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  • 1.
    Araujo, C. Moysés
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Jun, Xu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Jayakumar, Onattu D.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Wu, Yan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Århammar, Cecilia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Gehring, Gillian A.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Room temperature ferromagnetism in pristine MgO thin films2010In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 96, no 23Article in journal (Refereed)
    Abstract [en]

    Robust ferromagnetic ordering at, and well above room temperature is observed in pure transparent MgO thin films (<170 nm thick) deposited by three different techniques. Careful study of the wide scan x-ray photoelectron spectroscopy rule out the possible presence of any magnetic contaminants. In the magnetron sputtered films, we observe magnetic phase transitions as a function of film thickness. The maximum saturation magnetization of 5.7 emu/cm(3) is measured on a 170 nm thick film. The films above 500 nm are found to be diamagnetic. Ab initio calculations suggest that the ferromagnetism is mediated by cation vacancies.

  • 2. Bhatt, P.
    et al.
    Kanciurzewska, A.
    Carlegrim, E.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov M.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Fahlman, M.
    Ferromagnetism above room temperature in nickel-tetracyanoethylene thin films2009In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 19, no 36, p. 6610-6615Article in journal (Refereed)
    Abstract [en]

    Room temperature ferromagnetic ordering is reported in Ni-tetracyanoethylene (TCNE) thin films fabricated on Au substrates using physical vapor deposition (PVD) under ultra high vacuum conditions. This technique enables the preparation of very clean films without having any kind of contamination from oxygen-containing species, solvents or precursor molecules. Film stoichiometry was obtained from X-ray photoelectron spectroscopy (XPS) measurements. XPS derived stoichiometry points to a similar to 1 : 2 ratio between Ni and TCNE resulting in Ni(TCNE)(x), x approximate to 2. No evidence of pure Ni metal in the in situ grown films was present in the XPS or the ultraviolet photoelectron spectroscopy (UPS) measurements within the detection limits of the techniques.

  • 3.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Defect Induced Room-Temperature Ferromagnetism in ZnO and MgO Thin FIlms and Device Development2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents the discovery of defect induced room-temperature ferromagnetism in industrially important ZnO and MgO thin films, and establishes from a systematic study, in both ZnO and MgO films, the unique phenomenon of the sequences of transitions from ferromagnetism to para-, and eventually the well known diamagnetism of the bulk as a function of film thickness.

    Highly oriented and high quality dense thin films of ZnO and MgO have been deposited by reactive (balanced) magnetron sputtering under different ambience conditions and deposition temperatures. The ZnO thin films were deposited from a Zn metal target whereas the MgO thin films were deposited from an MgO ceramic target. Their magnetic properties have been studied as a function of both film thickness and variation in oxygen deposition pressure (for a given thickness) using a SQUID magnetometer. The ferromagnetic ordering in these materials is shown to arise from lattice defects situated at the cation sites. We discuss in detail the observed variation in their saturation magnetization, MS, as a function of the various deposition conditions and film characteristics (i.e. film thickness), and relate these to the nature and role of the intrinsic defects in giving rise to the observed magnetism. The in-plane saturation magnetization obtained in these films is at least two orders of magnitude larger as compared to what is measured in nanoparticles of similar dimensions. Furthermore it is shown that the magnetic properties in these thin films is directional dependent and that along the diagonal of the wurtzite structure at 45 degrees to the c-axis the MS values are about 60% larger. This we correlate with a calculation based on the structure which shows that the cation- cation distances along the diagonal is the shortest by similar magnitude. A Zn57O57 super-cell has been modelled using the Inorganic Crystal Structure Database (ICSD Diamond 3.0), from which we have calculated the shortest distance between two adjacent cation sites (i.e. potential cation vacancy sites) along the c-axis as well as perpendicular and along the diagonal (i.e. 45°) to the c-axis (along which the films have grown). Such possibilities to tailor defect induced ferromagnetism resulting in saturation magnetization of ≈ 5 emu/g, is indeed highly important information in understanding and designing thin film devices. In order to further tailor the physical property of polycrystalline ZnO thin films, un-balanced magnetron sputtering was used to obtain porous microstructured ZnO thin films to induce significant UV photoconductivity and demonstrate plausible device application.

    The above studies have been made possible using extensive characterization of the high quality films, in the thickness range from a few nanometers to almost a micron, using XRD for structure, Dual beam HRSEM/FIB and AFM for accurate film cross-sectioning and surface morphology, EDXS for elemental analysis and electrical/photo- conductivity measurements over a wide range of incident radiation from UV to visible.

    The overall conclusion is that the room-temperature ferromagnetic ordering in the ZnO and MgO thin films originates from cation vacancies which couple ferromagnetically and establish long range magnetic order.

  • 4.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Effects of hole doping in the ferromagnetic semiconductor Mn-doped ZnO thin film studied by x-ray magnetic circular dichoism2009In: "Solid state devices and materials(SSDM2009)" held in Japan(7-9 october 2009), 2009Conference paper (Other academic)
  • 5.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Kloo, Lars
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Åkerstedt, Josefin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Inorganic Chemistry.
    Defect induced magnetic anisotropy in undopted ZnO thin filmsArticle in journal (Other academic)
  • 6.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Upadhyay, Ramesh Venkataramaia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Belova, Liubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of synthesis techniques on the magnetic properties of Mn-doped ZnO2008In: Magnetic Materials / [ed] Ghoshray, A; Bandyopadhyay, B, 2008, Vol. 1003, p. 255-257Conference paper (Refereed)
    Abstract [en]

    Mn-doped ZnO thin films have been prepared using three different routes, namely, magnetron sputtering technique, Pulsed Laser Deposition technique using targets from powders synthesized by solid state, and chemical method. Films deposited using sputtering technique in absence of nitrogen pressure gives higher magnetic moment per Mn atom, than is the case with films prepared by PLD indicating that ferromagnetism in the DMS systems is highly sensitive to processing conditions.

  • 7.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Xu, Jun
    Biswas, Anis
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Tamaki, Takahiko
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sharma, P.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belova, Lyuba
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Coexistence of ultraviolet photo-response and room-temperature ferromagnetism in polycrystalline ZnO thin films2010In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, ISSN 0167-577X, Vol. 64, no 11, p. 1291-1294Article in journal (Refereed)
    Abstract [en]

    The coexistence of ultraviolet (UV) photoconductivity (PC) and room-temperature ferromagnetism (RTFM) is observed in polycrystalline ZnO thin films deposited by unbalanced magnetron sputtering under high oxygen pressure. A significant increase in PC (similar to 870% to 40000%) is observed with increasing film thickness and the consequent structural disorder and film porosity. In contrast, the saturation magnetization (M(S)) at room temperature is found to decrease from 1.02 emu/g to 0.53 emu/g with increasing film thickness from 50 to 150 nm.

  • 8.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Xu, Jun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Carlegrim, Elin
    Fahlman, Mats
    Experimental evidence for ferromagnetism at room-temperature in MgO thin films2010In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 22, no 34, p. 345004-Article in journal (Refereed)
    Abstract [en]

    Ferromagnetic ordering at room temperature (RTFM) in MgO thin films deposited by RF magnetron sputtering under various atmospheric conditions and temperatures is reported. A saturation magnetization (MS) value as high as 1.58 emu g(-1) is (0.046 mu B/unit cell) observed for a 170 nm film deposited at RT under an oxygen pressure of 1.3 x 10(-4) mbar. In contrast, films deposited at elevated temperature (under an identical oxygen pressure), or at higher oxygen pressures, as well as under a nitrogen atmosphere at RT show significantly suppressed magnetization. The ferromagnetic order in the MgO matrix is believed to be defect induced

  • 9.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Xu, Jun
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    On the defect induced ferromagnetic ordering above room-temperature in undoped and Mn doped ZnO thin films2009In: NOVEL MATERIALS AND DEVICES FOR SPINTRONICS / [ed] Sanvito S, Heinonen O, Dediu VA, Rizzo N, Warrendale, PA: MATERIALS RESEARCH SOCIETY , 2009, Vol. 1183, p. 3-8Conference paper (Refereed)
    Abstract [en]

    Evidence for long range ferromagnetic order above room-temperature, RTFM, in pristine ZnO, In2O3, TiO2 nanoparticles and thin films, containing no nominal magnetic elements have been reported recently. This could question the origin of RTFM in doped dilute alloys if for example the ZnO matrix itself develops a defect induced magnetic order with a significant moment per unit cell. In this presentation we report a systematic study of the film thickness dependence of RTFM in pure ZnO deposited by DC Magnetron Sputtering. We observe a maximum in the saturation magnetization, Ms, value of 0.62 emu/g (0,018 ÎŒB/unit cell), for a -480 nm film deposited in an oxygen ambience of appropriate pressure. Above a thickness of around 1 ÎŒm the films are diamagnetic as expected. We thus see a sequential transition from ferromagnetism to para- and eventual diamagnetism as a function of film thickness in ZnO. We also find that in such a ZnO matrix with a maximum intrinsic defect induced moment, on doping with Mn the maximum enhanced Ms value of 0.78 emu/g is obtained for 1 at. % Mn doping. With this approach of appropriate doping in a defect tailored matrix, we routinely obtain RTFM in both undoped and Mn- doped ZnO thin films.

  • 10.
    Kapilashrami, Mukes
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Xu, Jun
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ström, Valter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Transition from ferromagnetism to diamagnetism in undoped ZnO thin films2009In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 95, no 3Article in journal (Refereed)
    Abstract [en]

    We report a systematic study of the film thickness dependence (0.1-1 mu m) of room-temperature ferromagnetism in pure magnetron-sputtered ZnO thin films wherein a sequential transition from ferromagnetism to paramagnetism and diamagnetism as a function of film thickness is observed. The highest saturation magnetization (M-S) value observed is 0.62 emu/g (0.018 mu(B)/unit cell) for a similar to 480 nm film. On doping the ZnO film with 1 at. % Mn enhances the M-S value by 26%. The ferromagnetic order in ZnO matrix is believed to be defect induced. In addition, on doping with Mn hybridization between the 2p states of O and the 3d states of Mn occurs.

  • 11. Kataoka, T.
    et al.
    Yamazaki, Y.
    Singh, V. R.
    Sakamoto, Y.
    Fujimori, A.
    Takeda, Y.
    Ohkochi, T.
    Fujimori, S. -I
    Okane, T.
    Saitoh, Y.
    Yamagami, H.
    Tanaka, A.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Belova, Liubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Rao, K. Venkat
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Engineering Material Physics.
    Ferromagnetism in ZnO co-doped with Mn and N studied by soft x-ray magnetic circular dichroism2011In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 13, p. 132508-Article in journal (Refereed)
    Abstract [en]

    We have investigated the electronic structure of ZnO:Mn and ZnO:Mn,N thin films using x-ray magnetic circular dichroism (XMCD) and resonance-photoemission spectroscopy. From the Mn 2p -> 3d XMCD results, it is shown that, while XMCD signals only due to paramagnetic Mn(2+) ions were observed in ZnO:Mn, nonmagnetic, paramagnetic, and ferromagnetic Mn(2+) ions coexist in ZnO:Mn,N. XMCD signals of ZnO:Mn,N revealed that the localized Mn(2+) ground state and Mn(2+) state hybridized with ligand hole coexisted, implying p-d exchange coupling. In the valence-band spectra, spectral weight near the Fermi level was suppressed, suggesting that interaction between magnetic moments in ZnO:Mn,N has localized nature. 

  • 12. Moeck, P.
    et al.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Portland State University (PSU), United States.
    Rao, Arvind
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Portland State University (PSU), United States.
    Aldushin, K.
    Lee, J.
    Morris, J. E.
    Browning, N. D.
    McCann, P. J.
    Nominal PbSe nano-islands on PbTe: Grown by MBE, analyzed by AFM and TEM2005Conference paper (Refereed)
    Abstract [en]

    Nominal PbSe nano-islands were grown in the Stranski-Krustanow mode on (111) oriented PbTe/BaF 2 pseudo-substrates by molecular beam epitaxy (MBE). The number density and morphology of these islands were assessed by means of atomic force microscopy (AFM). Transmission electron microscopy (TEM) was employed to determine the strain state and cryslallographic structure of these islands. On the basis of both AFM and TEM analyses, we distinguish between different groups of tensibly strained islands. The suggestion is made to use such nano-islands as part of nanometrology standards for scanning probe microscopy.

  • 13. Moysés Araújo, C.
    et al.
    Kapilashrami, Mukes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jun, Xu
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jayakumar, Onattu D.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nagar, Sandeep
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wu, Yan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Århammar, Cecilia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Belova, Lyubov
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ahuja, Rajeev
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Rao, K Venkat.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Unusual ferromagnetism above room temperature in undoped thin films and nanoparticles of MgOManuscript (Other academic)
1 - 13 of 13
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