-doped MoS₂ appear semimetal properties. It indicates that the semimetal characteristic of Fe-doped MoS₂ could change into indirect band gap semiconductor due to the introduction of N atom. The band gap is 0.2eV. Our study demonstrate that the method of Fe, N co-doping could make MoS₂ have good magnetic and also semiconductor properties at the same time.

Abstract: Ti_0.985Co_0.015O_2-δ thin films are deposited at 0, 0.1, 1 and 300 mTorr oxygen partial pressures by pulsed laser deposition (PLD) technique. Glancing angle x- ray diffraction (GAXRD) and micro-Raman spectroscopy show that the phase changes from rutile to anatase with increasing oxygen partial pressure. From Rutherford backscattering spectroscopic (RBS) technique, O to (Ti+Co) atomic ratio is found to increase with increasing oxygen partial pressure. Further, the simulation of RBS data while reveals non-uniform distribution of Co throughout the film deposited at 0 and 0.1 mTorr oxygen partial pressures, at 1 and 300 mTorr oxygen partial pressure, Co distribution is found to be uniform. Magnetic measurements confirm the room temperature ferromagnetism (RTFM) in all the films independent of the phase. Magnetic force microscopy (MFM) further supports the ferromagnetic nature of the films. We attribute the ferromagnetism in the films to be arisen from defects like oxygen vacancies rather than any contamination or Co clustering.

Abstract: Polycrystalline bulk sample Zn_0.99Fe_0.01O was fabricated by a solid-state reaction method and modified by high-pressure treatment technique at a pressure of 5GPa. The structure, morphology and magnetic properties of these samples were investigated in order to clarify the effect of pressure on magnetism of Zn-Fe-O system. It is found that the particle size of the modified samples becomes larger as well as the physical contact between neighboring particles becomes better. All samples show obvious ferromagnetic behaviors at room temperature, and the magnetization of modified samples greatly increases. It is believed that the larger particle size and the closer contact between neighbouring particles resulted from high-pressure treatment cause stronger ferromagnetic exchange interaction in Zn-Fe-O system.

Abstract: Co (t nm)/TiO₂ (200 nm) films were prepared by DC facing-target magnetron reactive sputtering system onto glass substrates at room temperature. The influence of the Co distribution on microstructure and magnetic properties of films was investigated in detail. The results indicate that CoTiO₂ thin films with t= 2 nm island-type deposited showed a homogeneous structure, and pure ferromagnetic properties of thin films are only attributed to the CoTiO₂ phases. On the other hand, in case of thin films above t= 2nm, the overall ferromagnetic properties depended on both CoTiO₂ and CoTi phases.

Abstract: The discovery of ferromagnetism (FM) in wide band-gap semiconductors doped with transition metals (TM), known as DMSs, has attracted much interest. Among DMSs, the system of Mn-doped ZnO is considered as the most promising candidates. This paper focuses primarily on the recent progress in the experimental studies of ZnO:Mn DMSs.

Abstract: Energy difference between the ferromagnetic and antiferromagnetic collinear orderings has been calculated for the uniform and dimer Mn-pair geometries in order to find the ground state distribution of the Mn atoms in InSb (As) hosts. We find the preference of the dimer ferromagnetic configuration of Mn dopants and an importance of optimizing the atomic site positions. The frequency-dependent optical and magneto-optical properties, namely the reflectivity, the electron energy loss spectra, on-and off-diagonal conductivity tensor and the polar Kerr effect, are calculated for comparison with available experimental data. Our calculated MO resonance in In_1-xMn_xSb (x=1.56%) are found to be in good agreement with corresponding experimental MO spectra. The origin of the large Kerr rotation is discussed.

Abstract: The galvanomagnetic properties in weak magnetic fields (4.2T300 K, B0.07 T) as well as Shubnikov-de Haas effect (T=4.2 K, B7 T) in the single crystal Pb_1-x-ySn_xV_yTe (x=0.20, y0.01) under hydrostatic compression up to 15 kbar have been investigated. It is shown that under pressure the decrease of activation energy of vanadium deep level, n-p-inversion of the conductivity type at low temperatures and insulator-metal transition take place. In the metallic phase sharp increase of the Hall mobility and appearance of Shubnikov-de Haas oscillations at helium temperature are observed. The pressure coefficient of vanadium level energy is determined and the diagram of the electronic structure rearrangement for Pb_1-x-ySn_xV_yTe under pressure is proposed.

Abstract: Temperature dependencies of the Seebeck coefficient, electrical conductivity, heat conductivity and the dimensionless thermoelectric figure of merit ZT of p-Bi₂Te₃, n-Bi₂Se₃ and Sb₂Te₃ doped by Fe or Cr have been investigated in the temperature interval 7 < T < 300 K. At T=4.2 K the Shubnikov-de Haas and Hall effects have been measured. By increasing the Fe content, the hole concentration decreases in p-Bi_2-xFe_xTe₃, while the electron concentration increases in n-Bi_2-xFe_xSe₃. The hole concentration decreases in Sb_2-xCr_xTe₃ with Cr doping. This demonstrates that Fe or Cr act as donors. The Seebeck coefficient increases in p-Bi_2-xFe_xTe₃ and Sb_2-xCr_xTe₃ with increasing Fe or Cr content, while it decreases in n-Bi_2-xFe_xSe₃.

Abstract: Magnetic properties of a GaAs-based heterostructures containing InGaAs quantum well and 2 nm thick GaAs layer doped with 5 at. % Mn (GaAs:Mn) on flat and vicinal substrates were studied. Two types of ferromagnetism were found. In the heterostructures grown on the flat substrate parallel to the (001) GaAs plane the magnetization obeys the Bloch T^3/2 temperature dependence while for the structures grown on the vicinal surface grown (disoriented by 3°) the magnetization follows percolation dependence.

Abstract: The magnetic susceptibility of Pb1-xCexX (X = S, Se and Te) crystals with several Cerium concentrations ranging from x = 0.006 to 0.036 has been measured between 2 K and 300 K. The experimental susceptibility curves were found to be consistent with a 2F5/2 lowest manifold for Ce3+ ions; the cubic crystal-field splitting values of 2F5/2 were estimated to be about 340 K, 440 K and 540 K for Pb1-xCexTe, Pb1-xCexSe, and Pb1-xCexS, respectively. For all the studied samples, it was found that the 7 doublet lies below the 8 quadruplet. These results confirm that Ce3+ ions substitute Pb2+ in the host crystals. Furthermore, the effective Landé factors were determined by X-band (~9.5 GHz) Electron Paramagnetic Measurements (EPR) to be g = 1.333, 1.364, and 1.402 for Ce ions in PbX, X = S, Se, and Te, respectively.