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Structural Study Of Mn-Doped Zno Fi Lms By Tem, Xingzhong Li, Jun Zhang, David J. Sellmyer
Structural Study Of Mn-Doped Zno Fi Lms By Tem, Xingzhong Li, Jun Zhang, David J. Sellmyer
David Sellmyer Publications
The structural study of diluted magnetic semiconductors is important for interpreting the ferromagnetic behavior associated with the materials. In the present work, a series of low concentration Mn-doped ZnO thin films synthesized by pulsed laser deposition was studied by electron microscopy. All films show the wurtzite structure with (001) preferred growth orientation on the Si substrate. Electron diffraction experiments indicate the deterioration of the growth orientation in some areas of the films with increasing Mn concentration, and the existence of a secondary phase, of Mn2O3-type, in the films with larger Mn concentrations. High-resolution electron microscopy images …
High-Energy Product Exchange-Spring Fept/Fe Cluster Nanocomposite Permanent Magnets, X. Rui, Jeffrey E. Shield, Zhiguang Sun, Lanping Yue, Yinfan Xu, David J. Sellmyer, Z. Liu, D.J. Miller
High-Energy Product Exchange-Spring Fept/Fe Cluster Nanocomposite Permanent Magnets, X. Rui, Jeffrey E. Shield, Zhiguang Sun, Lanping Yue, Yinfan Xu, David J. Sellmyer, Z. Liu, D.J. Miller
David Sellmyer Publications
In this paper, we report on the production of Fe cluster/FePt matrix nanocomposite permanent magnets. Monodispersed Fe clusters with sizes below 10 nm were formed by gas aggregation techniques. These Fe clusters were imbedded in an FePt matrix by alternate deposition from two sources. Specimens with a range of Fe cluster phase content from 0 to 30 vol% were produced by controlling deposition times from each source. As-deposited FePt formed in the A1 structure; thus, post-deposition heat treatment was necessary to form the hard magnetic L10 FePt compound. A single-step heat treatment at 600 °C for 10 min leads …
In-Cluster-Structured Exchange-Coupled Magnets With High Energy Densities, X. Rui, Jeffrey E. Shield, Zhiguang Sun, Yinfan Xu, David J. Sellmyer
In-Cluster-Structured Exchange-Coupled Magnets With High Energy Densities, X. Rui, Jeffrey E. Shield, Zhiguang Sun, Yinfan Xu, David J. Sellmyer
David Sellmyer Publications
In this letter, the authors demonstrate isotropic Fe–Pt exchange-spring nanocomposite permanent magnets with a soft magnetic phase fraction of greater than 0.5 with a coercivity of 6.5 kOe, single-phase-like magnetic behavior, and an energy product of 25.1 MG Oe. Sub-10-nm Fe–Pt clusters are formed with compositions in the two-phase Fe3Pt and FePt regions. Intracluster structuring on a scale of a few nanometers occurs after appropriate heat treatment. This ensures full exchange coupling between the two phases, allowing greater soft magnetic phase fractions. The results provide insight into developing high energy product nanostructured permanent magnets.
Ferromagnetic Properties Of Epitaxial Manganite Films On Srtio3/Si Heterostructures, Aswini K. Pradhan, J.B. Dadson, D. Hunter, K. Zhang, S. Mohanty, E.M. Jackson, B. Lasley-Hunter, K. Lord, T.M. Williams, Rakhim R. Rakhimov, Jun Zhang, David J. Sellmyer, K. Inaba, T. Hasewaga, S. Mathews, B. Joseph, B.R. Sekhar, U.N. Roy, Y. Cui, A. Burger
Ferromagnetic Properties Of Epitaxial Manganite Films On Srtio3/Si Heterostructures, Aswini K. Pradhan, J.B. Dadson, D. Hunter, K. Zhang, S. Mohanty, E.M. Jackson, B. Lasley-Hunter, K. Lord, T.M. Williams, Rakhim R. Rakhimov, Jun Zhang, David J. Sellmyer, K. Inaba, T. Hasewaga, S. Mathews, B. Joseph, B.R. Sekhar, U.N. Roy, Y. Cui, A. Burger
David Sellmyer Publications
We report on the magnetic properties of epitaxial La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on Si (100) and Si (111) substrates using SrTiO3 template layer, which demonstrate magnetic and electrical properties at and above room temperature. The magnetization data show magnetic transition and magnetic hysteresis at and above room temperature. The films show well-defined magnetic domains. The ferromagnetic resonance studies show anisotropic effects related to ferromagnetic properties of films. The smaller grain size of about 20 nm in manganite films on SrTiO3 /Si may be one of the reasons to …
Assembly Of High-Anisotropy L10 Fept Nanocomposite Films, David J. Sellmyer, Yinfan Xu, M. L. Yan, Yucheng Sui, Jian Zhou, Ralph Skomski
Assembly Of High-Anisotropy L10 Fept Nanocomposite Films, David J. Sellmyer, Yinfan Xu, M. L. Yan, Yucheng Sui, Jian Zhou, Ralph Skomski
David Sellmyer Publications
In this paper we report results on the synthesis and magnetic properties of L10 FePt nanocomposite films. Three fabrication methods have been developed to produce high-anisotropy FePt films: non-epitaxial growth of (0 0 1)-oriented FePt:X (X=Ag, C) composite films that might be used for perpendicular media; monodispersed FePt(CFx) core–shell nanocluster-assembled films grown with a gas-aggregation technique and having uniform cluster size and narrow size distribution; and template-mediated self-assembled FePt clusters prepared with chemical synthesis by a hydrogen reduction technique, which has a high potential for controlling both cluster size and orientation. The magnetic properties are controllable through …
Structural Effects On Exchange In Nanocluster Perpendicular Recording Media, J. Zhou, Ralph Skomski, David J. Sellmyer
Structural Effects On Exchange In Nanocluster Perpendicular Recording Media, J. Zhou, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
Nanostructured FePt: M (M=C,Ag,Cu) perpendicular magnetic recording media are investigated by numerical simulations and model calculations. Both intra- and intergranular exchanges are considered, and it is assumed that the interaction through the matrix is mediated by conduction electrons. Several limits, including free-electron-like Ruderman-Kittel-Kasuya-Yosida interactions, are considered. The atomic modeling yields effective intergranular coupling strengths that depend on both cluster radius and distance, on the magnetic properties of the clusters, and on the electronic nature of the medium. In the simulations, the exchange is approximated by a thin shell with reduced exchange and zero anisotropy. The simulations show that …
Fept Clusters Synthesized By Thermal Pyrolysis Of Fe And Pt Compounds In An Organic Solvent, Yucheng Sui, Yao Zhao, Maria Daniil, Xingzhong Li, David J. Sellmyer
Fept Clusters Synthesized By Thermal Pyrolysis Of Fe And Pt Compounds In An Organic Solvent, Yucheng Sui, Yao Zhao, Maria Daniil, Xingzhong Li, David J. Sellmyer
David Sellmyer Publications
A simple synthetic procedure involving the pyrolysis of Fe and Pt acetylacetonates mixed in trioctylamine results in the formation of alloy clusters with an average cluster around 4.2 nm and narrow size distribution. When the clusters are dispersed onto silicon wafers and heated under the protection of forming gas or nitrogen, the fcc structured clusters transform into hard magnetic FePt clusters with L10 chemical order. Coercivity values as high as 23 kOe are reached after rapid thermal annealing at 750 °C for 5 min.
Indirect Exchange In Dilute Magnetic Semiconductors, Ralph Skomski, J. Zhou, Jun Zhang, David J. Sellmyer
Indirect Exchange In Dilute Magnetic Semiconductors, Ralph Skomski, J. Zhou, Jun Zhang, David J. Sellmyer
David Sellmyer Publications
A generalized Ruderman-Kittel-Kasuya-Yosida (RKKY) approach is used to calculate indirect exchange interactions between localized spins in doped magnetic semiconductors. The exchange is mediated by electron or hole states centered around shallow impurities. The states hybridize and may or may not form a narrow band, but in both cases, the exchange is obtained from the hybridized states by second-order perturbation theory. As in the free-electron RKKY model, both positive and negative exchange interactions occur, but the strength Jij of the exchange is no longer a unique function of the distance between the localized spins. A closed expression with simple geometric interpretation …
Self-Assembled Nanocrystalline Epitaxial Manganite Films On Srtio3/Si Heterostructures, D. Hunter, J.B. Dadson, K. Zhang, B. Lasley, K. Lord, T.M. Williams, Rakhim R. Rakhimov, Aswini K. Pradhan, Jun Zhang, David J. Sellmyer
Self-Assembled Nanocrystalline Epitaxial Manganite Films On Srtio3/Si Heterostructures, D. Hunter, J.B. Dadson, K. Zhang, B. Lasley, K. Lord, T.M. Williams, Rakhim R. Rakhimov, Aswini K. Pradhan, Jun Zhang, David J. Sellmyer
David Sellmyer Publications
We report the growth and magnetic characterizations of La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on SrTiO3-buffered Si (100) and Si (111) substrates by pulsed-laser deposition. The structural studies show the epitaxial nature of the films. The microscopic studies show that the films consist of nanocrystalline particles. All films display sharp magnetic and electrical transitions associated with the colossal magnetoresistance behavior at and above room temperature, illustrating the superior quality of the films.
Finite-Temperature Anisotropy Of Magnetic Alloys, Ralph Skomski, O.N. Mryasov, J. Zhou, David J. Sellmyer
Finite-Temperature Anisotropy Of Magnetic Alloys, Ralph Skomski, O.N. Mryasov, J. Zhou, David J. Sellmyer
David Sellmyer Publications
The temperature dependence of the magnetic anisotropy of ferromagnetic materials is analyzed. Simple ferromagnets, such as Fe and Co, obey the m=n (n+1)/2 power laws predicted by the Callen and Callen [Phys. Rev. 129, 578 (1963)] theory, but in alloys, the applicability of the theory is an exception rather than the rule. Many alloys, such as the rare-earth transition-metal intermetallics and L10 magnets, violate a basic assumption of the theory, namely, that the single-ion anisotropy and the spontaneous magnetization have the same origin. This is the reason for significant deviations from the Callen and Callen …
Nanostructure And Magnetic Properties Of Highly (001) Oriented L10 (Fe49Pt51)1-XCuX Films, M.L. Yan, Yinfan Xu, David J. Sellmyer
Nanostructure And Magnetic Properties Of Highly (001) Oriented L10 (Fe49Pt51)1-XCuX Films, M.L. Yan, Yinfan Xu, David J. Sellmyer
David Sellmyer Publications
We report on nonepitaxially grown L10 Cu-alloyed FePt thin films with strong (001) texture. The FePt films with different Cu contents were deposited directly on Si wafers with a Fe49Pt51/Cu multilayer structure. The Cu content was varied from 0 to 13 at. %. All films were annealed at 600 °C for 5 min. X-ray-diffraction characterization showed that only one set of L10 diffraction peaks appeared and no elemental Cu diffraction peaks were visible. This result, along with a varying c/a lattice-parameter ratio, suggests that Cu substitutes Fe or Pt in the L1 …
Magnetic Reversal In Three-Dimensional Exchange-Spring Permanent Magnets, Jeffrey E. Shield, J. Zhou, S. Aich, V.K. Ravindran, Ralph Skomski, David J. Sellmyer
Magnetic Reversal In Three-Dimensional Exchange-Spring Permanent Magnets, Jeffrey E. Shield, J. Zhou, S. Aich, V.K. Ravindran, Ralph Skomski, David J. Sellmyer
David Sellmyer Publications
In this paper, we investigate the magnetization reversal in single-phase RE2Fe14B and two-phase α-Fe/RE2Fe14B with varying nanoscale grain structures and intergranular exchange interactions produced via controlled segregation during crystallization. We show that the loss of coercivity arises because domain-wall processes dominate the magnetic reversal as the exchange interactions increase. Micromagnetic modeling corroborates a transition to strongly cooperative magnetic reversal as the exchange interactions increase. The magnetic reversal is controlled by the growth of interaction domains via discrete domain-wall motion, and the coercivity is intrinsically limited by the presence of interaction domains. To …
Ferromagnetic Resonance Studies In Znmno Dilute Ferromagnetic Semiconductors, B. Lasley-Hunter, D. Hunter, Maxim Noginov, J.B. Dadson, K. Zhang, Rakhim R. Rakhimov, Aswini K. Pradhan, Jun Zhang, David J. Sellmyer
Ferromagnetic Resonance Studies In Znmno Dilute Ferromagnetic Semiconductors, B. Lasley-Hunter, D. Hunter, Maxim Noginov, J.B. Dadson, K. Zhang, Rakhim R. Rakhimov, Aswini K. Pradhan, Jun Zhang, David J. Sellmyer
David Sellmyer Publications
We report on the ferromagnetic resonance studies on ZnMnO films grown by the pulsed-laser deposition technique. ZnMnO films were annealed in different atmospheres. The films grown and annealed in oxygen demonstrate ferromagnetic behavior at room temperature and below. However, annealing in either nitrogen or argon deteriorates the ferromagnetic response of the films. Further annealing the films in oxygen recovers the ferromagnetic response. Our results suggest that oxygen plays a major role for controlling the ferromagnetic properties in ZnMnO films.
Oxide-Based Dilute Ferromagnetic Semiconductors: Znmno And Co:Tio2, Aswini K. Pradhan, D. Hunter, B. Lasley-Hunter, J.B. Dadson, Kai Zhang, Rakhim R. Rakhimov, Jun Zhang, David J. Sellmyer
Oxide-Based Dilute Ferromagnetic Semiconductors: Znmno And Co:Tio2, Aswini K. Pradhan, D. Hunter, B. Lasley-Hunter, J.B. Dadson, Kai Zhang, Rakhim R. Rakhimov, Jun Zhang, David J. Sellmyer
David Sellmyer Publications
We report on ferromagnetic properties of ZnMnO and Co:TiO2 films grown by pulsed laser deposition with varying growth conditions. We have demonstrated that ZnMnO films show ferromagnetic properties at room temperature. However, oxygen plays a dominant role in the occurrence of ferromagnetism. Introducing carriers into ZnMnO films did not improve the ferromagnetic properties. Our experimental results indicate that the mechanism for ferromagnetism lies, probably, within the perspective of charge transfer between Mn ions through oxygen. On the other hand, our experimental results suggest that the ferromagnetism in Co:TiO2 films is controlled by the presence of small metal Co …
Cluster-Assembled Nanocomposites, Yinfan Xu, M.L. Yan, David J. Sellmyer
Cluster-Assembled Nanocomposites, Yinfan Xu, M.L. Yan, David J. Sellmyer
David Sellmyer Publications
This chapter focuses on a gas-aggregation technique to prepare magnetic nanoclusters with controllable cluster sizes and size distributions. The review includes current research on nanoclusters, such as uncoated and oxide-coated Fe, Co and Fe clusters and clusters made from alloys, but special emphasis is on highly anisotropic L10-ordered FePt clusters, which are of potential interest for magnetic recording with ultrahigh areal densities of more than 1 Tera bit/in2. In particular, we discuss magnetic and structural properties of FePt nanoclusters and thin films. Another approach discussed in the chapter is to create cluster nanocomposites by multilayering …