M. Ikram

Effect of Mn doping on structural, morphological and dielectric properties of EuFeO3 ceramics

Polycrystalline compounds of EuFe1−xMnxO3 (x = 0.0, 0.3, 0.5) were synthesized by a standard solid state reaction technique. These compounds were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM) and dielectric properties. The Rietveld analysis of the XRD profiles clearly indicated that these compounds are well fitted with an orthorhombic structure and space group Pbnm. Raman spectral features revealed their fingerprint modes and irreducible representations at the Brillouin zone center as per the group theory. The surface morphologies from SEM images revealed that the average grain size increases with Mn doping. Energy dispersive X-ray analysis indicated the presence of Eu, Fe, Mn and oxygen. The dielectric properties were studied as a function of frequency and temperature. Absence of any loss peak in the dielectric dispersion suggests its behaviour to be that of a quasi-dc-process (QDC). The increase of dielectric constant with Mn doping suggests that small polarons contribute to the conduction mechanism.

Structural Analysis and Dielectric Properties of HoFe 1− x Ni x O 3 (0 ≤ x ≤ 0.5)

Bulk samples of HoFe1−xNixO3 (x = 0, 0.1, 0.3, 0.5) were synthesized through the conventional solid-state reaction route and subjected to various structural and electrical characterization techniques. The x-ray diffraction patterns confirm that the samples exist in a single phase with orthorhombic structure having space group Pbnm. With increasing Ni content, the unit cell volume and lattice parameters undergo small variation, as further confirmed by Raman spectroscopy measurements, especially towards higher wavenumber. Dielectric loss and permittivity measurements were performed at varying temperature and frequency. The permittivity increases with Ni doping. Further, the permittivity and dielectric loss exhibited different behavior with temperature and frequency variation. The alternating-current conductivity results show a small-polaron-type contribution in the conduction mechanism of these orthoferrites.

Investigating spin reversal and other anomalies in magnetic, transport and specific heat measurements of NdFeO3 and NdFe0.5Ni0.5O3 ortho-perovskites

Polycrystalline NdFeO3 (NFO) and NdFe0.5Ni0.5O3 (NFNO) compounds were synthesized by the standard solid state reaction route and were characterized to understand their structural, electrical, magnetic and thermal properties, and electronic structure. Rietveld refinements of the X-ray diffraction pattern confirm the single phase nature of both these compounds with an orthorhombic structure having the space group Pbnm. The temperature dependent resistivity follows the variable range hopping (VRH) model. From this model, the parameters such as density of states (DOS) at the Fermi level N(EF), hopping distance Rh, hopping energy Eh etc. were calculated. Electrical, magnetic and specific heat [Cp(T)] properties of the NFO and NFNO compounds were systematically studied in the temperature range of 2 to 300 K to understand the spin reorientation transition, magnetic intersection and magnetic inversion anomalies. NFO and NFNO exhibit an interesting phenomenon of spin reversal at low temperatures. The magnetic behaviour at low temperatures and fields is explained based on the competition among magnetic moments of rare earth (Nd) and transition metal ions (Fe/Ni). At a low magnetic field (500 Oe), the zero field cooled (ZFC) and field cooled (FC) branches intersect at low temperatures TX of 8.75 K and 17.05 K for NFO, and NFNO respectively. Below TX, the magnetization is negative. The FC curve crosses the M = 0 axis at 4.7 K for NFO, and 5.2 K for NFNO. The spin reorientation transitions are observed in the temperature range of 100–200 K for NFO and NFNO samples with a transition of the Fe3+/Ni3+ magnetic moments from Γ4(Gx,Fz)-type ordering (at high temperatures) to Γ2(Gz,Fx)-type ordering (at low temperatures). The isothermal hysteresis loops show a decrease of magnetization and increase of coercivity with the temperature and complements the magnetization versus temperature data. The Schottky and crossing point anomalies and the effect of an applied magnetic field over them at low temperatures of these compounds were also investigated. In addition to the above properties and magnetic and the thermal anomalies of NFO and NFNO instigated by the spin reorientation were also discussed.

Effect of Ni doping on optical, electrical and magnetic properties of Nd orthoferrite

NdFe1−xNixO3 (NFNO) (x=0.0 and 0.3) perovskite structures were synthesized by ceramic method. The variation of dielectric behavior with frequency at room temperature reveals an order of enhancement in both dielectric constant and dielectric loss with 30 percent Ni substitution. UV-Visible spectroscopy data exhibit that optical energy band gap decreases with Ni substitution from 4.3eV to 4.0eV for the sample with 30% Ni doping. Magnetic disorder over some range between 1.5K and 100K is observed in SFNO samples and is explained in milieu of interaction among Nd and Fe/Ni sub-lattice moments.

Ion-beam-induced ferromagnetism in Ca-doped LaMnO3 thin films grown on Si (100)

ABSTRACT The ion-bean-induced room temperature ferromagnetic ordering in pulsed laser deposited Ca-doped LaMnO3 thin films grown on Si (100) are presented in the present study. In addition to this, changes bought by the ion beam in structural, morphological and electrical properties are presented. Dense electronic excitation produced by high energy 120 MeV Ag9+ ion irradiation causes change in surface roughness, crystallinity and strain. It is also evident that these excitations induce the magnetic ordering in this system. The observed modifications are due to the large electronic energy deposited by swift heavy ion irradiation. The appearance of ferromagnetism at 300 K in these samples after irradiation may be attributed to the canting of the antiferromagnetically ordered spins due to the structural distortion. It is observed that the irradiated films show higher resistance than unirradiated films for all the compositions.

Electrical and magnetic properties of the pulsed laser deposited Ca doped LaMnO3 thin films on Si (100) and their electronic structures

We report the effect of Ca doping on the structural, electrical, magnetic and electronic properties of stoichiometric La1−xCaxMnO3 (x = 0, 0.3, 0.5 and 0.7) (LCMO) thin films grown on Si (100) using a pulsed laser deposition technique. All these films exhibit a single-phase orthorhombic structure with the space group Pnma. Physical properties, such as surface roughness, grain size, Curie temperature ‘Tc’, activation energy ‘Ea’ and magneto-resistance, were studied as a function of Ca doping. These properties were correlated with the variation of the observed electrical transport and magnetic properties and their electronic structures. The electronic structures of these films were studied by X-ray absorption spectroscopy (XAS) at O K and at Mn L3,2-edges, which indicate an admixture of Mn2+, Mn3+, and Mn4+ ions and also an increase in the density of states with Ca doping. These mixed valence states of Mn ions in LCMO arise due to the doping of Ca in the La sites, which modifies the electrical and magnetic properties.

Effect of gamma ray irradiation on the structural and electrical transport properties of PrFe1−xMnxO3

The effect of gamma ray irradiation on the structural and transport properties of polycrystalline bulk samples of PrFe1−xMnxO3 (x = 0.0, 0.1, 0.5) were investigated. The samples were synthesized by solid state reaction method and exposed to 60Co gamma radiation to accumulated dose of 625 KGy. From the Raman study, the modes exhibit a blue shift with broadening of spectral features in the irradiated samples. The dielectric constant (e′) was also studied as a function of frequency. The dielectric constant and ac conductivity increases with Mn doping but decrease on irradiation. Exposure to gamma radiation results in substantial modification in the physical properties of these compounds.