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Curie temperature of polycrystalline barium hexaferrite (BaFe12O19), prepared by conventional solid state technique, is anomalously and significantly enhanced (by nearly 15%) by energetic heavy ion irradiation (150 MeV, Ag12+) at ambient temperature due to dense electronic excitations Moderate fluence (1 × 1012 ions/cm2) induces structural defects giving rise to above enhancement. As established by X-ray diffraction, scanning electron microscopy and Raman studies, higher fluence (1 × 1013 ions/cm2) has structurally transformed the sample to amorphous phase with marginal change in magnetization and Curie temperature.

Electrical conduction behavior of ultrathin (5–110 nm) SnO2 films reactively sputtered at 150–400 °C substrate temperatures is presented. The surface roughness studies revealed that the films with lower thickness were smoother (≤0.6 nm). Stoichiometry/defect structure of the films obtained from X-ray photoelectron spectroscopy data and electron mobility are found to be dependent on film thickness and substrate temperature. The observed increase in conductivity of semi-metallic films with decrease in film thickness is attributed to changes in defect structure and surface roughness. Highest value of conductivity of about 715 Ω−1 cm−1 is obtained for 5 nm thick films deposited at 300 °C.

The charged state of bismuth atoms in n‐type bismuth‐modified amorphous thin films of Ge20Se80 and As2Se3 has been studied by x‐ray photoelectron spectroscopy. On the basis of the observed chemical shift, it is concluded that the Bi atoms in the modified films are positively charged. The charged Bi atoms perturb the equilibrium between positively and negatively charged defect centers, thereby causing a shift of the Fermi level towards the conduction band. The observed enhanced electrical conductivity and the conductivity conversion from p to n type in the modified films is the result of such a Fermi level shift.

The significant biaxial anisotropy contribution below 50 K is evidenced and identified as a cause of asymmetric “kinked” magnetization reversal behaviour and strong single cycle training effect in ion-beam sputtered IrMn/NiFe bilayers. The minor loop measurement clearly suggests that the magnetization reversal along the descending branch of the hysteresis loop takes place in two distinct steps comprising initial magnetization rotation followed by irreversible domain processes. Our experimental observations of characteristic magnetoresistance and minor loop measurements unambiguously endorse the recent theoretical prediction of Hoffmann suggesting the critical role of the symmetry of antiferromagnetic anisotropy on the reversal asymmetry and training effect.

Using magnetoresistance as a probe we demonstrate the correlation between reversal asymmetry and training effect in ion-beam sputtered IrMn/NiFe bilayers. During the training procedure, both exchange bias field and the degree of asymmetry decrease monotonically following a very similar trend. The analysis of the magnetoresistance behaviour establishes that the two distinct training mechanisms are operative. The first one is exhibited by an abrupt single cycle training effect and an accompanying pronounced reversal asymmetry, attributed to the presence of biaxial anisotropy in the IrMn layer. The second one displays a gradual cycling dependence due to thermal depinning of uncompensated antiferromagnetic spins.

The positive exchange bias (PEB) at room temperature in bottom pinned as-deposited IrMn(15 nm)/ CoFeB(10 nm) ion-beam sputtered bilayers is reported without any field cooling protocol. The necessary antiferromagnetic coupling of the interfacial spins and uniaxial exchange anisotropy in amorphous ferromagnetic CoFeB are caused by the energetic sputtered atoms that modify the local magnetic microstructure in situ. On magnetic annealing, enhancement in the coercivity and disappearance of PEB is observed due to the irreversible changes in the interfacial spin structure and CoFeB layer changing to ordered bcc (110).

In this work dc-magnetization, electronic structural, and Raman investigations of Ti1−xMnxO2 (x = 0.00, 0.05, 0.10, and 0.15) thin films deposited on fused-quartz substrate by a simple and cost effective spray pyrolysis technique have been reported. X-ray diffraction revealed the formation of pure anatase TiO2 phase devoid of elemental Mn clusters in all the Mn incorporated TiO2 films. It is established by x-ray photoelectron spectroscopic (XPS) measurements that Ti ions substituted by Mn ions in both divalent and trivalent states in the TiO2 matrix. No peak corresponding to Mn+4 could be evidenced by XPS. The Raman study has further established the formation of TiO2 in anatase structure in both pure TiO2 and Mn-doped TiO2 films. The Ti1−xMnxO2 films with x ≥ 0.05 exhibit ferromagnetic ordering at room temperature which arises most likely due to formation of bound magnetic polarons.

This paper presents a rapid and novel technique of growing nanowires of Si0.75Ge0.25 alloy at 900 °C in less than 10 min by processing the constituents in a TE011 single mode cylindrical resonant cavity, operated at 2.45 GHz and ∼300 W. The microstructural, crystal structural, and x-ray photoelectron spectroscopic studies of the nanowires have been carried out to establish their dimensions, crystallographic structure, and composition, respectively. It is proposed that the growth of nanowires is due to electromagnetic field assisted morphological transformation.

It has been possible to induce room temperature ferromagnetism, exhibiting high transition temperature, in tin oxide thin films by introducing manganese in a SnO2 lattice. The observed temperature dependence of the magnetization predicts a Curie temperature exceeding 550 K. A maximum saturation magnetic moment of 0.18±0.04 μB per Mn ion has been estimated for spray pyrolized Sn1−xMnxO2−δ thin films, with x=0.10. For Mn concentration (x) higher than 0.10, the films show linear behavior. The magnetization-versus-field studies indicate that the origin of ferromagnetism lies neither in ferromagnetic metal clusters nor in the presence of metastable phases. The structure factor calculations reveal that Mn has been incorporated in the SnO2 lattice. Also, the electron transport investigation indicates that there is a change of Mn occupancy from substitutional to interstitial sites of the SnO2 lattice when the Mn concentration exceeds 7.5 at. %. These films do not exhibit anomalous Hall effects at room temperature...

The high temperature magnetization behavior of an air sintered nanocrystalline ZnO:Co (5at.%) sample while it is subjected to thermal cycles in vacuum/air ambient is reported in the present paper. The pristine air sintered sample exhibits intrinsic room temperature ferromagnetism. Upon vacuum annealing, the magnetization of this sample increases significantly and the sample remains ferromagnetic up to 630°C. This has been attributed to the formation of Co clusters, and thus, the ferromagnetic ordering is extrinsic in nature. The subsequent air annealing of the vacuum annealed ZnO:Co (5at.%) sample, however, reverts back the magnetization to a value that was observed in the pristine air sintered sample. This is due to complete oxidation of the cobalt clusters. Furthermore, the sample’s magnetization at room temperature and also its temperature dependence up to 630°C remain unaffected by further annealing in vacuum or air, a feature required of a material for its device applications. The Curie temperature o...

High temperature magnetization studies (up to 650°C) of the chemically synthesized nanocrystalline Zn0.9Co0.1O samples are reported in this paper. A systematic study of sequentially sintered sample has been carried out to correlate the observed changes in magnetic behavior vis a vis very small changes in the unit-cell dimensions, evolution of cobalt oxide phases, and absence of Co clusters. The Curie temperature of cobalt substituted ZnO is determined to be ∼495°C. A plausible explanation of the observed room temperature ferromagnetism is presented in terms of bound magnetic polarons model.

A maximum room temperature ferromagnetic moment of 0.47μB∕Co ion has been observed in Sn0.9Co0.1O2−δ films grown by spray pyrolysis. The films have high conductivity (∼150Ω−1cm−1) and ∼70% transmittance in the visible region. A systematic variation of saturation magnetization, carrier concentration, electrical conductivity, and optical transmission edge in Sn1−xCoxO2−δ(0.05⩽x⩽0.15) films is correlated with the change in Co concentration, and a carrier mediated Ruderman-Kittel-Kasuya-Yoshida interaction has been proposed as the most probable mechanism for the ferromagnetic ordering. The maximum blueshift in the transmission edge by ∼215meV (at x=0.10) is attributed to the extra carriers generated by Co substitution.

Electrical, optical, and structural properties of hydrogenated amorphous germanium (a‐Ge:H) films prepared by reactive ion beam sputtering of a high‐purity crystalline germanium target under varying deposition conditions have been studied. A detailed description of the deposition setup, preparation procedures, and techniques of property measurement is given. The dependencies on beam voltage, H2:Ar flow ratio, and substrate temperature of the room‐temperature dark conductivity, optical band gap, hydrogen content, and ellipsometric and IR data are reported and analyzed. The minimum conductivity (10−4 Ω−1 cm−1) a‐Ge:H films have been obtained for H2:Ar flow ratio of 16:1, and beam voltage and substrate temperature of 1000 V and 250 °C, respectively. These films contain a hydrogen concentration of about 11 at. % and show an optical band gap near 1.04 eV. The IR spectra reveal absorption bands corresponding to both monohydride (Ge‐H) and dihydride (GeH2) groups for all the samples deposited. The monohydride ab...

Thin films of hydrogenated amorphous silicon‐germanium (a‐Si1−xGex: H) alloys have been prepared by reactive ion beam sputtering of a composite target of silicon and germanium. The dependence of the deposition rate, conductivity‐temperature variation, optical absorption coefficient, refractive index, imaginary part of the dielectric constant, hydrogen content, and infrared (IR) absorption spectra on germanium content (x) are reported and analyzed. For a typical composition—a‐Si28Ge72:H (x=0.72), the effect of beam voltage, H2:Ar flow ratio, and substrate temperature on the material properties have also been investigated. For the films prepared with increasing x, the expected behavior of a decrease in both hydrogen content and band gap and an increase in the electrical conductivity have been observed. The films prepared at x>0.80 are found to be more homogeneous than the films deposited at 0.0

Thin needles of ZnO have been grown at 480 °C, employing hydrous KOH melt as a solvent. Unlike other molten salt solvent methods, in the present case supersaturation is promoted by the decomposition of zincate ions. Laser Raman spectroscopic investigation made on molten hydrous KOH–ZnO system by employing a single—crystalline KCl cell has confirmed the presence of the zincate ion (ZnO22−) with a linear structure.

Room‐temperature studies of I‐V characteristics and variation of both the dielectric constant and dielectric loss with frequency are presented for ZnO‐Bi2O3 samples having different compositions and prepared by sintering at different temperatures. The nonlinearity parameter, dc resistivity, dielectric constant, and dielectric loss depend on the composition and sintering temperature. These parameters have been optimized for obtaining maximum nonlinearity and dielectric constant. The occurrence of a loss peak is, however, seen to be independent of the composition and sintering temperature. The present study, supported by a scanning electron microscope analysis, confirms the necessity of a two‐phase structure in the composite for its nonlinearity and high dielectric constant. The variation in the dielectric constant and nonlinearity parameter with sintering temperature for samples of different compositions has been explained on the basis of change in barrier height of Schottky barriers; the presence of these barriers has been inferred by the observed behavior of capacitance variation with bias.

Potential barriers responsible for nonlinear conduction in ZnO ceramic semiconductors (cersems) have been observed by both the intensity and Y‐modulation voltage contrast secondary electron microscopy techniques. The barriers exist at a grain‐intergranular interface and extend into the conducting ZnO grains. The applied voltage is distributed uniformly across the barriers. No electrical shorting of the barriers has been observed at fields exceeding the breakdown.

Zinc oxide whiskers, platelets, and dendrites have been grown on the ZnO substrate by a simplified and modified vapor phase technique which involves the production of zinc vapor at the growth temperatures itself. By this method, whiskers‐a few mm in length and a fraction of a mm in diameter‐have been obtained at growth temperatures ranging from 960 to 980°C. Change in growth habit from whiskers to platelets has also been observed. Various growth mechanisms have been discussed. It appears that the growth of these crystals takes place at supersaturations higher than those usually required for whisker growth. The dendrites have been observed to grow at about 930°C.

Binary ceramic semiconductor composites, prepared by sintering zinc oxide with barium oxide, exhibit nonohmic behavior owing to the presence of barium oxide. The nonlinearity parameter is strongly dependent on the composition and microstructure of the composite and has a maximum value of 50 for 10‐mol % BaO. At BaO concentrations of ⩾50 mol % the composite exhibits ohmic behavior due to the absence of a well‐defined two‐phase grain‐intergranular microstructure.