Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V22: Focus Session: Dilute Magnetic Oxide Semiconductors |
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP Chair: Berend Jonker, Naval Research Laboratory Room: 324 |
Thursday, March 19, 2009 8:00AM - 8:12AM |
V22.00001: A few ways in which LDA et al can produce a wrong description of magnetism in oxides Alex Zunger, S. Lany, H. Raebiger Part of the anarchy that exist in the literature regarding conflicting predictions of ferromagnetism in oxides can be attributed to problems in LDA and its application:(1) LDA et al tend to place the oxide conduction band minima CBM) at much too deep energies; transition-metal impurity levels then incorrectly appear within the (delocalized) LDA continuum (instead of in the gap). This leads to overly optimistic result of long -range magnetism. This is not fixable via LDA+U.(2) Oxides are naturally off-stoichiometric, exhibiting significant concentration of indigenous free-carriers that greatly affect the occupancy of impurity levels. Yet, such non-stoichiometry is ignored in many calculations using instead a perfect host crystals. This alters the magnetic properties. (3) LDA- Predicted magnetism in defected oxides without TM impurities often rely on the defect orbitals (e.g, cation vacancy) being equally delocalized over all of its ligand atoms. While inherent to LDA, experiment, as well as more correlated approaches reveal that such orbitals are ``locked'' instead onto a single ligand. This symmetry-breaking causes them to become too localized for (percolative) magnetism. We show here how such problems might be fixed. [Preview Abstract] |
Thursday, March 19, 2009 8:12AM - 8:24AM |
V22.00002: First-principles study of the effect of vacancies on magnetic properties Yoshi Kawazoe, Qian Wang, Qiang Sun, Puru Jena Due to the high solubility of Co in ZnO, the magnetic properties of Co-doped ZnO thin films have been extensively studied experimentally. Unfortunately, these results have led to diverse conclusions. To better understand the origin of the controversial experimental findings, we have carried out detailed theoretical studies, focusing on the role of concentration and distribution of Zn and O vacancies on the magnetism of Zn1-xCoxO thin films. We find that when Co atoms are substitutionally doped in ZnO thin films without any defects, the magnetic coupling between Co atoms is intrinsically anti-ferromagnetic. The coupling, however, changes to ferromagnetic when sufficient oxygen vacancies are introduced. On the other hand, Zn vacancies stabilize the anti-ferromagnetic coupling, in sharp contrast with that found in Zn1-xMnxO thin films. Our theoretical studies explain the origin of the different magnetic behavior observed experimentally. [Preview Abstract] |
Thursday, March 19, 2009 8:24AM - 8:36AM |
V22.00003: On the possibility of ferromagnetism in MgX (X = O, S, Se) with/without conventional magnetic atoms Van An Dinh, Kazunori Sato, Hiroshi Katayama-Yoshida We present a first principle study on the half-metallicity and ferromagnetism in rock salt MgZ (Z = O, S and Se) with and without conventional magnetic elements. The electronic structure, effective exchange coupling constant and chemical pair interaction are calculated within SIC-LSDA. The Curie temperature is predicted by performing Monte Carlo simulation. A possibility of spinodal decomposition is investigated and simulated. For transition-metal-doped MgO, our results reflect the observation in the experiment [1]. Without oxygen vacancy, Co- and Ni-doped MgO is anti-ferromagnetic. Except Ti and Cr, another transition metals cause the anti-ferromagnetic behavior in MgO. The ferromagnetism can be stabilized by oxygen vacancies. Oxygen vacancies also change the chemical interaction trend of transition metal atoms, and cause an inhomogeneous distribution in MgO. It is also found that N atoms which substitute for anions can introduce the half- metallic ground state and ferromagnetism in MgZ. Monte Carlo simulation shows the above room temperature ferromagnetism in Mg$_{0.8}$N$_{0.2}$Z. Nitrogen atoms in MgO and MgS have a tendency to create clusters, whereas the distribution of N atoms in MgSe is homogeneous at dilute regime. [1]. J. Narayan {\it et al.}, Appl. Phys. Lett. {\bf 93} (2008) 082507. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 8:48AM |
V22.00004: Ferromagnetism in MgO by Nitrogen Doping Cheng-Han Yang, Mahesh Samant, Stuart Parkin The new group, dilute ferromagnetic oxide and nitride, provides a promising technology potential to combine the magnetic and electronic properties. Studies in creating ferromagnetism in thin films of doped oxide materials without the inclusion of transition metal (TM) or rare-earth (RE) metal have been speculated in recent years. However, there have been many reports of ferromagnetism in large numbers of different material systems with poor control and reproducibility of these data. Our interest is exploring the possibility of ferromagnetism in oxide and nitride films without the introduction of any TM or RE elements. In this study, we have successfully incorporated substantial amounts of nitrogen upto 13 at{\%} into MgO films using molecular beam expitaxy (MBE) technique. N-doped MgO films were carried out by evaporating the Mg in the presence of both atomic oxygen and nitrogen from two different RF sources. Upon the post-annealing, N atoms generate holes on oxygen and so create magnetic moment as high as 0.4 $\mu $B/per N. In undoped MgO films, no magnetic signature was seen either in the as-deposited film or the film after annealing, which is a strong indication that the moment arises from the N dopants. The pre-edge feature of oxygen K-edge measured in Near Edge X-ray Absorption Fine Structure (NEXAFS) shows apparent evidence for the substitution of nitrogen for oxygen after post-annealing. [Preview Abstract] |
Thursday, March 19, 2009 8:48AM - 9:00AM |
V22.00005: Electric field control of magnetic semiconductor (Zn,Co)O Hyeon-Jun Lee, Erik Helgren, Frances Hellman The magnetic transport of a conducting Al(2{\%}) doped (Zn,Co)O-field-effect transistor is investigated at low temperature (2-10 K). The Al doped (Zn,Co)O channeling layer ($\sim $ 26 nm-thick) was deposited by magnetron sputtering at 550oC and processed into a 40 $\mu $m thick Hall bar geometry by photolithography and wet etching. An 80nm-thick AlOx layer was deposited at room temperature as the insulating barrier and Cr/Au was used as electrodes. The Hall effect and sheet resistance were measured from 2 - 10 K as a function of temperature, magnetic field and gate electric field. For gate electric field E=0V/cm, the electron concentration is 2.58 x 1014/cm2 at 5 K and there is no anomalous Hall effect. This carrier concentration is experimentally shown (by the Hall effect) to be tuned by $\pm$ 7.0 x 1012/cm2 with E=$\pm$4MV/cm. Application of E=+4 MV/cm induces magnetism in the channel layer as seen by an anomalous Hall effect. These results show that the magnetic properties of (Zn,Co)O with Al-doping can be modulated by gate electric field at low temperature. This research was supported by both DOE and WIN. [Preview Abstract] |
Thursday, March 19, 2009 9:00AM - 9:12AM |
V22.00006: Electron mediated ferromagnetism in cobalt doped ZnO Su-Huai Wei, Aron Walsh, Juarez L.F. Da Silva The potential to simultaneously tune both charge and spin in spintronic materials has lead to great interest in searching room temperature dilute ferromagnetic semiconductors. Among them, cobalt doped ZnO has become a focus of attention due to its reported high T$_C$ and reversible cycling of FM ordering. Coupled with existing optical and electrical properties of ZnO, this makes it a potentially technologically essential material. However, the mechanism that leads to ferromagnetism in ZnO:Co is still under debate. Using band structure methods, we show that pure ZnO:Co has a weak preference for antiferromagnetic ordering. Stabilization of ferromagnetism is achieved only after the spin- down Co t$_{2d}$ states are occupied through n-type doping. Our results are compared with available experimental data and results obtained from different levels of theoretical calculations. The limitations of the methods adopted in previous calculations are discussed. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:24AM |
V22.00007: Origin of the co-dopant induced enhancement of ferromagnetism in (Zn,Mn)O Yan Zhu, Juexian Cao, Z.Q. Yang, Ruqian Wu Using the density functional calculations, we elucidate the mechanism of co-dopant induced enhancement of ferromagnetism of (Zn,Mn)O. Li and Cu atoms tends to segregate toward Mn atoms and strongly promote the ferromagnetic coupling via either RKKY or superexchange interaction. The hole states produced by either Li or Cu are rather delocalized and they are efficient in mediating magnetic ordering. These findings shed new light for the design of dilute magnetic semiconductors with co-dopants for spintronic applications. [Preview Abstract] |
Thursday, March 19, 2009 9:24AM - 9:36AM |
V22.00008: Synthesis and Magnetic Properties of Cobalt doped ZnO Nanowires Ramakrishna Podila, Jian He, Amar Nath, Apparao Rao Here we report the synthesis of cobalt (Co) doped ZnO nanowires using a chemical vapor deposition technique. About 50 mM aqueous solution of ZnCl$_{2}$ and Co (CH$_{3}$COO)$_{2}$ was injected (rate of 0.1ml/min)into a quartz tube reactor maintained at 550$^{^{\circ}}$C. A constant flow (10:1) of O$_{2}$ and H$_{2}$ was maintained at 500 sccm. The as-prepared nanowires are typically $\sim $1-2 micrometers in length and tens of nanometers in diameter. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were employed to confirm the presence of the Co atoms in the nanowires. Significant ferromagnetism was observed in the 2 atomic {\%} Co-doped ZnO nanowires with a coercive field of 50 Oe. Furthermore, no saturation of magnetic moment was observed up to a field of 5T and 5K. A Curie-Weiss law fit to the temperature dependent magnetic susceptibility data yielded a magnetic moment $\mu $=1.99$\mu _{B}$ for Co$^{2+}$ ion, consistent with the low spin state. Based on Hall measurements and Seebeck coefficient data, the nature of the carriers and origin of magnetism in Co doped ZnO nanowires will be presented. [Preview Abstract] |
Thursday, March 19, 2009 9:36AM - 9:48AM |
V22.00009: Search for ferromagnetism in transition metal doped ZnO nano-clusters Indra Dasgupta, Nirmal Ganguli, Biplab Sanyal We present a comprehensive study of the energetics and magnetic interactions in 3d transition metal doped ZnO clusters by ab-initio density functional calculations. We find an important evidence that the charge state of the dopant transition element located at the surface of the cluster is different from that expected in the bulk and has a crucial impact on their magnetic properties. In addition, our calculations clearly reveal defects namely Zn and O vacancies in ZnO in neutral and charged states can induce ferromagnetic interactions between the transition metal atoms whereas anti ferromagnetic coupling dominates in a neutral defect-free cluster. Our results can have significant contributions in the nano-engineering of defects to achieve desired ferromagnetic properties in spintronics applications. [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:00AM |
V22.00010: Magnetism of TiO and TiO$_{2}$ Clusters Xiaohui Wei, Ralph Skomski, B. Balamurugan, Z. Sun, D.J. Sellmyer Ferromagnetism in wide-bandgap semiconductors has sparked interest due to its potential applications in spintronic devices$^{1}$. Previous research has focused on doped TiO$_{2}$ thin films, with little work on undoped TiO$_{2}$ and no report on TiO clusters. To investigate the magnetism of small TiO$_{x}$ particles, TiO$_{2}$ and TiO clusters with sizes from 15 to 50 nm were produced by inert gas condensation and examined with TEM, AFM, XRD, and SQUID. Ferromagnetism was found within the investigated temperature range of 10 to 400 K for all clusters including TiO. Interestingly, all clusters exhibit a magnetization enhancement after exposure in air for an extended time, which is probably due to the generation of oxygen vacancies and of Ti$^{3+}$ or Ti$^{2+}$, whose coupled spins may create the observed ferromagnetism$^{2}$. The relationship between cluster structure, size, defects and magnetism will be discussed. - This research is supported by NSF-MRSEC, ONR and NCMN. $^{1}$J. M. D. Coey, Curr. Opin. Solid State Mater. Sci. \textbf{10,} 83 (2006) $^{2}$S. Yoon, J. Phys.: Condens. Matter \textbf{18}, L355 (2006) [Preview Abstract] |
Thursday, March 19, 2009 10:00AM - 10:12AM |
V22.00011: Structural and magnetic characterization of (TM=Co, Fe) doped SnO$_{2 }$ nanostructures A. Parra Palomino, M.S. Rzchowski, O. Perales Perez Recent indications of intrinsic room-temperature (RT) ferromagnetism in transition metal doped-SnO$_{2}$ have increased its attractiveness as promising material for nano-optoelectronic and spintronics-based devices. A control over dopant speciation and the determination of the size-dependence of the properties at the nanoscale, become then indispensable. We present here the conditions for the room-temperature synthesis of doped SnO$_{2}$ in ethanol using SnCl$_{2}$ and LiHO precursors, and the characterization of the resulting bare, Co and Fe- doped SnO$_{2}$ powders. X-ray diffraction patterns of bare and doped SnO$_{2}$ showed the formation of an amorphous structure from the produced powder at RT. However, a pure phase of rutile structure was observed when the samples were annealed in air or Ar at 400$^{\circ}$C. 100nm diameter wires were observed after annealing using scanning electron microscopy (SEM). The results of magnetic characterization of the materials using a vibrating sample magnetometer (VSM) will also be presented and discussed. [Preview Abstract] |
Thursday, March 19, 2009 10:12AM - 10:24AM |
V22.00012: Structure and Magnetotransport Properties of High-T$_{C}$ Ferromagnetic Semiconductors, (Ba,Sr)\textit{M}$_{2\pm x}$Ru$_{4\pm x}$O$_{11}$ with \textit{M} = Mn, Fe, Co Larysa Shlyk, Rainer Niewa, Barbara Schuepp-Niewa, Lance De Long We have grown single crystals of R-type ferrites, (Ba,Sr)M$_{2\pm x}$Ru$_{4\pm x}$O$_{11}$ (M = Mn, Fe, Co), with compositions determined from X-ray refinements and microprobe analysis. The hexagonal crystal structure (P6$_{3}$/mmc, Z = 2) consists of (001) layers of edge-sharing (M,Ru)O$_{6}$ octahedra connected within [001] by face-sharing pairs of (M,Ru)$_{2}$O$_{9}$ octahedra and MO$_{5 }$trigonal bipyramids. A significant homogeneity range is generated by variable occupation of octahedral sites by 3d and 4d elements. These compounds are soft ferromagnetic semiconductors with T$_{C}$'s that can substantially exceed room-temperature, depending on composition. The temperature-dependent, in-plane (current parallel to \textbf{ab-}plane) resistivity of SrFe$_{2.51}$Ru$_{3.42}$Al$_{0.07}$O$_{11}$ indicates semiconductivity, and exhibits activated behavior with narrow gap of $\Delta \quad \approx $ 30 meV for T $>$180 K. Hall measurements show the predominant charge carriers are holes; our results suggest these materials are promising for spintronic devices. [Preview Abstract] |
Thursday, March 19, 2009 10:24AM - 10:36AM |
V22.00013: Hall effect in magnetic semiconductor InMnSb epitaxial thin films Nikhil Rangaraju, Nidhi Parashar, Bruce Wessels The magnetotransport properties of ferromagnetic $In_{1-x}Mn_{x}Sb$ semiconductor films with x=0.01 to 0.035 were measured from 1.5 K to 298K and magnetic fields up to 18T. The vapor phase epitaxial films are p-type with a hole concentration of $10^{19}~cm^{-3}$ and mobility of $10^{2}~cm^{2}/Vs$. The Hall resistivity is described by the equation $\rho_{xy}=R_{0}B+R_{A}M$ where $R_{0}$ and $R_{A}$ are the normal and anomalous hall coefficients, $B$ is the applied magnetic field and M is the magnetization. The films exhibited an anomalous Hall effect over entire temperature range. It was observed that $R_{A}$ is proportional to the longitudinal resistivity $(\rho_{xx})$ leading to a magnetoresistance dependant Hall voltage. [Preview Abstract] |
Thursday, March 19, 2009 10:36AM - 10:48AM |
V22.00014: Magnetotranport properties of magnetic InMnSb semiconductor films. Nidhi Parashar, Nikhil Rangaraju, Bruce Wessels Magnetotransport properties of the magnetic semiconductor In$_{1-x}$M$_{x}$nSb were investigated for temperatures from 1.4 to 300 K and magnetic fields up to 18 T. Films are $p$-type, with carrier concentration $\sim $ 10$^{19}$ cm$^{-3}$, and exhibit anomalous Hall Effect at room temperature. At low temperatures and low fields, negative magnetoresistance of 4 percent was observed, for a film with x = 0.035. For higher fields, a positive magnetoresistance of 9 percent was observed. At 300 K, positive magnetoresistance with hysteretic behavior was observed. The magneto-resistive properties are analyzed with respect to recent models of spin-dependent scattering in magnetic semiconductors. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700