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With an aim to explore the d0 ferromagnetism in Ag-doped ZnO compounds, the poly-crystalline samples of Zn 1 - x Ag x O (with 0 ≤ x ≤ 0.12) were synthesized by a standard solid-state synthesis technique. The XRD analyses indicated that these compounds have been formed as Ag:ZnO nanocomposite. According to scanning electron microstructural study, all compounds have a homogenous nearly spherical shape morphology. The EDS spectra reveal that the final produced compounds do not contain any unwanted external impurity. The magnetization versus field measurement at room temperature demonstrates that the undoped ZnO compound shows ferromagnetism embedded in diamagnetic matrix, whereas all Ag-doped ZnO samples exhibit a clear room temperature ferromagnetic behavior with coercivity values between 80 and 196 Oe. The maximum saturation magnetization was obtained for the Zn0.97Ag0.03O sample; however, it declines subsequently. The bound magnetic polarons (BMPs) has been considered to explain the observed ferromagnetic behavior. [ABSTRACT FROM AUTHOR]

Pure 2 based wide band gap semiconductors were prepared by mechanical alloying method by using steel and tungsten carbide vials. They were further annealed at 900°C. The XRD patterns could be refined by using P42/ space group with typical lattice parameters a = b = 4.7322 Å and c = 3.1848 Å. The as milled powders obtained from both the vials exhibit room temperature ferromagnetism (FM) without any transition element doping. However upon annealing, the FM was destroyed in one of the samples. The observed FM is explained in terms of oxygen vacancy and defects induced electrons and exchange interaction between them. The ferromagnetic transition temperature obtained from the temperature variation of magnetization was found to be 915 K. The initial magnetization data could be analyzed in terms of bound magnetic polaron model. The resonance field shift in electron spin resonance spectrum is explained in terms of observed ferromagnetism. [ABSTRACT FROM AUTHOR]

Abstract: Cerium-doped Y1− x Ce x MnO3 compounds have been prepared in single-phase form for x=0 to 0.10. X-ray diffraction (XRD) patterns could be analyzed by using P63cm space group. Temperature variations of ac susceptibility and magnetization measurements show that these Ce-doped materials exhibit weak ferromagnetic transition. The observed ferromagnetic transition is attributed to the double exchange ferromagnetic interaction between Mn2+ and Mn3+ ions due to electron doping. The M–H loops exhibit hysteresis along with linear contribution and were analyzed based on bound magnetic polaron (BMP) model. Increase in saturation magnetization and decrease in BMP concentrations have been observed with increase in Ce doping. [Copyright &y& Elsevier]

Abstract: The linear and nonlinear AC susceptibility as a function of temperature were measured on LaMn1− x Cu x O3 compounds for . Samples with exhibit paramagnetic to ferromagnetic transitions followed by low temperature spin glass like transition. The linear susceptibility exhibits strong frequency dependence and is analyzed in terms of standard theoretical model for spin glass. The magnitude and peak temperature of nonlinear susceptibility vary with AC field amplitudes. They are analyzed in terms of critical behaviour in the vicinity of spin glass transition temperature and the critical exponent is found to be 3.2. [Copyright &y& Elsevier]

Electron-doped Sr1-xLaxMnO3(0≤x≤0.50) and hole-doped (x=0.70 and 0.82) samples have been prepared by solid state route. X-ray diffraction patterns could be refined using P63 space group for x≤0.30 and $R\bar 3c$ space group for x≥0.40. Temperature variation of AC susceptibility measurements show that all the electron-doped materials exhibit paramagnetic to ferromagnetic transitions with the transition temperatures ranging from 375 to 393 K, followed by low temperature antiferromagnetic transitions. The ferromagnetic maximum susceptibility is found to increase systematically with La doping, i.e. with increase in Mn3+ ions. The high temperature resistivity data could be analyzed using the Mott-variable range hopping model. The hole-doped materials exhibit ferromagnetic to paramagnetic transition. [ABSTRACT FROM AUTHOR]

LaMn1-xCuxO3 compounds have been prepared in single phase form for x - 0 to 0.30. X-ray diffraction patterns recorded at room temperature could be mostly refined using Pbnm space group. Paramagnetic-to-ferromagnetic transitions have been observed up to x = 0.30, from ac susceptibility measurements. Metal-insulator transition in the vicinity of ferromagnetic transition temperature has been observed for x = 0.05 and the resistivity data in the metallic region could be explained in terms of electron-electron and electron-magnon scattering mechanisms. Further increase in Cu-doping beyond x = 0.05 leads to systematic decrease in ferromagnetic transition temperature and ultimately ferromagnetism is destroyed for x = 0.40. The resistivity data of all samples except x = 0.05 exhibit semiconducting behaviors and they could be mostly explained using the adiabatic small polaron hopping model. [ABSTRACT FROM AUTHOR]

La1−xCuxMnO3 compounds have been prepared in single phase form for x=0–0.20. X-ray diffraction (XRD) patterns were recorded at room temperature and these could be refined using R3¯c space group by employing rietveld method. The typical lattice parameters for x=0.10 sample are a=b=5.531 A˚ and c=13.352 A˚. dc electrical resistivity measurements were carried out below room temperature. The samples x≤0.10 exhibit metal–insulator transitions in the temperature range (TMI) 43–92 K. The resistivity data above TMI could be fitted to Mott variable range hopping (Mott-VRH) model. The samples x>0.10 could be mostly fitted to Efros–Shklovskii VRH (ES-VRH) model. Temperature variations of ac susceptibility down to 30 K were measured at an ac field amplitude of 5.3 Oe. All the above Cu doped samples exhibit paramagnetic to ferromagnetic transitions. [Copyright &y& Elsevier]

We report ferromagnetic behavior in undoped ZnO nanofibers prepared by electrospinning a solution of zinc acetate and poly vinyl alcohol followed by annealing at 550°C for about 90min. X-ray diffraction patterns of the heat treated as-spun composite fibers reveal the formation of ZnO nanowires in wurtzite structure with no noticeable impurity phases. ZnO nanowires annealed between 500°C and 600°C exhibited room temperature ferromagnetism with decreasing magnetization with increasing annealing temperature. Room temperature ferromagnetism was observed in as-spun fibers annealed in air as well as under vacuum. However, vacuum annealed nanofibers show higher magnetization as compared to air annealed fibers, which indicates that oxygen vacancy is a cause for the observed room temperature ferromagnetism in the ZnO nanofibers. [ABSTRACT FROM AUTHOR]

In the present research work, a conventional solid-state synthesis approach was used to synthesize the polycrystalline compound of Mg-doped ZnO (Zn 1-x Mg x O with x = 0–0.12). The XRD analysis reveals that Mg-doped compounds have been crystallized in a single hexagonal phase. The SEM analysis revealed that these compounds are constituted with microscopic spherical particles with a size range of 1–3 μm. Raman scattering spectra of these compounds displayed a blue-shift of the Raman active E 2 (low) mode attributed to the vibration of zinc atom in wurtzite ZnO, indicating Mg ions were substituted successfully into the ZnO lattice. Optical measurements revealed that the optical band gap enhanced from 3.12 to 3.17 eV, while the transmittance value improved from 87% to 96% as the Mg doping percentage is increased. The magnetization (M) versus applied field (H) measurements, done at 300 K reveals that the undoped ZnO compound exhibits weak ferromagnetic behavior, whereas all Mg-doped ZnO compounds show a strong ferromagnetism with coercivity ranging between 85 O e ≤ H c ≤ 1482 O e , and with the highest saturation magnetization of 0.255 emu/gm for 12% Mg-doped sample. [ABSTRACT FROM AUTHOR]

Abstract: The mixed valent manganites (La0.85Ag0.15)MnO3 with perovskite structure has been prepared by doping up to 50% of Co at the Mn site. Paramagnetic (PM) to ferromagnetic (FM) transitions have been observed in all the prepared materials. However, the long-range magnetic ordering observed in (La0.85Ag0.15)MnO3 is systemically reduced to cluster glass-type (short-range) of FM ordering due to the introduction of Co. The FM transition temperature was found to decrease with increase in Co doping up to 20% and for further increase in Co doping, the T c was found to increase. They are explained on the basis of competition between FM double exchange interactions in Mn–O–Mn and Co–O–Co networks. In addition to PM–FM transition, evidences of FM to antiferromagnetic (AFM), and AFM to reentrant spin-glass transitions have been observed. The shift in spin-glass freezing temperature, T f has been observed from the frequency variation of ac susceptibility measurements. The observed magnetic transitions are explained on the basis of magnetic interactions in different Mn–O–Mn, Mn–O–Co and Co–O–Co networks and such transitions are also observed from the measurement of third harmonic susceptibility. Metal–insulator transition and colossal magneto-resistivity have been observed up to 10% of Co doping. [Copyright &y& Elsevier]

Researchers have been making persistent efforts in recent years to find novel and suitable oxide materials with room temperature d0 ferromagnetic characteristics to be utilized in spintronics devices. The fundamental goal of this work is to investigate the effect of K/Mg co-doping on the structural, magnetic, optical, and transport (dielectric and Hall Effect) properties of Zn 0.94−y K 0.06 Mg y O compounds produced via solid-state process (y = 0, 0.02, 0.04, 0.06, 0.08). The X-ray diffraction pattern examination of these compounds revealed their hexagonal wurtzite structure. The Raman spectrum also displays the hexagonal wurtzite structure of ZnO without any lattice disorder. The elemental colour mapping demonstrates that all of the elements are dispersed uniformly throughout the compound. The concentration of K/Mg co-doping was increased, and this resulted in an improvement in the dielectric value and ac conductivity. Moreover, low dielectric loss in these compounds is observed and thus projecting it as a potential material to be utilized in high-frequency optoelectronic devices. The analyses of Nyquist plots show that higher Mg co-doping results in an increase of non-Debye kind relaxation and it led to a decrease in the grains and grain boundaries resistance. According to the analysis of dielectric data using the Maxwell-Wagner model, hopping of charge carriers are likely to be responsible for the electrical transport. As revealed from optical property measurement, the band gap was found to be slightly altered and the transmittance value increased from 82% for Zn 0.94 K 0.06 O to 86% for K/Mg co-doped ZnO compounds. The Hall Effect investigation clearly indicated p-type conductivity and enhanced carrier density concentration. Furthermore, it has been discovered that these substances exhibit ferromagnetism at room temperature. [Display omitted] • Zn 0.94 −y K 0.06 Mg y O compounds were synthesized by the solid-state reaction method. • Optical band-gap narrowing, p-type conductivity and carrier concentration enhancement was observed with the increase of Mg doping concentration. • The transmittance value increased from 82% for Zn 0.94 K 0.06 O to 86% for K/Mg co-doped ZnO compounds. • The dielectric constant and ac conductivity were found to increase with Mg-doping concentration. • Room temperature d 0 Ferromagnetism has been observed in all compounds. [ABSTRACT FROM AUTHOR]

Magnetic studies on aluminum-substituted cobalt ferrite nanoparticles (CoFeAl O ) of average particle size ∼20 nm in the broad range of temperature varying from room temperature (300 K) to 900 K has been presented. The temperature dependence of DC magnetization curve exhibits paramagnetic to ferrimagnetic transition at ∼736 K. Zero field cooling and field cooling magnetization measurement shows that the blocking temperature is far above the room temperature. The presence of ferrimagnetic order in the sample has been analyzed by Arrott plot technique for M-H data measured over the temperature range 300-900 K in the magnetic field of ±9 T. The magnetocrystalline anisotropy constant was determined by employing the 'law of approach (LA) to saturation' theory. The saturation magnetization, magnetocrystalline anisotropy constant and coercivity are found to decrease with the increase in temperature. [ABSTRACT FROM AUTHOR]

The Na-doped TiO 2 compounds, i.e Ti 1 − x Na x O 2 0 ≤ x ≤ 0.12 were synthesized via the solid-state synthesis method. The formation of single rutile phase with tetragonal structure was identified through the structural study by recording the XRD patterns. The analyses of the XRD patterns further indicate that Na+ ions are likely being substituted at the interstitial site of Ti4+ ions. The microstructural study using SEM revealed the homogeneous morphology of all compounds, with the particle size in the range of 1–2 μ m. The room temperature magnetization versus field measurement reveals a ferromagnetic behavior for all Na-doped compounds with coercivity values ranging from 100 to 930 Oe. The saturation magnetization was observed to be maximum for Ti 0.97 Na 0.03 O 2 compound but thereafter it decreases. According to optical property measurements, the bandgap reduces from 2.94 to 2.71 eV as the concentration of Na doping increases. The maximum transmittance value 91% was noted for Ti 0.97 Na 0.03 O 2 compound. The Hall effect measurements indicate that the carrier concentration of all Na-doped TiO 2 ranged from 1.077 × 10 15 to 7.579 × 10 15 /cm3, and it grew monotonically with the increase of Na-doping concentration. The value of the ac conductivity and dielectric constant were observed to enhance with increasing Na-doping concentration; indicating that transport occurs via hopping of the charge carrier. Further, the dielectric properties observation reveals lossless nature in the produced sample, which suggests that this material could be employed in high-frequency optoelectronic devices. [Display omitted] • Room temperature d 0 Ferromagnetism has been observed in Na-doped rutile TiO 2 compounds. • Hysteresis loops with a maximum saturation magnetization of 0.038 µ B per Na-ion was observed for 3% Na-doped compound. • Optical band-gap narrowing and carrier concentration enhancement was observed with the increase of Na doping concentration. • Very high optical transmittance value i.e., 83% (for TiO 2) to 91% (for 3% Na-doped TiO 2) was observed. • Zero dielectric loss was observed for all Na-doped compounds. • The dielectric constant and ac conductivity were found to increase with Na-doping. • These materials can be used for potential application for spintronics and optoelectronics devices. [ABSTRACT FROM AUTHOR]

The present work emphases on the structural, elemental, magnetic, optical, and electrical transport properties of Zn 1-x K x O (0 ≤ x ≤ 0.12) compounds for their plausible application in spintronic devices. These compounds have been crystallized in a single phase and formed with spherical particles of size 3–6 μm. At 300 K, the M − H curve reveals that undoped ZnO exhibits diamagnetism but all K-doped ZnO compounds show M − H hysteresis loops similar to ferromagnetic material with coercivity in the range of 80–140 Oe. These compounds exhibit maximum saturation magnetization of 0.04 μ B per K-ion for 6% K-doped compound. The optical band gap values of the prepared compounds are reduced as the K concentration increases. The value of transmittance was observed to enhance from 87% (for ZnO) to 92% (for 9% K-doped ZnO) sample. The Hall effect study reveals that all K-doped ZnO samples exhibit p-type nature and the carrier density (hole) increases with the increase of K concentration. [ABSTRACT FROM AUTHOR]

• Increase in M r , M S and H c with increase in BHF percentage BLFO-BHF composite. • ΔH ~ M plot explains the magnetic interaction between BLFO and BHF magnetic phase. • Vegard's law has been used to calculate the theoretical magnetization. • Law of approach to saturation has been employed to analyze the magnetic hysteresis. Two different sets of multiferroic nanocomposites i.e., (1-x)Bi 0.85 La 0.15 FeO 3 -(x)BaFe 12 O 19 with x = 0.00, 0.05, 0.10, 0.20, 0.30, 0.40, 0.50 and 1.00 have been synthesized by the solid-state reaction method and high energy planetary ball mill techniques. The peaks in the XRD patterns can be indexed to R3c crystal symmetry of Bi 0.85 La 0.15 FeO 3 and P63/mmc crystal symmetry of BaFe 12 O 19. It suggests the absence of any major chemical reaction between the two phases. Moreover, it is assumed thatBi 0.85 La 0.15 FeO 3 and BaFe 12 O 19 crystal symmetries are present in the composite independently. Magnetic properties have been improved significantly due to the incorporation of BaFe 12 O 19 in the composites. Vegard's law suggests that the experimentally observed magnetizations are higher than that of theoretically calculated value. The difference between the theoretical and experimental magnetization as well as the anomaly in the magnetic hysteresis have been explained by considering the magnetic interaction correlation length between Bi 0.85 La 0.15 FeO 3 and BaFe 12 O 19 magnetic phases. The hysteresis loop width (ΔH) versus M plots has been introduced to understand the magnetic interaction (exchange bias) between Bi 0.85 La 0.15 FeO 3 and BaFe 12 O 19. Magnetocrystalline anisotropy increases with the increase in the percentage of BaFe 12 O 19 in the composite. [ABSTRACT FROM AUTHOR]