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We report the chemical synthesis of Cr-doped ZnS nanocrystallites without using any capping ligand/surfactant. An unusual increase in bandgap observed for Cr-doped samples was understood in terms of the Burstein–Moss effect. Additionally, 4A2(F) → 4T1(F) and 4A2(F) → 4T2(F) transitions in the absorption spectra confirmed the substitution of Cr3+ ions at the octahedrally coordinated interstitial sites. Photoluminescence study showed a large amount of Zn vacancies owing to the incorporation of Cr3+ ions which intensified the self-activated blue–green luminescence. Room-temperature magnetization showed FM ordering up to the 2% Cr doping, which gradually transformed into paramagnetic behavior at higher values and became more enhanced in the low-temperature range. Thus, in the present synthesis method, the FM order could only be observed up to the 2% Cr doping concentration. Also, the activation energy was observed to increase with the increase of Cr doping concentration. [ABSTRACT FROM AUTHOR]

Diluted magnetic semiconductors (DMSs), having interesting magnetic/transport properties, are currently being explored in photocatalytic application as well. This report presents photocatalytic and low temperature magnetic/transport study of chemically synthesized 3-5 nm sized cubic Zn1-xCuxS (0 ≤ x ≤ 0.04) DMS nanoparticles. Both studies have their own importance, former relates to dye degradation, while later attempts to understand origin of magnetic behavior in DMSs (which is still debatable). As a photocatalyst, Cu doped ZnS NPs showed enhanced degradation-efficiency for methylene blue dye. Magnetization study showed enhanced magnetic moment in Cu doped samples, which in the low temperature regime got further enhanced and was understood due to defect induced ferromagnetism. Low temperature transport study showed the decrease in resistivity of the Cu doped samples and was understood in terms of defects states created due to doping of the Cu ions and governed by conduction mechanism, namely thermal activation and variable range hopping. [ABSTRACT FROM AUTHOR]

We present the relationships between the structure, magnetic properties and high-frequency magnetoresistance (MR) effect in melt-extracted CoFeBSi microwires subject to thermal annealing. In order to release residual stresses to improve the magnetic softness while retaining the good mechanical property of an amorphous material, microwire samples were annealed at different temperatures of 100°C, 200°C, 350°C, 400°C, and 450°C for 15 min. We have shown that relative to an as-cast amorphous microwire, annealing microwires at T = 100°C, 200°C, and 350°C improved both the magnetic softness and the MR effect, while an opposite trend was observed for the microwires annealed at T = 400°C and 450°C. We have observed a distinct difference in the frequency dependence of MR response ( ξ) for dc applied magnetic fields below and above the effective anisotropy field of the microwires. While the microwire annealed at 200°C shows the largest MR ratio (~580%) at 100 MHz, the highest value of ξ (~34%/Oe) has been achieved at 400 MHz for the microwire annealed at 350°C. These results indicate that the optimally annealed CoFeBSi microwires are attractive candidates for high-frequency sensor applications. [ABSTRACT FROM AUTHOR]

The thermoelectric properties of n-type HgCdTe (MCT) and of MCT layers with n-p structure have been investigated in transverse (B ⊥ ∇T) and longitudinal (B |∇T) magnetic fields (0 ≤ B ≤ 16 kG) using the lateral gradient method at temperatures between 10 and 300K. The experimental results were analyzed by considering the contributions of electrons and holes to the magneto-thermoelectric effect and the scattering mechanisms involved. The analysis is based on a nonparabolic conduction band and Landau quantization as well as empirical relations for the band gap, the intrinsic carrier density, and the magnetoresistance. For n-type MCT at low temperatures (10 < T < 30K) and weak magnetic fields (B < 2 kG), the transverse magneto-thermoelectric effect (TME) was seen to be dominated by electron scattering on ionized defects. Longitudinal acoustic phonon drag was found to affect the TME in strong magnetic fields (B > 3 kG) at low temperatures (T < 20K). Longitudinal (LO) phonons were shown to prevail in the electron scattering at higher temperatures (T > 50K) in weak magnetic fields. With increasing magnetic fields, the effect of LO-phonon scattering decreases, and eventually the TME becomes independent of electron scattering. The longitudinal magneto-thermoelectric effect of n-type MCT was also found to exhibit magnetophonon oscillations due to LO-phonon scattering from both HgTe and CdTe phonons. The transverse magnetoresistance (TMR) of the n-type layers in the quantum region has been found to be linearly dependent on the magnetic field. Owing to the TMR of the n-type layers, the variation of the TME of p-n multiple layers with magnetic field is much larger than the variation of the Seebeck coefficient with temperature. Thus, the sensitivity to p-type layers is considerably enhanced compared to that of the Seebeck coefficient. As a result, the TME has proved to be particularly useful in determining the doping and composition of the constituent layers of MCT n-p structures. [ABSTRACT FROM AUTHOR]