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Structural and magnetic study of dysprosium substituted cobalt ferrite nanoparticles
Kumar, H.,Srivastava, R.C.,Pal Singh, J.,Negi, P.,Agrawal, H.M.,Das, D.,Hwa Chae, K. North-Holland Pub. Co 2016 Journal of magnetism and magnetic materials Vol.401 No.-
The present work investigates the magnetic behavior of Dy<SUP>3+</SUP> substituted cobalt ferrite nanoparticles. X-ray diffraction studies reveal presence of cubic spinel phases in these nanoparticles. Raman spectra of these nanoparticles show change in intensity of Raman bands, which reflects cation redistribution in cubic spinel lattice. Saturation magnetization and coercivity decrease with increase of Dy<SUP>3+</SUP>concentration in these nanoparticles. Room temperature Mossbauer measurements show the cation redistribution in these nanoparticles and corroborates the results obtained from Raman Spectroscopic measurements. Decrease in magnetization of Dy<SUP>3+</SUP> substituted cobalt ferrite is attributed to the reduction in the magnetic interaction and cation redistribution.
Consequences of electronic excitations in CoFe<sub>1.90</sub>Dy<sub>0.10</sub>O<sub>4</sub>
Kumar, H.,Singh, J.P.,Srivastava, R.C.,Negi, P.,Agrawal, H.M.,Asokan, K.,Won, S.O.,Chae, K.H. Elsevier 2015 CURRENT APPLIED PHYSICS Vol.15 No.12
Present work reports the irradiation induced effects in Dy<SUP>3+</SUP> doped cobalt ferrite nanoparticles in the regime of dominant electronic excitation processes induced by 100 MeV O<SUP>7+</SUP> ion irradiation. Irradiation leads to the deterioration of crystalline phase as envisaged by X-ray diffraction. Crystallite size decreases with the increase of irradiation fluence. Disappearance of certain bands in Raman spectra at higher fluence of irradiation confirms the crystalline disorder induced by electronic excitations. Fourier transform infrared spectra show onset of cation migration from tetrahedral site to octahedral site and vice versa. X-ray absorption fine structure measurements depict the preservation of valence state of metal ions after irradiation. These measurements further infer bond breaking process in irradiated materials. Magnetic measurements carried out on these materials indicate slight increase of saturation magnetization at room temperature followed by the decrease of coercive field. Obtained results are discussed on the basis of appropriate mechanism.
Magnetic Behaviour of Granular GdMnO3 Film
Negi, P.,Agrawal, H. M.,Singh, J. P.,Kumar, H.,Srivastava, R. C.,Asokan, K.,Chae, K. H. Springer Science + Business Media 2017 Journal of superconductivity and novel magnetism Vol.30 No.6
<P>The present study deals with the investigation of magnetic properties along with morphological and microstructure analyses of a multiferroic GdMnO3 film fabricated on Si(100) substrate by the pulsed laser deposition technique. Rutherford backscattering spectroscopic analysis suggests that the film is fabricated in the form of diffused layers having different stoichiometric proportions. Raman spectroscopy signifies that few modes present in the film are associated with MnO6 octahedra and some extra peaks indicating the mixed phase formation in tuning with the Rutherford backscattering spectroscopy. Atomic force microscopy confirms the granular nature of the film. Field-cooled and zero-field-cooled thermal magnetization curves show irreversible behaviour extending well above room temperature, which is associated with spin disorder. The presence of Gd+3 state and Mn+3/Mn+4 mixed states in the uppermost layers of the film was confirmed by near-edge X-ray absorption fine structure. Subsequently, in association with these observations, the film is a weak ferromagnetic at 5 K and even at room temperature.</P>
Jitendra Pal Singh,R.C. Srivastava,H.M. Agrawal,Prem Chand,Ravi Kumar 한국물리학회 2011 Current Applied Physics Vol.11 No.3
The present investigation aims to study the swift heavy ion irradiation induced effects in zinc ferrite nanoparticles through X-ray diffractometry, transmission electron microscopy and electron paramagnetic resonance spectroscopy. A series of zinc ferrite nanoparticles having different crystallite sizes ranging from 12 to 62 nm have been synthesized by using the nitrates of cations and the citric acid as the host. These samples were irradiated by 100 MeV oxygen beam with two fluences 1 × 10^13 and 5 × 10^13 ions/cm^2. The XRD patterns show the deterioration of crystalline phase after irradiation. The average crystallite size decreases after irradiation. EPR analyses of the pristine and irradiated samples show that the changes depend on the average crystallite size of the pristine samples. Further, the pristine sample having a crystallite size of 62 nm passes through dominant changes after irradiation. It was observed that the number of magnetic centres decreases in the irradiated samples.
Consequences of electronic excitations in CoFe1.90Dy0.10O4
Hemaunt Kumar,Jitendra Pal Singh,R.C. Srivastava,P. Negi,H.M. Agrawal,Kandasami Asokan,원성옥,채근화 한국물리학회 2015 Current Applied Physics Vol.15 No.12
Present work reports the irradiation induced effects in Dy3þ doped cobalt ferrite nanoparticles in the regime of dominant electronic excitation processes induced by 100 MeV O7þ ion irradiation. Irradiation leads to the deterioration of crystalline phase as envisaged by X-ray diffraction. Crystallite size decreases with the increase of irradiation fluence. Disappearance of certain bands in Raman spectra at higher fluence of irradiation confirms the crystalline disorder induced by electronic excitations. Fourier transform infrared spectra show onset of cation migration from tetrahedral site to octahedral site and vice versa. X-ray absorption fine structure measurements depict the preservation of valence state of metal ions after irradiation. These measurements further infer bond breaking process in irradiated materials. Magnetic measurements carried out on these materials indicate slight increase of saturation magnetization at room temperature followed by the decrease of coercive field. Obtained results are discussed on the basis of appropriate mechanism.