S. Kazan

Size effects and origin of easy-axis in nickel nanowire arrays

High quality compact Ni nanowire (NW) arrays with aspect ratios (wire length/diameter) varying between 70–171 for a wire length of ∼6 μm, and between 3–400 for a constant wire diameter of 60 nm were successfully grown by direct current electrodeposition into free standing porous alumina templates having a lattice constant, i.e., interpore distance, of 105 nm. The NWs have been investigated using a combination of scanning- and transmission-electron microscopies, selected-area electron diffraction, x-ray diffraction analysis, ferromagnetic resonance (FMR), and vibration sample magnetometer techniques at room temperature. Microscopic and diffraction results show that the wires are uniform and mostly single-crystalline, being 220-oriented along the growth direction. Magnetic properties of samples are heavily dependent on the wire length as well as the diameter or packing factor, P (the volume fraction of wires/template). The FMR spectra and the field orientation dependence of the resonance field values were f...

Ferromagnetic resonance in double perovskite epitaxial thin films of La2NiMnO6 on SrTiO3 and NdGaO3 substrates

Ferromagnetic resonance (FMR) studies of epitaxial La2NiMnO6 (LNMO) thin films on (100) oriented SrTiO3 and (110) oriented NdGaO3 substrates at room temperature are presented. Observation of FMR spectra above the Curie temperature of this compound confirms the presence of magnetic ordering in LNMO thin films at room temperature. Best fitting of FMR spectra has been made on the assumption of the coexistence of two magnetic phases with different easy and hard axis periodicities in the film plane of LNMO. The spectra of the films on various substrates are characterized by different in-plane and out-of-plane symmetries, which indicates the existence of different epitaxial growth on the substrates with different crystal symmetries and orientations.

Sonochemical synthesis and chracterization of Mn3O4 nanoparticles

AbstractWe report on the synthesis of Mn3O4 nanoparticles (NPs) using a novel sonochemical method without requiring any pH adjustment. Synthesized material was identified as tetragonal hausmannite crystal structure model of Mn3O4 from XRD analysis. Crystallite size was estimated from x-ray line profile fitting to be 17±5 nm. FTIR analysis revealed stretching vibrations of metal ions in tetrahedral and octahedral coordination confirming the crystal structure. TEM analysis revealed a dominantly cubic morphology of NPs with an average size of ∼20 nm. Magnetic evaluation revealed a blocking temperature, TB of 40 K above which the material behaves paramagnetic. Asymmetric coercive field is attributed to the interaction between ferromagnetic Mn3O4 and antiferromagnetic Mn oxide at the surface of nanoparticles.

Electron Paramagnetic Resonance (EPR) Investigations of Iron-Doped Ferroelectric Ternary Thallium Chalcogenides

Abstract In this review article, we summarize the results of the first investigations of EPR spectra of iron-doped ternary thallium chalcogenides TlInS2, TlGaSe2, and TlGaS2 in a wide temperature interval including previously reported structural phase transitions. In these compounds, Fe ions substituted Ga and/or In sites in crystal structure and served as local probes to study ligand crystal field and its local symmetry around these paramagnetic sites. An overview of our recent EPR studies carried out at room temperature and in the temperature interval including structural phase transitions is provided. The results revealed the fine structure of EPR spectra of the paramagnetic Fe3 + ions and the local symmetry of crystal field (CF) at Fe3 + site and CF parameters. As a result of summarizing the low-temperature EPR investigations a discussion about active atomic groups, possible atomic displacements, and the local symmetry changes during the low-temperature phase transformations is presented.

Dielectric constant and EPR spectra of Fe doped TlInS2 crystal near the structural phase transitions

Dielectric constant and electron paramagnetic resonance (EPR) spectra of Fe-doped TlInS2 crystal has been investigated in the temperature range of 5–300 K. The influence of Fe impurities on dielectric properties of TlInS2 crystal has been considered in comparison with earlier observed results from pure TlInS2 compounds. Considerable decrease of the dielectric constant, as well as the change of the shape of its temperature dependence in a result of influence of doped iron atoms, has been observed. It has been established that EPR lines exhibit remarkable splitting and appearance of additional resonance lines at the temperatures lower than 200 K, which is attributed earlier as the temperature of the ferroelectric phase transition. The simulation for low-temperature EPR spectra has been performed taking into account the appearance of four additional centers in addition to four equivalent centers observed from EPR spectra at room temperature. Such transformations are considered as result of nonequivalent displacements of different groups of Tl atoms during the structural phase transitions.

Exchange bias in Pt doped NiMn thick films

Magnetization and electron spin resonance (ESR) measurements were carried out on a 1.2 at. % Pt doped NiMn thin film (8000 A) in the temperature range of 5–200 K for both parallel (field parallel to the film surface) and perpendicular configurations. M versus H loops were recorded at selected temperatures. Magnetization curves in the parallel configuration differ from those in the perpendicular geometry in many respects, including the anisotropy fields derived from these curves, and the coercivity. In addition, the temperature dependences of the magnetization in a small negative field (−0.5 Oe) and several larger positive fields will also be reported. All of these phenomena can be understood by the coexistence of Mn-rich and Mn-deficient aggregated granular regions coupled antiferromagnetically. Furthermore, the exchange stiffness constant (D), bulk anisotropy constant, and surface anisotropy constant were deduced from ESR measurements. The fitted ESR parameters are in good agreement with the behavior ded...

Ion beam synthesis and investigation of nanocomposite multiferroics based on barium titanate with 3d metal nanoparticles

Samples of nanocomposite multiferroics have been synthesized by implantation of Co+, Fe+, and Ni+ ions with an energy of 40 keV into ferroelectric barium titanate plates to doses in the range (0.5–1.5) × 1017 ions/cm2. It has been found that nanoparticles of metallic iron, cobalt, or nickel are formed in the barium titanate layer subjected to ion bombardment. With an increase in the implantation dose, the implanted samples sequentially exhibit superparamagnetic, soft magnetic, and, finally, strong ferromagnetic properties at room temperature. The average sizes of ion-synthesized 3d-metal nanoparticles vary in the range from 5 to 10 nm depending on the implantation dose. Investigation of the orientation dependence of the magnetic hysteresis loops has demonstrated that the samples show a uniaxial (“easy plane”) magnetic anisotropy typical of thin granular magnetic films. Ferromagnetic BaTiO3: 3d metal samples are characterized by a significant shift of the ferromagnetic resonance signal in an external electric field, as well as by a large (in magnitude) magnetodielectric effect at room temperature. These results indicate that there is a strong magnetoelectric coupling between the ferroelectric barium titanate matrix and ion-synthesized nanoparticles of magnetic metals.

Magnetisation dynamics of as quenched and pulse annealed soft metallic glasses

Abstract Pulse annealing method (PAM) is a practical and effective method to improve the magnetic characteristics of metallic glasses. Pulse annealing method overcomes oxidation problems during the annealing process. It minimises the difficulties in managing the crystallisation steps and causes low coercivity in contrast to high susceptibility in milliseconds. In this work, Fe77Cr2Si5B16 and Fe39Ni39Mo4Si6B12 metallic glasses were annealed by PAM. The ferromagnetic resonance spectra were measured, and the angular variation of resonance fields at the out of plane geometries was studied. The effective magnetisation and g factor fitting parameters were obtained as 3450 and 3750 Oe for Fe77Cr2Si5B16 and Fe39Ni39Mo4Si6B12 respectively from the angular variation of the resonance field. The M–H loops at room temperature were also plotted, and the changes of the magnetic properties were observed after pulse annealing. Amorphous to nanostructure steps can be seen from this method without any doubt.

FMR studies of half metallic ferromagnetic thin films Co2MnSn and Co2MnGe

Thin films of Heusler alloys Co2MnSn and Co2MnGe prepared on sapphire a-plane substrates by RF-sputtering have been investigated by ferromagnetic resonance (FMR) technique. The magnetic anisotropies of the Co2MnSn and Co2MnGe thin films have been probed and the effective magnetization values have been extracted. Weak in-plane anisotropies observed for the Co2MnGe sample indicate a textured growth of the films. Non-uniform (spin-wave and interface/surface) modes have been observed and the exchange stiffness constants for the Co2MnSn and Co2MnGe films have been estimated.