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1 May 2007

Volume 101, Issue 9, Articles (09xxxx)

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back to top Oxide Magnetic Semiconductors

Influence of defects on the magnetism of Mn-doped ZnO

D. Iuşan, B. Sanyal, and O. Eriksson

J. Appl. Phys. 101, 09H101 (2007); http://dx.doi.org/10.1063/1.2709411 (3 pages) | Cited 18 times

Online Publication Date: 23 March 2007

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The properties of dilute magnetic semiconductors are usually strongly influenced by the defects present in the system. Ab initio calculations may provide valuable insight for the microscopic understanding of the interactions with defects. Here, we present studies of Mn-doped ZnO in the presence of several defects by a combined approach of ab initio electronic structure calculations using Korringa-Kohn-Rostoker-coherent potential approximation and Monte Carlo simulations (MCSs). Electronic structure and magnetic interactions have similar trends for wurtzite and zinc-blende crystal structures. A weak antiferromagnetic interaction has been found for 5% Mn doping in defect-free ZnO. Defects such as O vacancies and Zn interstitials lead to antiferromagnetic interactions between the Mn atoms, while Zn vacancies and oxygen substitution by nitrogen yield ferromagnetic interactions. As the concentration of Mn is low and the exchange interactions are short ranged, MCSs show small values of Curie temperatures (not more than 50 K). However, for a few cases with codoping of Mn and defects, we obtained higher Curie temperatures (around 130 K). Estimates of the Curie temperatures, assuming an average separation of the Mn atoms in the mean-field solution of Heisenberg model, are in very good agreement with the results obtained from MCS.
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75.50.Pp Magnetic semiconductors
71.20.Nr Semiconductor compounds
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.50.Dd Nonmetallic ferromagnetic materials
61.72.Yx Interaction between different crystal defects; gettering effect

Exchange interactions between magnetic ions and free carriers in ZnMnO: An electron paramagnetic resonance analysis

A. Ben Mahmoud, H. J. von Bardeleben, J. L. Cantin, E. Chikoidze, Y. Dumont, and A. Mauger

J. Appl. Phys. 101, 09H102 (2007); http://dx.doi.org/10.1063/1.2709755 (3 pages) | Cited 1 time

Online Publication Date: 29 March 2007

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The magnetic interactions in n-type conductive Zn0.66Mn0.34O thin films with carrier concentrations of 2×1018 cm−3 have been investigated by X-band electron paramagnetic resonance (EPR) technique. We observe exclusively a single exchange narrowed Mn related EPR spectrum characterized by antiferromagnetic exchange interactions. The presence of free carriers modifies the EPR spectra by shifting the resonance fields to lower values. The shift can be modeled by the carrier polarization induced local magnetic field.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.50.Pp Magnetic semiconductors
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
73.61.Ga II-VI semiconductors

Electron spin resonance and Raman studies of Mn-doped ZnO ceramics

The-Long Phan, Roger Vincent, David Cherns, Nguyen Xuan Nghia, Manh-Huong Phan, and Seong-Cho Yu

J. Appl. Phys. 101, 09H103 (2007); http://dx.doi.org/10.1063/1.2709756 (3 pages) | Cited 5 times

Online Publication Date: 29 March 2007

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In the present work, the influence of annealing on structure, electron spin resonance (ESR), and Raman scattering (RS) spectra of x at. % Mn-doped ZnO (x = 4 and 8) ceramic compounds has been systematically investigated. The samples were annealed at temperatures (Tan) between 400 and 1000 °C for 12 h. The obtained results revealed the strong dependence of x-ray diffraction, ESR, and RS spectra on the annealing temperature Tan. Mn2+ ions did not substitute into Zn2+ sites in samples annealed in the range of 400–600 °C but started to substitute into Zn2+ sites for annealing temperatures Tan>600 °C. The results of this investigation provide further insights into the physical processes occurring in Mn-doped ZnO materials due to annealing.
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76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
78.30.Fs III-V and II-VI semiconductors
75.50.Pp Magnetic semiconductors
61.72.Cc Kinetics of defect formation and annealing

First-principles investigations of Co- and Fe-doped SnO2

X. L. Wang, Z. Zeng, X. H. Zheng, and H. Q. Lin

J. Appl. Phys. 101, 09H104 (2007); http://dx.doi.org/10.1063/1.2709740 (3 pages) | Cited 11 times

Online Publication Date: 30 March 2007

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We have investigated the electronic and magnetic properties of Co- and Fe-doped SnO2 by first-principles methods. The obtained results show that the ferromagnetic order is energetically much favored relative to the antiferromagnetic order in all the considered models of Co- and Fe-doped SnO2. The exchange interaction between Co ions is a long-range ferromagnetic interaction and gradually weakened as the distance between Co ions increases. For Fe-doped SnO2, the exchange interaction is also a long-range ferromagnetic one, but it oscillates with the variation of the distances between Fe ions. In addition, we further probe the concentration effect on the magnetic properties in the doped systems. The obtained results show that the exchange interaction between Co and Fe ions is reduced, implying that the enhancement of Curie temperature is not favored by increasing Co- and Fe-doping concentrations.
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75.50.Pp Magnetic semiconductors
75.10.Jm Quantized spin models, including quantum spin frustration
75.30.Et Exchange and superexchange interactions
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.70.Gm Exchange interactions

Ferromagnetism in sputtered manganese-doped indium tin oxide films with high conductivity and transparency

Toshihiro Nakamura, Kohei Tanabe, Kazuki Tsureishi, and Kunihide Tachibana

J. Appl. Phys. 101, 09H105 (2007); http://dx.doi.org/10.1063/1.2710324 (3 pages) | Cited 4 times

Online Publication Date: 30 March 2007

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Mn-doped indium-tin oxide (ITO) films were deposited on glass substrates using radio-frequency magnetron sputtering. The magnetization as a function of magnetic field showed hysteretic behavior at room temperature. According to the temperature dependence of the magnetization, the Curie temperature is higher than 400 K. Anomalous Hall effect was observed at low temperatures. Ferromagnetic thin films of Mn-doped ITO exhibited low electrical resistivity of 3.9×10−4 Ω cm and high optical transmittance between 75% and 90% in the visible region.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Le Other inorganic semiconductors

Vacancy mediated ferromagnetic interaction in TiO2 doped with magnetic ions

G. Cohen, V. Fleurov, and K. Kikoin

J. Appl. Phys. 101, 09H106 (2007); http://dx.doi.org/10.1063/1.2710239 (3 pages) | Cited 5 times

Online Publication Date: 10 April 2007

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We extend the model of ferromagnetic superexchange in dilute magnetic semiconductors to the ferromagnetically ordered highly insulating compounds (dilute magnetic dielectrics). The intrinsic ferromagnetism without free carriers is observed in oxygen-deficient films of anatase TiO2 doped with the transition metal impurities in cation sublattice. We suppose that ferromagnetic order arises due to superexchange between the complexes [oxygen vacancies+magnetic impurities], which are stabilized by a charge transfer from the vacancies to impurities. The Hund rule controls the superexchange via the empty vacancy related levels in the energy gap, so that it becomes possible only for the parallel orientation of impurity magnetic moments. The percolation threshold for magnetic ordering is determined by the radius of vacancy levels, but the exchange mechanism does not require free carriers. The crucial role of the nonstoichiometry in the formation of the ferromagnetism makes the Curie temperature extremely sensitive to the methods of sample preparation.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Hx Magnetic impurity interactions
75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters

Evidence for room temperature ferromagnetism in CuxZn1−xO from magnetic studies in CuxZn1−xO/CuO composite

M. S. Seehra, P. Dutta, V. Singh, Y. Zhang, and I. Wender

J. Appl. Phys. 101, 09H107 (2007); http://dx.doi.org/10.1063/1.2710453 (3 pages) | Cited 12 times

Online Publication Date: 17 April 2007

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Magnetic studies in bulk 57% CuxZn1−xO/43% CuO composite prepared chemically with x = 0.10 (0.03) are reported. Temperature dependence of the magnetic susceptibility shows clear signature of the Néel temperature TN ≃ 230 K for pure CuO. Hysteresis loop studies in the zero-field-cooled sample show room-temperature ferromagnetism with coercivity Hc ≃ 50 Oe at 300 K with strong temperature dependence for T<300 K. A negative exchange bias He at 5 K is observed when the sample is cooled from RT in H = 20 kOe, and its temperature dependence yields He→0 at TN = 230 K of CuO. These results and the temperature dependence of remanence Mr provide strong evidence that the CuxZn1−xO phase with x ≃ 0.10 is a ferromagnet with Tc ≃ 400 K. An electron magnetic resonance signal due to Cu2+ substituting for Zn2+ in CuxZn1−xO is also observed.
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75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Et Exchange and superexchange interactions

Engineering the magnetic properties of Ge1−xMnx nanowires

Olga Kazakova, Jaideep S. Kulkarni, Donna C. Arnold, and Justin D. Holmes

J. Appl. Phys. 101, 09H108 (2007); http://dx.doi.org/10.1063/1.2694052 (3 pages) | Cited 6 times

Online Publication Date: 20 April 2007

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Possible origins of room-temperature ferromagnetism in GeMn nanowires (NWs) are investigated. Arrays of Ge1−xMnx NWs and Ge/Ge1−xMnx nanocables (NCs) (x = 1%–5%) have been synthesized within the pores of anodized alumina oxide (AAO) membranes. The influence of annealing on the magnetic properties of Ge1−xMnx NWs is studied. The room-temperature ferromagnetism is preserved after the postfabrication annealing in inert atmosphere (Tann = 750 °C) demonstrating overall compatibility of Ge1−xMnx NWs with conventional complementary metal-oxide semiconductor technology. The role of oxygen in high-TC ferromagnetic ordering is investigated in double-phased NCs with a Ge sheath. Despite a barrier to oxygen migration from the AAO membrane, samples still display room-temperature ferromagnetism, hence, ruling out any significant role of oxygen in the explanation of the high TC in the system. The magnetic properties of the one-dimensional Ge1−xMnx nanostructures can be understood by considering interface related phenomena.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
81.40.Gh Other heat and thermomechanical treatments

Absence of ferromagnetism in V-implanted ZnO single crystals

Shengqiang Zhou, K. Potzger, H. Reuther, K. Kuepper, W. Skorupa, M. Helm, and J. Fassbender

J. Appl. Phys. 101, 09H109 (2007); http://dx.doi.org/10.1063/1.2710802 (3 pages) | Cited 9 times

Online Publication Date: 27 April 2007

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The structural and magnetic properties of V doped ZnO are presented. V ions were introduced into hydrothermal ZnO single crystals by ion implantation with fluences of 1.2×1016–6×1016 cm−2. Postimplantation annealing was performed in high vacuum from 823 to 1023 K. The ZnO host material still partly remains in a crystalline state after irradiation and is partly recovered by annealing. The V ions show a thermal mobility as revealed by depth profile Auger electron spectroscopy. Synchrotron radiation x-ray diffraction revealed no secondary phase formation which indicates the substitution of V onto Zn site. However, in all samples no pronounced ferromagnetism was observed down to 5 K by a superconducting quantum interference device magnetometer.
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75.50.Pp Magnetic semiconductors
61.66.Fn Inorganic compounds
61.72.Cc Kinetics of defect formation and annealing
79.20.Fv Electron impact: Auger emission

Fe valence states and ferromagnetism occurring in reduced anatase Ti0.97Fe0.03O2−δ

Hi Min Lee and Chul Sung Kim

J. Appl. Phys. 101, 09H110 (2007); http://dx.doi.org/10.1063/1.2710459 (3 pages) | Cited 3 times

Online Publication Date: 1 May 2007

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Fe-doped anatase TiO2 polycrystalline films and powders have been prepared by the sol-gel method. Air-annealed film shows paramagnetic behavior at room temperature. However, when the film is further annealed in a vacuum, the ferromagnetic properties are strongly enhanced with the magnetic moment of 0.42 μB/Fe at 5 kOe. Mössbauer spectrum of air-annealed film at 295 K shows a single doublet of Fe3+. On the other hand, the absorption spectrum after vacuum annealing exhibits two doublets, in which one is the same component with air-annealed case and the other is a new doublet corresponding to Fe2+ state. The temperature dependence of absorption linewidth and quadrupole splitting for the Fe2+ doublet indicates that Fe2+ ions are not paramagnetic and their magnetic interaction exists also at 295 K.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
75.30.Cr Saturation moments and magnetic susceptibilities
76.80.+y Mössbauer effect; other γ-ray spectroscopy
71.70.Jp Nuclear states and interactions

Structural and magnetic properties of Mn-doped CuO thin films

Hao Zhu, Fan Zhao, Liqing Pan, Yaping Zhang, Chongfei Fan, Yue Zhang, and John Q. Xiao

J. Appl. Phys. 101, 09H111 (2007); http://dx.doi.org/10.1063/1.2711711 (3 pages) | Cited 11 times

Online Publication Date: 2 May 2007

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Highly (111) oriented Mn(6.6%–29.8%) doped CuO thin films have been fabricated on thermally oxidized silicon substrate by radio-frequency magnetron sputtering. X-ray photoelectronic spectroscopy and resistivity studies indicate that both Cu and Mn ions have 2+ valences in the film. Ferromagnetism has been observed for 15.2%–29.8% Mn doped CuO thin film with a transition temperature between 87.0 and 99.5 K. The origin of ferromagnetism is analyzed in the context of competition among several interactions between Mn and Cu ions. Highly resistive nature of the films eliminates the carrier mediate mechanisms. The ferromagnetism arises from the ferromagnetic coupling between Mn ions mediated by Cu ions.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
79.60.Dp Adsorbed layers and thin films
68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films

Mapping ferromagnetism in Ti1−xCoxO2: Role of preparation temperature (200–900 °C) and doping concentration (0.000 15 ⩽ x ⩽ 0.1)

K. M. Reddy and A. Punnoose

J. Appl. Phys. 101, 09H112 (2007); http://dx.doi.org/10.1063/1.2712020 (3 pages) | Cited 4 times

Online Publication Date: 3 May 2007

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Based on the conflicting reports in the literature, an extensive investigation to map room-temperature ferromagnetic regimes in the Ti1−xCoxO2 system has been undertaken by studying 70 different sol-gel synthesized nanopowder samples by systematically varying x and/or annealing temperatures TA in the 0.000 15 ⩽ x ⩽ 0.1 and 200–900 °C ranges, respectively. The evolved map demonstrates interesting roles of x and TA resulting in localized regions and pockets of ferromagnetic behavior ( ⩽ 0.32μB) which changes gradually to larger nonferromagnetic regions. In general, the ferromagnetic regimes occur at higher Co concentrations as TA increases. X-ray diffraction studies showed a gradual decrease in temperature range at which the anatase-to-rutile transformation occurs in Ti1−xCoxO2 as x increased from 0 to 0.1. Co doping also lowered the band gap energy.
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75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.72.S- Impurities in crystals
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials

Interpretation of ferromagnetic Fe doped ZnO by Mössbauer spectroscopy

Seung-Iel Park, Geun Young Ahn, and Chul Sung Kim

J. Appl. Phys. 101, 09H113 (2007); http://dx.doi.org/10.1063/1.2712527 (3 pages) | Cited 4 times

Online Publication Date: 3 May 2007

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Single phase Zn0.95Fe0.05O sample was obtained by the sol-gel method with annealing at 650 °C for 6 h in H2 5%/Ar balance gas atmosphere. The crystalline structure of Zn0.95Fe0.05O is determined to be a P63mc hexagonal structure with lattice constants a0 = 3.255 Å and c0 = 5.207 Å at room temperature. The Mössbauer spectra were obtained at various temperatures ranging from 4.2 to 295 K. The values of the isomer shifts (δ) show that for all temperature ranges, they are in the ferrous (Fe2+) state. The magnetic hyperfine field (Hhf) and electric quadrupole splitting (ΔEQ) in the weak ferromagnetic state at 4.2 K have been analyzed, yielding the following results: Hhf = 37.8 kOe, θ = 67.5°, φ = 0°, η = 0.75, ΔEQ = 2.06 mm/s, and R = 7.4, respectively. From the Mössbauer spectrum at 77 K, the paramagnetic quadrupole phase is related to the temperature dependence of spin-lattice relaxation.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
76.80.+y Mössbauer effect; other γ-ray spectroscopy
71.70.Jp Nuclear states and interactions
61.66.Fn Inorganic compounds

Ordering in diluted magnetic semiconductors: A magnetic percolation phenomenon (invited)

O. Eriksson, D. Iuşan, R. Knut, and B. Sanyal

J. Appl. Phys. 101, 09H114 (2007); http://dx.doi.org/10.1063/1.2713220 (6 pages) | Cited 5 times

Online Publication Date: 4 May 2007

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We report on first principles calculations that describe the electronic structure, magnetic exchange interactions, and ordering temperatures of diluted magnetic semiconductors. The calculated interatomic exchange couplings are used in a Heisenberg Hamiltonian, and ordering temperatures are calculated with the use of Monte Carlo simulations. The accuracy of the method is analyzed by comparing observed and calculated ordering temperatures of several Mn and Cr doped III-V and II-VI semiconductors. The effect of magnetic percolation is discussed along with clustering phenomena and the effect of strong electron-electron interaction.
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75.50.Pp Magnetic semiconductors
75.30.Et Exchange and superexchange interactions
71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
75.10.Jm Quantized spin models, including quantum spin frustration

Investigation of the local Fe magnetic moments at the grain boundaries of the Ca2FeReO6 double perovskite

C. Azimonte, E. Granado, J. C. Cezar, J. Gopalakrishnan, and K. Ramesha

J. Appl. Phys. 101, 09H115 (2007); http://dx.doi.org/10.1063/1.2714317 (3 pages) | Cited 4 times

Online Publication Date: 7 May 2007

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The local Fe ferromagnetic (FM) moment at the grain boundaries of a ceramic sample of Ca2FeReO6 double perovskite was investigated by means of x-ray magnetic circular dichroism spectroscopy at the Fe L2,3 edges and compared to the overall bulk magnetization. We found that, at the grain boundaries, the Fe FM moments at H = 5 T are much smaller than expected and that the M×H curve is harder than in the bulk magnetization. These results suggest a larger degree of Fe/Re antisite disorder at the grain boundaries of this sample, shedding light into the intriguing nonmetallic resistivity behavior despite the reported presence of free carriers.
Show PACS
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
61.72.J- Point defects and defect clusters

Room-temperature fabricated ZnCoO diluted magnetic semiconductors

Hsin-Hung Huang, Chih-An Yang, Po-Hsiang Huang, Chih-Huang Lai, T. S. Chin, H. E. Huang, H. Y. Bor, and R. T. Huang

J. Appl. Phys. 101, 09H116 (2007); http://dx.doi.org/10.1063/1.2713210 (3 pages) | Cited 13 times

Online Publication Date: 8 May 2007

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(0002) textured and epitaxial ZnCo0.07O films were fabricated at room temperature by ion beam deposition on Si substrates. Hall measurement revealed that ZnCo0.07O films were n-type semiconductors with carrier concentrations higher than 1019/cm3. The carrier concentration of ZnCo0.07O can be manipulated by controlling the oxygen flow rate during deposition or by postannealing. The saturation magnetization and magnetoresistance ratios strongly depended on the carrier concentration. In addition, epitaxial (0002) ZnCo0.07O films, grown on Cu underlayers, showed room-temperature ferromagnetism, which may be potentially used for spintronic devices.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Ga II-VI semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects

Room temperature ferromagnetism in Cr-doped In2O3 on high vacuum annealing of thin films and bulk samples

P. Kharel, C. Sudakar, M. B. Sahana, G. Lawes, R. Suryanarayanan, R. Naik, and V. M. Naik

J. Appl. Phys. 101, 09H117 (2007); http://dx.doi.org/10.1063/1.2712175 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2007

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We report on the observation of room temperature ferromagnetism in Cr-doped In2O3 bulk samples and spin-coated thin films. The samples showed a clear ferromagnetism above 300 K with magnetic moments of 0.008 and 0.22 μB/Cr at 300 K for the bulk and thin film, respectively, only after high vacuum (HV) annealing at 600 °C. The vacuum annealed Cr-doped In2O3 thin films showed a typical semiconducting behavior with a room temperature resistivity of 0.73 Ω cm, while bulk samples were more conducting (23 mΩ cm). We present systematic investigations on the influence of HV annealing on the carrier concentrations, resistivity, and magnetic properties of the samples.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.30.Cr Saturation moments and magnetic susceptibilities
73.61.Le Other inorganic semiconductors
61.72.Cc Kinetics of defect formation and annealing

Magnetism in Zn1−xCoxO (0 ⩽ x<0.1) and Co3−yZnyO4 (y = 0, 0.25, and 1) thin films

C. Sudakar, P. Kharel, G. Lawes, R. Suryanarayanan, R. Naik, and V. M. Naik

J. Appl. Phys. 101, 09H118 (2007); http://dx.doi.org/10.1063/1.2712305 (3 pages) | Cited 2 times

Online Publication Date: 9 May 2007

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We have investigated the properties of homogeneous spinel Co3−yZnyO4 (y = 0, 0.25, and 1) and wurtzite CoxZn1−xO (0<x<0.1) films. Air annealed Co3−yZnyO4 films were found to develop only a small magnetic moment ( ∼ 10−3μB/Co). Conversely, these samples exhibited greatly enhanced magnetic moments after vacuum annealing. The vacuum annealed films reveal the presence of Zn doped CoO, but no detectable Co metal clusters. When field cooled to 10 K, the hysteresis curves of the vacuum annealed samples are displaced along the magnetization axis, which we attribute to uncompensated surface spins.
Show PACS
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Influence of Mn substitution on microstructure and magnetic properties of Cu1−xMnxO nanoparticles

G. Narsinga Rao, Y. D. Yao, and J. W. Chen

J. Appl. Phys. 101, 09H119 (2007); http://dx.doi.org/10.1063/1.2714190 (3 pages) | Cited 7 times

Online Publication Date: 10 May 2007

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Mn-doped CuO nanoparticles were synthesized using a coprecipitation method. Powder x-ray analysis reveals that all the samples crystallize into a monoclinic-type structure. Significant changes occur in both the microstructure and particle size with calcination temperature TA. The average particle size d increases from 11 to 85 nm as the TA increases from 250 to 850 °C. For particles of size d ⩽ 22 nm, energy dispersive spectroscopy indicates the existence of a crystalline Cu1−xMnxO core surrounded by an amorphous CuO shell. M(T) curves reveal a spin-glass behavior for the 11 and 22 nm particles and a ferromagnetic behavior for particles of size d ≥ 35 nm. The observed ferromagnetic behavior is attributed to the coexistence of Mn2+ and Mn3+ ions.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Lk Spin glasses and other random magnets
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.40.Gh Other heat and thermomechanical treatments

A variable temperature Fe3+ electron paramagnetic resonance study of Sn1−xFexO2 (0.00 ⩽ x ⩽ 0.05)

S. K. Misra, S. I. Andronenko, K. M. Reddy, J. Hays, A. Thurber, and A. Punnoose

J. Appl. Phys. 101, 09H120 (2007); http://dx.doi.org/10.1063/1.2709752 (3 pages) | Cited 13 times

Online Publication Date: 10 May 2007

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X-band ( ∼ 9.5 GHz) electron paramagnetic resonance (EPR) studies of Fe3+ ions in Sn1−xFexO2 powders with 0.00 ⩽ x ⩽ 0.05 at various temperatures (5–300 K) are reported. These samples are interesting to investigate as Fe doping ( ⩽ 5%) produces ferromagnetism in SnO2 [ A. Punnooose et al., Phys. Rev. B 72, 054402 (2005) ], making it a promising ferromagnetic semiconductor at room temperature. The EPR spectrum at 5 K can be simulated reasonably well as the overlap of spectra due to seven magnetically inequivalent Fe3+ ions: four low-spin (S = 1/2) and three high-spin (S = 5/2) ions, characterized by different spin-Hamiltonian parameters, overlapped by three broad ferromagnetic resonance spectra. The three high-spin ions, situated substitutionally in the interior of nanodomains, are characterized by smaller zero-field splitting (ZFS) parameters D and E, so that all their energy levels are populated at 5 K. On the other hand, the four low-spin ions are situated interstitially at the surfaces of nanodomains. They are characterized by much larger ZFS, so that only their lowest Kramers doublets are occupied at 5 K. Based on this simulation, it is concluded that the observed spectra at different temperatures can be reproduced by changing appropriately the relative overlaps of the various paramagnetic and ferromagnetic characters, which remain present over the temperature range studied.
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75.50.Pp Magnetic semiconductors
76.30.Fc Iron group (3d) ions and impurities (Ti-Cu)
75.50.Dd Nonmetallic ferromagnetic materials
75.10.Dg Crystal-field theory and spin Hamiltonians
71.20.Ps Other inorganic compounds
75.20.Ck Nonmetals

Large positive magnetoresistance effect below Curie temperature in In1.90−xMn0.1SnxO3

X. L. Wang, G. Peleckis, S. X. Dou, R. S. Liu, and J. G. Zhu

J. Appl. Phys. 101, 09H121 (2007); http://dx.doi.org/10.1063/1.2714192 (3 pages) | Cited 1 time

Online Publication Date: 11 May 2007

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We report on the magnetoresistance (MR) and magnetic properties of In1.90−xMn0.1SnxO3 (0 ⩽ x ⩽ 0.06) oxide. All samples were found to be ferromagnetic below TC = 46 K. Sn doping changed In1.90Mn0.1O3 from an insulator to a highly conducting phase at 300 K. A positive MR effect was observed over a wide temperature range just below TC. Calculated MR values reached a maximum of 20% at 5 K. A change in the MR effect, from positive to negative, occurred under magnetic field H>4 T at 5 K. The results of x-ray absorption near-edge spectroscopy indicated that Mn ions are present both as Mn2+ and Mn4+.
Show PACS
75.47.De Giant magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects
78.70.Dm X-ray absorption spectra
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