K. Asokan

Magnetic and electrical properties of In doped cobalt ferrite nanoparticles

Nanoparticles of CoFe2O4 and CoIn0.15Fe1.85O4 ferrites were prepared by citrate gel route and characterized to understand their structural, electrical, and magnetic properties. X-ray diffraction and Raman spectroscopy were used to confirm the formation of single phase cubic spinel structure. The average grain sizes from the Scherrer formula were below 50u2009nm. Microstructural features were obtained by scanning electron microscope and compositional analysis by energy dispersive spectroscopy. The hysteresis curve shows enhancement in coercivity while reduction in saturation magnetization with the substitution of In3+ ions. Enhancement of coercivity is attributed to the transition from multidomain to single domain nature. Electrical properties, such as dc resistivity as a function of temperature and ac conductivity as a function of frequency and temperature were studied for both the samples. The activation energy derived from the Arrhenius equation was found to increase in the doped sample. The dielectric cons...

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.

Study of structural property of Co ferrite thin film grown by pulsed laser deposition technique

Thin film of Cobalt Ferrite was deposited on Si (1 0 0) substrate using Pulsed Laser Deposition (PLD) technique. The deposited film was characterized by X–ray Diffraction (XRD), X–ray reflectivity (XRR), Rutherford Backscattering Spectroscopy (RBS) and Raman Spectroscopy and was found to be single phase, textured along (1 1 1) directions and approximately matching the stoichoimetry of the target with negligible strain. The film had a very uniform and flat surface. Raman spectroscopy measurement further confirmed the formation of single phase cubic spinel structure. T2g Raman mode was missing from the spectra which may be due to cation redistribution and crystallite size effect.

Modification of Structural and Magnetic Properties of Masked Co–Pt Films Induced by High-Energy Ion Implantation

Magnetic and structural properties of Co80Pt20 films were modified by controlled ion implantation through a dot-patterned mask for possible application in the mass production of patterned recording media. The dot patterns were fabricated using self-assembly of di-block copolymers. The effects of 14N + and 40Ar+ ion implantation at energies as high as 40 and 100xa0keV, respectively, were studied. Although both ions cause changes in the structural and magnetic properties, 40 Ar+ ion implantation leads to more significant changes. The structural changes, predicted using simulations and experimentally observed using X-ray diffraction, indicate a mixing of Co into the layers below, leading to layers richer in Pt at the top. Magnetic force microscopy measurements show an increase in domain width and domain wall thickness as a function of ion fluences. The results are analyzed with measurements of magnetic anisotropy constant and micromagnetic simulations.

Tailoring the structural and magnetic properties of masked CoPt thin films using ion implantation

The effects of ion implantations through a mask on the structural and magnetic properties of Co80Pt20 films were investigated. The mask was patterned using the self-assembly of diblock copolymers. For implantation, high (40 keV for 14N+ and 100 keV for 40Ar+) and low (7.5 keV for 14N+ and 4.5 keV for 40Ar+) energy 14N+ and 40Ar+ ions were used to modify the structural and magnetic properties of these films. X-ray diffraction and TRIM simulations were performed for understanding the structural changes due to ion implantations. These results revealed the intermixing of Co atoms in lower layers and lattice expansion in Co80Pt20 magnetic and Ru layers. A lateral straggling of Co caused an increase in the exchange coupling in the masked region. Depletion of Co atoms in Co80Pt20 layer caused a decrease in the anisotropy constant, which were further confirmed by the alternating gradient force magnetometer and magnetic force microscopy results. The magnetic force microscopy images showed an increase in domain wid...

Broadband strip-line ferromagnetic resonance spectroscopy of soft magnetic CoFeTaZr patterned thin films

In this paper, magnetic and magnetization dynamic properties of compositionally patterned Co46Fe40Ta9Zr5 thin films are investigated. A combination of self-assembly and ion-implantation was employed to locally alter the composition of Co46Fe40Ta9Zr5 thin film in a periodic manner. 20 keV O+ and 60 keV N+ ions were implanted at different doses in order to modify the magnetization dynamic properties of the samples in a controlled fashion. Magnetic hysteresis loop measurements revealed significant changes in the coercivity for higher influences of 5 × 1016 ions per cm2. In particular, N+ implantation was observed to induce two phase formation with high and low coercivities. Broadband strip-line ferromagnetic resonance spectroscopy over wide range of frequency (8 – 20 GHz) was used to study the magnetization dynamics as a function of ion-beam dosage. With higher fluences, damping constant showed a continuous increase from 0.0103 to 0.0430. Such control of magnetic properties at nano-scale using this method is believed to be useful for spintronics and microwave device applications.In this paper, magnetic and magnetization dynamic properties of compositionally patterned Co46Fe40Ta9Zr5 thin films are investigated. A combination of self-assembly and ion-implantation was employed to locally alter the composition of Co46Fe40Ta9Zr5 thin film in a periodic manner. 20 keV O+ and 60 keV N+ ions were implanted at different doses in order to modify the magnetization dynamic properties of the samples in a controlled fashion. Magnetic hysteresis loop measurements revealed significant changes in the coercivity for higher influences of 5 × 1016 ions per cm2. In particular, N+ implantation was observed to induce two phase formation with high and low coercivities. Broadband strip-line ferromagnetic resonance spectroscopy over wide range of frequency (8 – 20 GHz) was used to study the magnetization dynamics as a function of ion-beam dosage. With higher fluences, damping constant showed a continuous increase from 0.0103 to 0.0430. Such control of magnetic properties at nano-scale using this method is...

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.