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Ferromagnetic Properties of Bulk Fe-doped CeO2 Dilute Magnetic Semiconductors
S. K. Sharma,M. Knobel,C. T. Meneses,샤런드라쿠마르,Y. J. Kim,B. H. Koo,이찬규,D. K. Shukla,Ravi Kumar 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3
Polycrystalline Fe-doped Ce1−xFexO2−δ has been fabricated by using the standard solid state reaction technique in the concentration range 0 ≤ x ≤ 0.05. Reitveld refinement of the X-ray diffraction patterns shows a pure CeO2 phase when x ≤ 0.03, and the appearance of a secondary impurity phase of Fe2O3 beyond that. Furthermore, by doping Fe into CeO2 powder, the ferromagnetism can be significantly enhanced to a maximum value for x = 0.03, but degrades quickly with further doping. Magnetization results reveal that the large room-temperature ferromagnetism observed in Fe-doped CeO2 powder originates from a combined effect of oxygen vacancies and transition metal doping.
INFLUENCE OF Co DOPING ON STRUCTURAL, OPTICAL AND MAGNETIC STUDIES OF Co-DOPED CeO2 NANOPARTICLES
SHALENDRA KUMAR,B. H. KOO,S. K. SHARMA,M. KNOBEL,C. G. LEE 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2010 NANO Vol.5 No.6
We have used the co-precipitation technique to synthesize nanocrystalline Co-doped CeO2 dilute magnetic semiconductors with Co concentrations ranging from 0.0–0.07. X-ray diffraction patterns (XRD) demonstrate that all the samples display single phase cubic structure without any impurity phase. Average particle sizes calculated from XRD and transmission electron microscopy (TEM) studies showed a gradual decrease with increase in Co ions concentration. UV–visible optical spectroscopy measurements reflect an energy band gap, which decreases with the increasing concentration of dopant (x ≤ 0.03). Raman spectra show an intensity loss of classical CeO2 vibration modes, which is an indication of considerable structural modifications and disorder in CeO2 lattice. Magnetic measurements revealed that all the samples exhibit a weak ferromagnetism at room temperature.
Kumar, Shalendra,Sharma, S.K.,Alimuddin, S.K.,Knobel, M.,Choudhary, R.J.,Lee, Chan Gyu,Koo, B.H.,Kumar, Ravi Elsevier 2009 Current Applied Physics Vol.9 No.5
<P><B>Abstract</B></P><P>We present here a comparative study on structural and magnetic properties of bulk and thin films of Mg<SUB>0.95</SUB>Mn<SUB>0.05</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> ferrite deposited on two different substrates using X-ray diffraction (XRD) and dc magnetization measurements. XRD pattern indicates that the bulk sample and their thin films exhibit a polycrystalline single phase cubic spinel structure. It is found that the film deposited on indium tin oxide coated glass (ITO) substrate has smaller grain size than the film deposited on platinum coated silicon (Pt–Si) substrate. Study of magnetization hysteresis loop measurements infer that the bulk sample of Mg<SUB>0.95</SUB>Mn<SUB>0.05</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> and its thin film deposited on Pt–Si substrate shows a well-defined hysteresis loop at room temperature, which reflects its ferrimagnetic behavior. However, the film deposited on ITO does not show any hysteresis, which reflects its superparamagnetic behavior at room temperature.</P>
Structural and magnetic properties of bulk and thin films of Mg0.95Mn0.05Fe2O4
샤런드라쿠마르,S.K. Sharma,Alimuddin,이찬규,B.H. Koo,M. Knobel,R.J. Choudhary,Ravi Kumar 한국물리학회 2009 Current Applied Physics Vol.9 No.5
We present here a comparative study on structural and magnetic properties of bulk and thin films of Mg0.95Mn0.05Fe2O4 ferrite deposited on two different substrates using X-ray diffraction (XRD) and dc magnetization measurements. XRD pattern indicates that the bulk sample and their thin films exhibit a polycrystalline single phase cubic spinel structure. It is found that the film deposited on indium tin oxide coated glass (ITO) substrate has smaller grain size than the film deposited on platinum coated silicon (Pt–Si) substrate. Study of magnetization hysteresis loop measurements infer that the bulk sample of Mg0.95Mn0.05Fe2O4 and its thin film deposited on Pt–Si substrate shows a well-defined hysteresis loop at room temperature, which reflects its ferrimagnetic behavior. However, the film deposited on ITO does not show any hysteresis, which reflects its superparamagnetic behavior at room temperature.
Ferromagnetism in Chemically-synthesized Co-doped ZnO
샤런드라쿠마르,Y. J. Kim,B. H. Koo,최희규,이찬규,S. K. Sharma,M. Knobel,S. Gautam,K. H. Chae 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3
We report room temperature ferromagnetism (RTFM) in Co-doped ZnO (Zn1−xCoxO; x = 0.01 − 0.05) powder synthesized using a co-precipitation method. Our magnetometry data reveal a weak FM behavior at RT in the range 0.01 < x < 0.05. FM by magnetic FM moment steadily decreases with increasing dopant. The O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra indicate that O vacancies increases with increasing Co concentration and that the sample with x ≥ 0.03 has more broadening at 535 and 540 eV, which may be due to the oxygen vacancies. Co in the ZnO host reveals a +2 oxidation state via the K edge NEXAFS spectra.
Structural and magnetic properties of chemically synthesized Fe doped ZnO
Kumar, Shalendra,Kim, Y. J.,Koo, B. H.,Sharma, S. K.,Vargas, J. M.,Knobel, M.,Gautam, S.,Chae, K. H.,Kim, D. K.,Kim, Y. K.,Lee, C. G. American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.105 No.7
<P>We report on the synthesis of Fe-doped ZnO with nominal composition of Zn0.99Fe0.01O by using a coprecipitation method. X-ray diffraction and selective area electron diffraction studies reveal a single phase wurtzite crystal structure without any secondary phase. Field emission transmission electron microscopy measurements infer that Zn0.99Fe0.01O have nanorod-type microstructures. Magnetic hysteresis measurement performed at different temperatures show that Zn0.99Fe0.01O exhibits a weak ferromagnetic behavior at room temperature. A detailed investigation of the electronic and local structure using O K-, Fe L-3,L-2 near edge x-ray absorption fine structure suggests that Fe is substituting Zn in ZnO matrix and is in Fe3+ state. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3073933]</P>