Magnetic studies on ZnTe:Cr film grown on glass substrate by thermal evaporation method

ZnTe and ZnTe:Cr films were prepared on glass substrate by using thermal evaporation method. X-ray diffraction analysis revealed the presence of ZnCrTe phase. X-ray photoelectron spectroscopy was used to estimate the composition of as-prepared films. The valence state of Cr in ZnTe:Cr film is determined to be +2 by using electron spin resonance spectroscopy. Magnetic moment data as a function of magnetic field was recorded by using superconducting quantum interference device magnetometry at 300 K. The result showed a clear hysteresis loop with coercive field of 48 Oe. Magnetic domains were observed by using magnetic force microscopy and the average value of domain size was 3.7 nm.     

Room-temperature ferromagnetism in Sn1−xMnxO2 nanocrystalline thin films prepared by ultrasonic spray pyrolysis

Sn_1−xMn_xO₂ (x=0.01-0.05) thin films were synthesized on quartz substrate using an inexpensive ultrasonic spray pyrolysis technique. The influence of doping concentration and substrate temperature on structural and magnetic properties of Sn_1−xMn_xO₂ thin films was systematically investigated. X-ray diffraction (XRD) studies of these films reflect that the Mn³⁺ ions have substituted Sn⁴⁺ ions without changing the tetragonal rutile structure of pure SnO₂. A linear increase in c-axis lattice constant has been observed with corresponding increase in Mn concentration. No impurity phase was detected in XRD patterns even after doping 5 at% of Mn. A systematic change in magnetic behavior from ferromagnetic to paramagnetic was observed with increase in substrate temperature from 500 to 700 °C for Sn_1−xMn_xO₂ (x=0.01) films. Magnetic studies reveal room-temperature ferromagnetism (RTFM) with 3.61×10⁻⁴ emu saturation magnetization and 92 Oe coercivity in case of Sn_1−xMn_xO₂ (x=0.01) films deposited at 500 °C. However, paramagnetic behavior was observed for the films deposited at a higher substrate temperature of 700 °C. The presence of room-temperature ferromagnetism in these films was observed to have an intrinsic origin and could be obtained by controlling the substrate temperature and Mn doping concentration.     

The structural and magnetic properties of Ni2Mn1−xBxGa Heusler alloys

The influence of the substitution of manganese by boron on the crystal structure and magnetic properties of Ni₂Mn_1−xB_xGa Heusler alloys with 0?x?0.5 has been investigated using X-ray diffraction, thermal expansion, resistivity, and magnetization measurements. The samples with concentrations x<0.25 were found to be of single phase and belonged to the cubic L2₁ crystal structure at room temperature. Crystal cell parameters of the alloys decreased from 5.830 to 5.825 Å with increasing boron concentration (x) from 0 to 0.25. The alloys were ferromagnetically ordered at 5 K and the saturation magnetization decreased with increasing boron concentration. The ferromagnetic ordering and structural transition temperatures for 0?x?0.3 have been observed and the phase (x−T) diagram of the Ni₂Mn_1−xB_xGa system was constructed. The phase (x−T) diagram indicates that the ground state of Ni₂Mn_1−xB_xGa alloys belongs to ferromagnetic martensitic, premartensitic, and austenitic phases in x?0.12, 0.12<x?0.18, and 0.18<x?0.3, respectively. The relative influence of cell parameters and electron concentrations on the phase diagram is discussed.     

Effect of sintering atmosphere on the electrical and optical properties of (ZnO)1−x(MnO2)x NTCR ceramics

Nominal composition of (ZnO)_1−x(MnO₂)_x (0.005≤x≤0.2) ceramics have been prepared by the standard solid-state reaction method in three different sintering atmospheres: Ar, air, and reductive atmosphere. The effect of sintering atmosphere on the electron spin resonance (ESR), negative temperature coefficient of resistivity (NTCR), and photoluminescence (PL) properties of (ZnO)_1−x(MnO₂)_x ceramics has been investigated in detail. The results demonstrate that the sintering atmosphere has significant effects on the ESR signals of (ZnO)_1−x(MnO₂)_x; the NTCR of the samples sintered in air is larger than those sintering in Ar and reductive atmosphere; the deep-level PL related to oxygen vacancy increases when sintered in the reductive atmosphere.     

Structure and magnetostriction of Tb0.2Pr0.8(Fe0.4Co0.6)1.93−xCx intermetallic compounds

The structure and magnetostriction of Tb_0.2Pr_0.8(Fe_0.4Co_0.6)_1.93−xC_x intermetallic compounds were studied by X-ray diffraction and magnetic measurements. Almost a single cubic Laves phase forms in the alloys for x ≤0.20, and a small amount of C can inhibit the formation of the 1:3 phase. The lattice parameter increases when 0≤x≤0.15, while the T_c and the spontaneous magnetization decreases with increasing x. The lattice parameter decreases slowly when 0.15≤x≤0.30, while the T_c decreases evidently with increasing x. The magnetostriction λ_a (=λ_∥-λ_⊥) is improved at low magnetic fields at room temperature for the compounds with 0.05≤x≤0.10, indicating that these C-containing compounds are promising magnetostrictive materials.     

Composition-dependent structural and electrical properties of PbSe1−xTex thin films

Polycrystalline PbSe_1−xTe_x ingots were prepared by solid-state microwave synthesis. Thin films of PbSe_1−xTe_x were then deposited onto clean glass substrates using vacuum evaporation technique. Their nanostructure morphologies and stoichiometric ratio were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectra (EDX). X-ray diffraction (XRD) patterns indicated that the lattice constants of PbSe_1−xTe_x powders and thin films increased with the increasing amount of Te. From the electrical property measurements, the thin films were characterized by n-type behavior.     

Spin-glass behavior of RNi1−xCuxAl compounds

The NdNi_1−xCu_xAl compounds were studied by means of heat-capacity, magnetization and AC-susceptibility measurements. The previously observed loss of long-range magnetic order in other RNi_1−xCu_xAl series with R=Tb, Dy, Er around x=0.6-0.8 that is accompanied by enhanced tendency to spin-glass character of behavior, is spread to wider concentration region of x=0.4-0.8 in the case of the newly studied Nd-based series, a candidate with rare-earth element coming from the light rare-earth group.     

Ferromagnetism in MnxGe1−x films prepared by magnetron sputtering

Mn_xGe_1−x thin films were prepared by magnetron sputtering with a substrate temperature of 673 K and subsequently annealed at 873 K. The X-ray diffraction (XRD) measurements showed that all samples had a single Ge cubic structure. No films showed clear magnetic domain structure under a magnetic force microscope (MFM). Atom force microscope (AFM) measurements showed that the films had an uniform particle size distribution, and a columnar growth pattern. X-ray photoelectron spectroscopy (XPS) measurements indicated that the valences of both Mn and Ge atoms increase with the Mn concentration. The resistance decreased with increasing temperature, suggesting that the films were typical semiconductors. Magnetic measurements carried out using a Physical Property Measurement System (PPMS) showed that all samples exhibited ferromagnetism at room temperature. There was a small concentration of Mn₁₁Ge₈ in the films, but the ferromagnetism was mainly induced by Mn substitution for Ge site.     

Luminescent properties of KGd1−x(WO4)2:Eux and KGd1−x(WO4)2−y(MoO4)y:Eux phosphors in UV-VUV regions

KGd_1−x(WO₄)_2−y(MoO₄)_y:Eu³⁺_x(0.1?x?0.75, y=0 and 0.2) phosphors are synthesized through traditional solid-state reaction and their luminescent properties in ultraviolet (UV) and vacuum ultraviolet (VUV) regions are investigated. Under 147 nm excitation, these phosphors show characteristic red emission with good color purity. In order to improve their emission intensity, the MoO₄²⁻ (20 wt%) is introduced into the anion of KGd_1−x(WO₄):Eu³⁺_x. The Mo⁶⁺ and Eu³⁺ co-doped KGd(WO₄)₂ phosphors show higher emission intensity in comparison with the singly Eu³⁺-doped KGd(WO₄)₂ in VUV region. The chromaticity coordination of KGd_0.45(WO₄):Eu³⁺_0.55 is (x=0.669, y=0.331), while that of KGd_0.45(WO₄)_1.8(MoO₄)_0.2:Eu³⁺_0.55 is (x=0.666, y=0.334) in VUV region.     

Abnormal positive thermal expansion in Mo substituted ZrW2O8

ZrW₂O₈ displays the unusual property of an isotropic bulk contraction in volume as a function of temperature. We report here on the positive thermal expansion (PTE) property caused by substituting Mo for W sites in ZrW₂O₈ at room temperature. The room temperature crystal structure of ZrW_2−xMo_xO₈ compounds, which were synthesized using a low temperature route, could be divided into ordered phase with α-ZrW₂O₈ structure (0≤x≤0.5) and disordered phase with β-ZrW₂O₈ (0.5<x≤1.5) and c-ZrMo₂O₈ structure (1.5<x≤2). ZrW_2−xMo_xO₈ adopting β-ZrW₂O₈ structure shows abnormal PTE property at room temperature due to the existence of water molecules, while ZrW_2−xMo_xO₈ adopting the other two structures (α-ZrW₂O₈ and c-ZrMo₂O₈) shows negative thermal expansion (NTE) property from room temperature until decomposition for α-ZrW₂O₈ structure or trigonal phase transition for c-ZrMo₂O₈ structure. The reason lies in the fact that the oxygen migration caused by the Mo substitution leads to the re-arrangement of W(Mo)O₄ tetrahedra lying along the 3-fold axis, only particular W/Mo ratio (0.5<x≤1.5) produces a special crystal structure, which allows the entrance of water molecules.     

Optical and physical properties of different composition of InxSe1−x thin films

Thin film binary alloys of In_xSe_1−x (0.05?x?0.30) have been prepared by the thermal evaporation technique. The optical transmission and reflection spectrum of these films were measured in the range 300-1100 nm. Both refractive index, n and extinction coefficient k have been determined from transmission and reflection measurements in terms of Murmann's equations. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. The width of band tail is determined and the optical absorption edge is described using the ‘non-direct transition’ model proposed by Tauc. Finally, the relationship between the optical gap and chemical composition in In_xSe_1−x amorphous system is discussed in terms of the average heat of atomization H_s and average coordination number N_c. The results of these calculations can be used rationalize the observed optical properties of these materials. Finally, the chemical bond approach has been also applied to interpret the decrease of the glass optical gap with increasing In content.     

Effect of Cr substitution on the multiferroic properties of BiFe1 − xCrxO3 compounds

Single-phase BiFe_1 − xCr_xO₃ (x=0, 0.05 and 0.1) compounds are synthesized by a sol-gel process. The lattice parameters decrease and the magnetizations increase with the Cr content. Moreover, the magnetoelectric coupling between magnetic order and ferroelectric order at room temperature was enhanced.     

Optoelectronic properties of Cu1−xPtxFeO2 (0 ≤ x ≤ 0.05) delafossite for p-type transparent conducting oxide

The samples of Cu_1−xPt_xFeO₂ (0 ≤ x ≤ 0.05) delafossite have been synthesized by solid-state reaction method to investigate their optical and electrical properties. The properties of electrical resistivity and Seebeck coefficient were measured in the high temperature ranging from 300 to 960 K, and the Hall effect and the optical properties were measured at room temperature. The obtained results of Seebeck showed the samples are p-type conductor. The optical properties at room temperature exhibited the samples are transparent visible light material with optical direct gap 3.45 eV. The low electrical resistivity, hole mobility and carrier density at room temperature displayed value ranging from 0.29 to 0.08 Ω cm, 1.8 to 8.6 cm²/V s and 1.56 × 10¹⁸ to 4.04 × 10¹⁹ cm⁻³, respectively. The temperature range for transparent visible light is below 820 K because the direct energy gap contains value above 3.1 eV. Consequently, the Cu_1−xPt_xFeO₂ delafossite enhance performance for materials of p-type transparent conducting oxide (TCO) with low electrical resistivity.     

Luminescence investigation of red phosphors Ca0.54Sr0.34−1.5xEu0.08Smx(MoO4)y (WO4)1−y for UV-white LED device

Ca_0.54Sr_0.34−1.5xEu_0.08Sm_x(MoO₄)_y (WO₄)_1−y red phosphors were prepared by solid-state reaction using Na⁺ as a charge compensator for light-emitting diodes (LED). The effects of Na⁺ concentration, synthesis temperature, reaction time and Eu³⁺ concentration were studied for the properties of luminescence and crystal structure of red phosphors. The results show that the optimum reaction condition is 6%, 900 °C, 2 h and 8%. The photoluminescence spectra show that red phosphors are effectively excited at 616 nm by 292, 395 and 465 nm. The wavelengths of 465 nm nicely match the widely applied emission wavelengths of blue LED chips.     

Cr-doping effect on the structural, magnetic, transport properties and Raman spectroscopy of La(2+x)/3Sr(1−x)/3Mn1−xCrxO3 perovskites

A series of the double-doping samples La_(2+x)/3Sr_(1−4x)/3Mn_1−xCr_xO₃ (0?x?0.25) with the Mn³⁺/Mn⁴⁺ ratio fixed at 2:1 have been fabricated. The structural, magnetic, transport properties and Raman spectroscopy have been investigated, and no apparent crystal structure change is introduced by Cr doping up to x=0.25. But the Curie temperature T_C and metal-insulator transition temperature T_MI are strongly affected by Cr substitution. The room temperature Raman spectra start exhibiting some new features following the increasing concentration of Cr substitutions. Moreover, it is worth noting that the frequency of the A_1g phonon mode can also be well correlated with the A-site mismatch effect (σ²), which is influenced mainly by the variety of the Sr content.     

Ferromagnetism in Zn1−xCrxTe (x = 0.05, 0.15) films grown on GaAs(1 0 0) substrate

Zn_1−xCr_xTe (x = 0.05, 0.15) films were grown on GaAs(1 0 0) substrate by thermal evaporation method. X-ray diffraction analysis showed the presence of ZnCrTe phase without any secondary phase. The surface was analyzed by high resolution magnetic force microscope and profile measurements showed orientation of magnetic domains in the range of 0.5–2 nm with increase of Cr content. Magnetic moment–magnetic field measurements showed a characteristic hysteresis loop even at room temperature. The Curie temperature was estimated to be greater than 300 K. From the electron spin resonance spectra, the valence state of Cr in ZnTe was found to be +2 with d² electronic configuration. Hall effect study was done at room temperature and the result showed the presence of p-type charge carriers and hole concentration was found to increase from 5.95 × 10¹² to 6.7 × 10¹² m⁻³ when Cr content increases. We deduce the origin of ferromagnetic behavior based on the observed experimental results.     

Nanoscale semiconductor Pb1−xSnxSe (x = 0.2) thin films synthesized by electrochemical atomic layer deposition

In this paper the fabrication and characterization of IV-VI semiconductor Pb_1−xSn_xSe (x = 0.2) thin films on gold substrate by electrochemical atomic layer deposition (EC-ALD) method at room temperature are reported. Cyclic voltammetry (CV) is used to determine approximate deposition potentials for each element. The amperometric I-t technique is used to fabricate the semiconductor alloy. The elements are deposited in the following sequence: (Se/Pb/Se/Pb/Se/Pb/Se/Pb/Se/Sn …), each period is formed using four ALD cycles of PbSe followed by one cycle of SnSe. Then the deposition manner above is cyclic repeated till a satisfactory film with expected thickness of Pb_1−xSn_xSe is obtained. The morphology of the deposit is observed by field emission scanning electron microscopy (FE-SEM). X-ray diffraction (XRD) pattern is used to study its crystalline structure; X-ray photoelectron spectroscopy (XPS) of the deposit indicates an approximate ratio 1.0:0.8:0.2 of Se, Pb and Sn, as the expected stoichiometry for the deposit. Open-circuit potential (OCP) studies indicate a good p-type property, and the good optical activity makes it suitable for fabricating a photoelectric switch.     

Magnetic and magneto-transport properties of double perovskite Ba2−xSrxFeMoO6 system

The structural magnetic and magneto-transport properties of double perovskite system Ba_2−xSr_xFeMoO₆ (0?x?1.0) prepared in bulk polycrystalline form are reported in this paper. X-ray diffraction analysis showed that samples are single phase and the lattice constants decreases with increase in the Sr content. The degree of Fe-Mo ordering has been found decreasing in the series with an increase in the Sr content. Parent compound Ba₂FeMoO₆ exhibits saturation magnetic moment value of 3.54 μ_B/f.u. at 85 K in a magnetic field of 6000 Oe. Temperature dependence of resistivity shows metallic behavior for all the samples. The magneto-resistance (MR) of the compound with x=0.4 is higher than that of the other samples. At room temperature this system shows a saturation magnetization value of 1.73 μ_B/f.u. and MR value of 7.08% (1 T). The observed variations in the structural and magnetic properties are attributed to the change of chemical pressure due to the substitution of Sr in place of Ba. The effect of antisite disorder (ASD) defects on magneto-transport properties is studied in more detail.     

Influence of low Co substitution on magnetoelastic properties of HoFe11Ti intermetallic compound

The thermal expansion and magnetostriction of HoFe_11−xCo_xTi (x=0, 0.3, 0.7 and 1) intermetallic compounds were measured, using the strain gauge method in the temperature range 77–590 K under applied magnetic fields up to 1.5 T. Results show that for samples with x=0 and 0.3, both linear thermal expansion and linear thermal expansion coefficient exhibit anomalies below the Curie temperature. Below room temperature, the spontaneous volume magnetostriction decreases with Co content. For all compounds studied, the anisotropic magnetostriction shows similar behaviour in the measured temperature range. The magnetostriction compensation occurs above room temperature in all samples. The volume magnetostriction shows a linear dependence on the applied field and by approaching the Curie temperature this trend changes to parastrictive behaviour. The results of the spontaneous magnetostriction are discussed based on the local magnetic moment model. The contribution of magnetostriction attributed to the magnetic sublattices R and T (Fe or Co) is discussed.     

Structural and electrical characterization of SxSe100−x thin films

Thin films of samples of the glassy S_xSe_100−x system with 0 ≤ x ≤ 7.28 have been prepared by thermal evaporation technique at room temperature (300 K). X-ray investigations show that the structure of pure selenium (Se) does change seriously by the addition of small amount of sulphur S ≤7.28%. The lattice parameters were determined as a function of sulphur content. Results of differential thermal analysis (DTA) of the glassy compositions of the system S_xSe_100−x were discussed. The characteristic temperatures (T_g, T_c and T_m) were evaluated. Dark electrical resistivities, ρ, of S_xSe_100−x thin films with different thicknesses from 100 to 500 nm, were measured in the temperature range from 300 to 423 K. Two distinct linear parts with different activation energies were observed. The variation of electrical resistivity of examined compositions has been discussed as a function of the film thickness, temperature and the sulphur content. The application of Mott model for the phonon assisted hopping of small polarons gave the same two activation energies obtained from the resistivity temperature calculations.