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Full-Text Articles in Physics

Noncollinear Spin Structure In Fe3+Xco3−Xti2 (X = 0, 2, 3) From Neutron Diffraction, Haohan Wang, Balamurugan Balamurugan, Rabindra Pahari, Ralph Skomski, Yaohua Liu, Ashfia Huq, D. J. Sellmyer, Xiaoshan Xu Jan 2019

Noncollinear Spin Structure In Fe3+Xco3−Xti2 (X = 0, 2, 3) From Neutron Diffraction, Haohan Wang, Balamurugan Balamurugan, Rabindra Pahari, Ralph Skomski, Yaohua Liu, Ashfia Huq, D. J. Sellmyer, Xiaoshan Xu

Xiaoshan Xu Papers

Neutron powder diffraction has been used to investigate the spin structure of the hard-magnetic alloy Fe3+xCo3−xTi2 (x = 0, 2, 3). The materials are produced by rapid quenching from the melt, they possess a hexagonal crystal structure, and they are nanocrystalline with crystallite sizes D of the order of 40 nm. Projections of the magnetic moment onto both the crystalline c axis and the basal plane were observed. The corresponding misalignment angle exhibits a nonlinear decrease with x, which we explain as a micromagnetic effect caused by Fe-Co site disorder. The underlying physics is ...


Nonvolatile Voltage Controlled Molecular Spin State Switching, G. Hao, A. Mosey, X. Jiang, A. J. Yost, K. R. Sapkota, G. T. Wang, X. Zhang, J. Zhang, A. T. N'Diaye, R. Cheng, X. Xu, P. A. Dowben Jan 2019

Nonvolatile Voltage Controlled Molecular Spin State Switching, G. Hao, A. Mosey, X. Jiang, A. J. Yost, K. R. Sapkota, G. T. Wang, X. Zhang, J. Zhang, A. T. N'Diaye, R. Cheng, X. Xu, P. A. Dowben

Xiaoshan Xu Papers

Voltage-controlled room temperature isothermal reversible spin crossover switching of [Fe{H2B(pz)2}2(bipy)] thin films is demonstrated. This isothermal switching is evident in thin film bilayer structures where the molecular spin crossover film is adjacent to a molecular ferroelectric. The adjacent molecular ferroelectric, either polyvinylidene fluoride hexafluoropropylene or croconic acid (C5H2O5), appears to lock the spin crossover [Fe{H2B(pz)2}2(bipy)] molecular complex largely in the low or high spin state depending on the direction of ferroelectric polarization. In both a planar two terminal diode structure and ...


Nanostructural Origin Of Semiconductivity And Large Magnetoresistance In Epitaxial Nico2O4/Al2O3 Thin Films, Congmian Zhen, Xiaozhe Zhang, Wengang Wei, Wenzhe Guo, Ankit Pant, Xiaoshan Xu, Jian Shen, Li Ma, Denglu Hou Mar 2018

Nanostructural Origin Of Semiconductivity And Large Magnetoresistance In Epitaxial Nico2O4/Al2O3 Thin Films, Congmian Zhen, Xiaozhe Zhang, Wengang Wei, Wenzhe Guo, Ankit Pant, Xiaoshan Xu, Jian Shen, Li Ma, Denglu Hou

Xiaoshan Xu Papers

Despite low resistivity (~1 mΩ cm), metallic electrical transport has not been commonly observed in inverse spinel NiCo2O4, except in certain epitaxial thin films. Previous studies have stressed the effect of valence mixing and the degree of spinel inversion on the electrical conduction of NiCo2O4 films. In this work, we studied the effect of nanostructural disorder by comparing the NiCo2O4 epitaxial films grown on MgAl2O4 (1 1 1) and on Al2O3 (0 0 1) substrates. Although the optimal growth conditions are similar for the NiCo ...


Honeycomb Lattice Na2iro3 At High Pressures: A Robust Spin-Orbit Mott Insulator, Xiaoxiang Xi, Xiangyan Bo, X. S. Xu, P. P. Kong, Z. Liu, X. G. Hong, C. Q. Jin, G. Cao, Xiangang Wan, G. L. Carr Jan 2018

Honeycomb Lattice Na2iro3 At High Pressures: A Robust Spin-Orbit Mott Insulator, Xiaoxiang Xi, Xiangyan Bo, X. S. Xu, P. P. Kong, Z. Liu, X. G. Hong, C. Q. Jin, G. Cao, Xiangang Wan, G. L. Carr

Xiaoshan Xu Papers

The honeycomb iridate Na2IrO3 has received much attention as a candidate to realize a quantum spin liquid state, but the nature of its insulating state remains controversial. We found that the material exhibits structural transitions at 3 and 10 GPa. The former is accompanied by 166-meV suppression of the activation gap, but the energies for the low-lying interband transitions change by less than 10 meV. This can be reconciled in a picture in which the application of high pressure barely shifts the electronic bands, but rather merely broadens them. First-principles calculations uncover a strong correlation between the ...


Tuning The Neel Temperature Of Hexagonal Ferrites By Structural Distortion, Kishan Sinha, Haohan Wang, Xiao Wang, Liying Zhou, Yuewei Yin, Wenbin Wang, Xuemei Cheng, David J. Keavney, Huibo Cao, Yaohua Liu, Xifan Wu, Xiaoshan Xu Jan 2018

Tuning The Neel Temperature Of Hexagonal Ferrites By Structural Distortion, Kishan Sinha, Haohan Wang, Xiao Wang, Liying Zhou, Yuewei Yin, Wenbin Wang, Xuemei Cheng, David J. Keavney, Huibo Cao, Yaohua Liu, Xifan Wu, Xiaoshan Xu

Xiaoshan Xu Papers

To tune the magnetic properties of hexagonal ferrites, a family of magnetoelectric multiferroic materials, by atomic-scale structural engineering, we studied the effect of structural distortion on the magnetic ordering temperature (TN) in these materials. Using the symmetry analysis, we show that unlike most antiferromagnetic rare-earth transition-metal perovskites, a larger structural distortion leads to a higher TN in hexagonal ferrites and manganites, because the K3 structural distortion induces the three-dimensional magnetic ordering, which is forbidden in the undistorted structure by symmetry. We also revealed a nearlinear relation between TN and the tolerance factor and a power-law relation ...


A Brief Review Of Ferroelectric Control Of Magnetoresistance In Organic Spin Valves, Xiaoshan Xu Jan 2018

A Brief Review Of Ferroelectric Control Of Magnetoresistance In Organic Spin Valves, Xiaoshan Xu

Xiaoshan Xu Papers

Magnetoelectric coupling has been a trending research topic in both organic and inorganic materials and hybrids. The concept of controlling magnetism using an electric field is particularly appealing in energy efficient applications. In this spirit, ferroelectricity has been introduced to organic spin valves to manipulate the magneto transport, where the spin transport through the ferromagnet/organic spacer interfaces (spinterface) are under intensive study. The ferroelectric materials in the organic spin valves provide a knob to vary the interfacial energy alignment and the interfacial crystal structures, both are critical for the spin transport. In this review, we introduce the recent efforts ...


Structural And Electronic Origin Of The Magnetic Structures In Hexagonal Lufeo3, Hongwei Wang, Igor V. Solovyev, Wenbin Wang, Xiao Wang, Philip J. Ryan, David J. Keavney, Jong-Woo Kim, Thomas Z. Ward, Leyi Zhu, Jian Shen, X. M. Cheng, Lixin He, Xiaoshan Xu, Xifan Wu Jan 2014

Structural And Electronic Origin Of The Magnetic Structures In Hexagonal Lufeo3, Hongwei Wang, Igor V. Solovyev, Wenbin Wang, Xiao Wang, Philip J. Ryan, David J. Keavney, Jong-Woo Kim, Thomas Z. Ward, Leyi Zhu, Jian Shen, X. M. Cheng, Lixin He, Xiaoshan Xu, Xifan Wu

Xiaoshan Xu Papers

Using combined theoretical and experimental approaches, we studied the structural and electronic origin of the magnetic structure in hexagonal LuFeO3. Besides showing the strong exchange coupling that is consistent with the high magnetic ordering temperature, the previously observed spin reorientation transition is explained by the theoretically calculated magnetic phase diagram. The structural origin of this spin reorientation that is responsible for the appearance of spontaneous magnetization, is identified by theory and verified by x-ray diffraction and absorption experiments.


Active Control Of Magnetoresistance Of Organic Spin Valves Using Ferroelectricity, Dali Sun, Mei Fang, Xiaoshan Xu, Lu Jiang, Hangwen Guo, Yanmei Wang, Wenting Yang, Lifeng Yin, Paul C. Snijders, T. Z. Ward, Zheng Gai, X. -G. Zhang, Ho Nyung Lee, Jian Shen Jan 2014

Active Control Of Magnetoresistance Of Organic Spin Valves Using Ferroelectricity, Dali Sun, Mei Fang, Xiaoshan Xu, Lu Jiang, Hangwen Guo, Yanmei Wang, Wenting Yang, Lifeng Yin, Paul C. Snijders, T. Z. Ward, Zheng Gai, X. -G. Zhang, Ho Nyung Lee, Jian Shen

Xiaoshan Xu Papers

Organic spintronic devices have been appealing because of the long spin lifetime of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance. Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer: the magnetoresistance of the spin valve depends strongly on the history of the bias voltage ...


Multiferroic Hexagonal Ferrites (H-Rfeo3, R=Y, Dy-Lu): An Experimental Review, Xiaoshan Xu, Wenbin Wang Jan 2014

Multiferroic Hexagonal Ferrites (H-Rfeo3, R=Y, Dy-Lu): An Experimental Review, Xiaoshan Xu, Wenbin Wang

Xiaoshan Xu Papers

Hexagonal ferrites (h-RFeO3, R=Y, Dy-Lu) have recently been identified as a new family of multiferroic complex oxides. The coexisting spontaneous electric and magnetic polarizations make h-RFeO3 rare-case ferroelectric ferromagnets at low temperature. Plus the room-temperature mul- tiferroicity and predicted magnetoelectric effect, h-RFeO3 are promising materials for multiferroic applications. Here we review the structural, ferroelectric, magnetic, and magnetoelectric properties of h-RFeO3. The thin film growth is also discussed because it is critical in making high quality single crystalline materials for studying intrinsic properties.


Growth Diagram Of La0.7sr0.3mno3 Thin Films Using Pulsed Laser Deposition, Hangwen Guo, Dali Sun, Wenbin Wang, Zheng Gai, Ivan Kravchenko, Jian Shao, Lu Jiang, Thomas Z. Ward, Paul C. Snijders, Lifeng Yin, Jian Shao, Xiaoshan Xu Jan 2013

Growth Diagram Of La0.7sr0.3mno3 Thin Films Using Pulsed Laser Deposition, Hangwen Guo, Dali Sun, Wenbin Wang, Zheng Gai, Ivan Kravchenko, Jian Shao, Lu Jiang, Thomas Z. Ward, Paul C. Snijders, Lifeng Yin, Jian Shao, Xiaoshan Xu

Xiaoshan Xu Papers

An experimental study was conducted on controlling the growth mode of La0.7Sr0.3MnO3 thin films on SrTiO3 substrates using pulsed laser deposition (PLD) by tuning growth temperature, pressure, and laser fluence. Different thin film morphology, crystallinity, and stoichiometry have been observed depending on growth parameters. To understand the microscopic origin, the adatom nucleation, step advance processes, and their relationship to film growth were theoretically analyzed and a growth diagram was constructed. Three boundaries between highly and poorly crystallized growth, 2D and 3D growth, stoichiometric and non-stoichiometric growth were identified in the growth diagram ...


Room-Temperature Multiferroic Hexagonal Lufeo3 Films, Wenbin Wang, Jun Zhao, Wenbo Wang, Zheng Gai, Nina Balke, Miaofang Chi, Ho Nyung Lee, Wei Tian, Leyi Zhu, Xuemei Cheng, David J. Keavney, Jieyu Yi, Thomas Z. Ward, Paul C. Snijders, Hans M. Christen, Weida Wu, Jian Shen, Xiaoshan Xu Jan 2013

Room-Temperature Multiferroic Hexagonal Lufeo3 Films, Wenbin Wang, Jun Zhao, Wenbo Wang, Zheng Gai, Nina Balke, Miaofang Chi, Ho Nyung Lee, Wei Tian, Leyi Zhu, Xuemei Cheng, David J. Keavney, Jieyu Yi, Thomas Z. Ward, Paul C. Snijders, Hans M. Christen, Weida Wu, Jian Shen, Xiaoshan Xu

Xiaoshan Xu Papers

The crystal and magnetic structures of single-crystalline hexagonal LuFeO3 films have been studied using x-ray, electron, and neutron diffraction methods. The polar structure of these films are found to persist up to 1050 K; and the switchability of the polar behavior is observed at room temperature, indicating ferroelectricity. An antiferromagnetic order was shown to occur below 440 K, followed by a spin reorientation resulting in a weak ferromagnetic order below 130 K. This observation of coexisting multiple ferroic orders demonstrates that hexagonal LuFeO3 films are room-temperature multiferroics.


Stacking Principle And Magic Sizes Of Transition Metal Nanoclusters Based On Generalized Wulff Construction, S. F. Li, X. J. Zhao, X. S. Xu, Y. F. Gao, Zhenyu Zhang Jan 2013

Stacking Principle And Magic Sizes Of Transition Metal Nanoclusters Based On Generalized Wulff Construction, S. F. Li, X. J. Zhao, X. S. Xu, Y. F. Gao, Zhenyu Zhang

Xiaoshan Xu Papers

Nanoclusters with extra stability at certain cluster sizes are known as magic clusters with exotic properties. The classic Wulff construction principle, which stipulates that the preferred structure of a cluster should minimize its total surface energy, is often invoked in determining the cluster magicity, resulting in close-shelled Mackay icosahedronal clusters with odd-numbered magic sizes of 13, 55, 147, etc. Here we use transition metal clusters around size 55 as prototypical examples to demonstrate that, in the nanometer regime, the classic Wulff construction principle needs to be generalized to primarily emphasize the edge atom effect instead of the surface energy. Specifically ...


Infrared Phonon Modes In Multiferroic Single-Crystal Fete2o5br, K. H. Miller, X. S. Xu, H. Berger, V. Cracium, Xiaoxiang Xi, C. Martin, G. L. Carr, D. B. Tanner Jan 2013

Infrared Phonon Modes In Multiferroic Single-Crystal Fete2o5br, K. H. Miller, X. S. Xu, H. Berger, V. Cracium, Xiaoxiang Xi, C. Martin, G. L. Carr, D. B. Tanner

Xiaoshan Xu Papers

Reflection and transmission as a function of temperature (7–300 K and 5–300 K respectively) have been measured on single crystals of the multiferroic compound FeTe2O5Br utilizing light spanning from the far infrared to the visible. The complex dielectric function and other optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. Analysis of the anisotropic excitation spectra via Drude-Lorentz fitting and lattice dynamical calculations have led to the observation of 43 of the 53 modes predicted along the b axis of the monoclinic cell. The phonon response parallel to the ...


Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu Jan 2012

Crystal Field Splitting And Optical Bandgap Of Hexagonal Lufeo3 Films, Wenbin Wang, Hongwei Wang, Xiaoying Xu, Leyi Zhu, Lixin He, Elizabeth Wills, Xuemei Cheng, David J. Keavney, Jian Shen, Xifan Wu, Xiaoshan Xu

Xiaoshan Xu Papers

Hexagonal LuFeO3 films have been studied using x-ray absorption and optical spectroscopy. The crystal splitting of Fe3+ is extracted as Ee' - Ee" = 0.7 eV and Ea'1 - Ee' = 0.9 eV, and a 2.0 eV optical bandgap is determined assuming a direct gap. First-principles calculations confirm the experiments that the relative energies of crystal field splitting states do follow Ea'1 > Ee' > Ee" with slightly underestimated values and a bandgap of 1.35 eV.


Growth Diagram And Magnetic Properties Of Hexagonal Lufe2o4 Thin Films, Wenbin Wang, Zheng Gai, Miaofang Chi, Jason D. Fowlkes, Jieyu Yi, Leyi Zhu, Xuemei Cheng, David J. Keavney, Paul C. Snijders, Thomas Z. Ward, Jian Shen, Xiaoshan Xu Jan 2012

Growth Diagram And Magnetic Properties Of Hexagonal Lufe2o4 Thin Films, Wenbin Wang, Zheng Gai, Miaofang Chi, Jason D. Fowlkes, Jieyu Yi, Leyi Zhu, Xuemei Cheng, David J. Keavney, Paul C. Snijders, Thomas Z. Ward, Jian Shen, Xiaoshan Xu

Xiaoshan Xu Papers

Agrowth diagram of Lu-Fe-O compounds on MgO (111) substrates using pulsed laser deposition is constructed based on extensive growth experiments. The LuFe2O4 phase can only be grown in a small range of temperature and O2 pressure conditions. An understanding of the growth mechanism of Lu-Fe-O compound films is offered in terms of the thermochemistry at the surface. Superparamagnetism is observed in the LuFe2O4 film and is explained in terms of the effect of the impurity hexagonal LuFeO3 (h-LuFeO3) phase and structural defects.


Metastability Of Free Cobalt And Iron Clusters: A Possible Precursor To Bulk Ferromagnetism, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Anthony Liang, John Bowlan, Walt A. De Heer Jan 2011

Metastability Of Free Cobalt And Iron Clusters: A Possible Precursor To Bulk Ferromagnetism, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Anthony Liang, John Bowlan, Walt A. De Heer

Xiaoshan Xu Papers

Homonuclear cobalt and iron clusters CoN and FeN measured in a cryogenic molecular beam exist in two states with distinct magnetic moments (μ), polarizabilities, and ionization potentials, indicating distinct valences. The μ is approximately quantized: μN ~ 2B in the ground states and μN* ~ NμB in the excited states for Co; μN ~ 3N μB and μN * ~ B for Fe. At a large size, the average μ of the two states converges to the bulk value with diminishing ionization potential differences. The experiments suggest localized ferromagnetism in the two ...


Tunable Band Gap In Bi(Fe1−Xmnx)O3 Films, X. S. Xu, J. F. Ihlefeld, J. H. Lee, O. K. Ezekoye, E. Vlahos, R. Ramesh, V. Gopalan, X. Q. Pan, D. G. Schlom, J. L. Musfeldt Jan 2010

Tunable Band Gap In Bi(Fe1−Xmnx)O3 Films, X. S. Xu, J. F. Ihlefeld, J. H. Lee, O. K. Ezekoye, E. Vlahos, R. Ramesh, V. Gopalan, X. Q. Pan, D. G. Schlom, J. L. Musfeldt

Xiaoshan Xu Papers

In order to investigate band gap tunability in polar oxides, we measured the optical properties of a series of Bi(Fe1−xMnx)O3 thin films. The absorption response of the mixed metal solid solutions is approximately a linear combination of the characteristics of the two end members, a result that demonstrates straightforward band gap tunability in this system.


Optical Properties Of Quasi-Tetragonal Bifeo3 Thin Films, P. Chen, N. J. Podraza, X. S. Xu, A. Melville, E. Vlahos, V. Gopalan, R. Ramesh, D. G. Schlom, J. L. Musfeldt Jan 2010

Optical Properties Of Quasi-Tetragonal Bifeo3 Thin Films, P. Chen, N. J. Podraza, X. S. Xu, A. Melville, E. Vlahos, V. Gopalan, R. Ramesh, D. G. Schlom, J. L. Musfeldt

Xiaoshan Xu Papers

Optical transmission spectroscopy and spectroscopic ellipsometry were used to extract the optical properties of an epitaxially grown quasi-tetragonal BiFeO3 thin film in the near infrared to near ultraviolet range. The absorption spectrum is overall blue shifted compared with that of rhombohedral BiFeO3, with an absorption onset near 2.25 eV, a direct 3.1 eV band gap, and charge transfer excitations that are ~0.4 eV higher than those of the rhombohedral counterpart. We interpret these results in terms of structural strain and local symmetry breaking.


Magnetodielectric Coupling Of Infrared Phonons In Single-Crystal Cu2oseo3, K. H. Miller, X. S. Xu, H. Berger, E. S. Knowles, D. J. Arenas, M. W. Meisel, D. B. Tanner Jan 2010

Magnetodielectric Coupling Of Infrared Phonons In Single-Crystal Cu2oseo3, K. H. Miller, X. S. Xu, H. Berger, E. S. Knowles, D. J. Arenas, M. W. Meisel, D. B. Tanner

Xiaoshan Xu Papers

Reflection and transmission as a function of temperature (5–300 K) have been measured on a single crystal of the magnetoelectric ferrimagnetic compound Cu2OSeO3 utilizing light spanning the far infrared to the visible portions of the electromagnetic spectrum. The complex dielectric function and optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. The fits of the infrared phonons show a magnetodielectric effect near the transition temperature (Tc~60 K). Assignments to strong far-infrared phonon modes have been made, especially those exhibiting anomalous behavior around the transition temperature.


Adsorption-Controlled Growth Of Bimno3 Films By Molecular-Beam Epitaxy, J. H. Lee, X. Ke, R. Misra, J. F. Ihlefeld, X. S. Xu, Z. G. Mei, T. Heeg, M. Roeckerath, J. Schubert, Z. K. Liu, J. L. Musfeldt, P. Schiffer, D. G. Schlom Jan 2010

Adsorption-Controlled Growth Of Bimno3 Films By Molecular-Beam Epitaxy, J. H. Lee, X. Ke, R. Misra, J. F. Ihlefeld, X. S. Xu, Z. G. Mei, T. Heeg, M. Roeckerath, J. Schubert, Z. K. Liu, J. L. Musfeldt, P. Schiffer, D. G. Schlom

Xiaoshan Xu Papers

We have developed the means to grow BiMnO3 thin films with unparalleled structural perfection by reactive molecular-beam epitaxy and determined its band gap. Film growth occurs in an adsorption-controlled growth regime. Within this growth window bounded by oxygen pressure and substrate temperature at a fixed bismuth overpressure, single-phase films of the metastable perovskite BiMnO3 may be grown by epitaxial stabilization. X-ray diffraction reveals phase-pure and epitaxial films with w rocking curve full width at half maximum values as narrow as 11 arc sec (0.003°). Optical absorption measurements reveal that BiMnO3 has a direct band gap of ...


Lattice Dynamical Probe Of Charge Order And Antipolar Bilayer Stacking In Lufe2o4, X. S. Xu, J. De Groot, Q.-C. Sun, B. C. Sales, D. Mandrus, M. Angst, A. P. Litvinchuk, J. L. Musfeldt Jan 2010

Lattice Dynamical Probe Of Charge Order And Antipolar Bilayer Stacking In Lufe2o4, X. S. Xu, J. De Groot, Q.-C. Sun, B. C. Sales, D. Mandrus, M. Angst, A. P. Litvinchuk, J. L. Musfeldt

Xiaoshan Xu Papers

We investigated the infrared response of LuFe2O4 through the series of charge, magnetic, and structural transitions. All vibrational modes couple strongly to the charge order, whereas the LuO zone-folding modes are also sensitive to magnetic order and structural distortion. The dramatic splitting of the LuO2 layer mode is attributed to charge-rich/poor proximity effects and its temperature dependence reveals the antipolar nature of the W layer pattern.


Absence Of Spin Liquid Behavior In Nd3ga5sio14 Using Magneto-Optical Spectroscopy, X. S. Xu, T. V. Brinzari, S. Mcgill, H. D. Zhou, C. R. Wiebe, J. L. Musfeldt Jan 2009

Absence Of Spin Liquid Behavior In Nd3ga5sio14 Using Magneto-Optical Spectroscopy, X. S. Xu, T. V. Brinzari, S. Mcgill, H. D. Zhou, C. R. Wiebe, J. L. Musfeldt

Xiaoshan Xu Papers

We measured the low-lying crystal field levels of Nd3+ in Nd3Ga5SiO14 via magneto-optical spectroscopy and employed the extracted energies, magnetic moments, and symmetries to analyze the magnetic properties and test the spin liquid candidacy of this material. The exchange interaction is surprisingly small, a discovery that places severe constraints on models used to describe the ground state of this system. Further, it demonstrates the value of local-probe photophysical techniques for rare-earthcontaining materials where bulk property measurements can be skewed by low-lying electronic structure.


Optical Properties And Magnetochromism In Multiferroic Bifeo3, X. S. Xu, T. V. Brinzari, S. Lee, Y. H. Chu, L. W. Martin, A. Kumar, S. Mcgill, R. C. Rai, R. Ramesh, V. Gopalan, S. W. Cheong, J. L. Musfeldt Jan 2009

Optical Properties And Magnetochromism In Multiferroic Bifeo3, X. S. Xu, T. V. Brinzari, S. Lee, Y. H. Chu, L. W. Martin, A. Kumar, S. Mcgill, R. C. Rai, R. Ramesh, V. Gopalan, S. W. Cheong, J. L. Musfeldt

Xiaoshan Xu Papers

In order to investigate spin-charge coupling in multiferroic oxides, we measured the optical properties of BiFeO3. Although the direct 300 K charge gap is observed at 2.67 eV, absorption onset actually occurs at much lower energy with Fe3+ excitations at 1.41 and 1.90 eV. Temperature and magnetic-field-induced spectral changes reveal complex interactions between on-site crystal-field and magnetic excitations in the form of magnon sidebands. We employ the sensitivity of these magnon sidebands to map out the magnetic-fieldtemperature phase diagram which demonstrates optical evidence for spin spiral quenching above 20 T and suggests a spin domain ...


Magnon Sidebands And Spin-Charge Coupling In Bismuth Ferrite Probed By Nonlinear Optical Spectroscopy, M. O. Ramirez, A. Kumar, S. A. Denev, N. J. Podraza, X. S. Xu, R. C. Rai, Y. H. Chu, J. Seidel, L. W. Martin, S. -Y. Yang, E. Saiz, J. F. Ihlefeld, S. Lee, J. Klug, S. W. Cheong, M. J. Bedzyk, O. Auciello, D. G. Schlom, R. Ramesh, J. Orenstein, J. L. Musfeldt, V. Gopalan Jan 2009

Magnon Sidebands And Spin-Charge Coupling In Bismuth Ferrite Probed By Nonlinear Optical Spectroscopy, M. O. Ramirez, A. Kumar, S. A. Denev, N. J. Podraza, X. S. Xu, R. C. Rai, Y. H. Chu, J. Seidel, L. W. Martin, S. -Y. Yang, E. Saiz, J. F. Ihlefeld, S. Lee, J. Klug, S. W. Cheong, M. J. Bedzyk, O. Auciello, D. G. Schlom, R. Ramesh, J. Orenstein, J. L. Musfeldt, V. Gopalan

Xiaoshan Xu Papers

The interplay between spin waves (magnons) and electronic structure in materials leads to the creation of additional bands associated with electronic energy levels which are called magnon sidebands. The large difference in the energy scales between magnons (meV) and electronic levels (eV) makes this direct interaction weak and hence makes magnon sidebands difficult to probe. Linear light absorption and scattering techniques at low temperatures are traditionally used to probe these sidebands. Here we show that optical secondharmonic generation, as the lowest-order nonlinear process, can successfully probe the magnon sidebands at room temperature and up to 723 K in bismuth ferrite ...


Charge Order, Dynamics, And Magnetostructural Transition In Multiferroic Lufe2o4, X. S. Xu, M. Angst, T. V. Brinzari, R. P. Hermann, J. L. Musfeldt, A. D. Christianson, D. Mandrus, B. C. Sales, S. Mcgill, J. -W. Kim, Z. Islam Jan 2008

Charge Order, Dynamics, And Magnetostructural Transition In Multiferroic Lufe2o4, X. S. Xu, M. Angst, T. V. Brinzari, R. P. Hermann, J. L. Musfeldt, A. D. Christianson, D. Mandrus, B. C. Sales, S. Mcgill, J. -W. Kim, Z. Islam

Xiaoshan Xu Papers

We investigated the series of temperature and field-driven transitions in LuFe2O4 by optical and Mossbauer spectroscopies, magnetization, and x-ray scattering in order to understand the interplay between charge, structure, and magnetism in this multiferroic material. We demonstrate that charge fluctuation has an onset well below the charge ordering transition, supporting the ‘‘order by fluctuation’’ mechanism for the development of charge order superstructure. Bragg splitting and large magneto-optical contrast suggest a low-temperature monoclinic distortion that can be driven by both temperature and magnetic field.


Optical Band Gap Of Bifeo3 Grown By Molecular-Beam Epitaxy, J. F. Ihlefeld, N. J. Podraza, Z. K. Liu, R. C. Rai, X. Xu, T. Heeg, Y. B. Chen, J. Li, R. W. Collins, J. L. Musfeldt, X. Q. Pan, J. Schubert, R. Ramesh, D. G. Schlom Jan 2008

Optical Band Gap Of Bifeo3 Grown By Molecular-Beam Epitaxy, J. F. Ihlefeld, N. J. Podraza, Z. K. Liu, R. C. Rai, X. Xu, T. Heeg, Y. B. Chen, J. Li, R. W. Collins, J. L. Musfeldt, X. Q. Pan, J. Schubert, R. Ramesh, D. G. Schlom

Xiaoshan Xu Papers

BiFeO3 thin films have been deposited on (001) SrTiO3 substrates by adsorption-controlled reactive molecular-beam epitaxy. For a given bismuth overpressure and oxygen activity, single-phase BiFeO3 films can be grown over a range of deposition temperatures in accordance with thermodynamic calculations. Four-circle x-ray diffraction reveals phase-pure, epitaxial films with w rocking curve full width at half maximum values as narrow as 29 arc sec (0.008°). Multiple-angle spectroscopic ellipsometry reveals a direct optical band gap at 2.74 eV for stoichiometric as well as 5% bismuth-deficient single-phase BiFeO3 films.


Photoconductivity In Bifeo3 Thin Films, S. R. Basu, L. W. Martin, Y. H. Chu, M. Gajek, R. Ramesh, R. C. Rai, X. S. Xu, J. L. Musfeldt Jan 2008

Photoconductivity In Bifeo3 Thin Films, S. R. Basu, L. W. Martin, Y. H. Chu, M. Gajek, R. Ramesh, R. C. Rai, X. S. Xu, J. L. Musfeldt

Xiaoshan Xu Papers

The optical properties of epitaxial BiFeO3 thin films have been characterized in the visible range. Variable temperature spectra show an absorption onset near 2.17 eV, a direct gap (2.667±0.005 eV at 300 K), and charge transfer excitations at higher energy. Additionally, we report photoconductivity in BiFeO3 films under illumination from a 100 mW/cm2 white light source. A direct correlation is observed between the magnitude of the photoconductivity and postgrowth cooling pressure. Dark conductivities increased by an order of magnitude when comparing films cooled in 760 and 0.1 Torr. Large increases in ...


Magnetic Enhancement In Cobalt-Manganese Alloy Clusters, Shuangye Yin, Ramiro Moro, Xiaoshan Xu, Walter A. De Heer Jan 2007

Magnetic Enhancement In Cobalt-Manganese Alloy Clusters, Shuangye Yin, Ramiro Moro, Xiaoshan Xu, Walter A. De Heer

Xiaoshan Xu Papers

Magnetic moments of CoNMnM and CoNVM clusters (N ≤ 60; M ≤ N/3) are measured in molecular beams using the Stern-Gerlach deflection method. Surprisingly, the per atom average moments of CoNMnM clusters are found to increase with Mn concentration, in contrast to bulk CoMn. The enhancement with Mn doping is found to be independent of cluster size and composition in the size range studied. Meanwhile, CoNVM clusters show reduction of average moments with increasing V doping, consistent with what is expected in bulk CoV. The results are discussed within ...


Magnetic Moments And Adiabatic Magnetization Of Free Cobalt Clusters, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Walt A. De Heer Jan 2005

Magnetic Moments And Adiabatic Magnetization Of Free Cobalt Clusters, Xiaoshan Xu, Shuangye Yin, Ramiro Moro, Walt A. De Heer

Xiaoshan Xu Papers

Magnetizations and magnetic moments of free cobalt clusters CoN (12< N <200) in a cryogenic (25 K ≤ T ≤ 100 K) molecular beam were determined from Stern-Gerlach deflections. All clusters preferentially deflect in the direction of the increasing field and the average magnetization resembles the Langevin function for all cluster sizes even at low temperatures. We demonstrate in the avoided crossing model that the average magnetization may result from adiabatic processes of rotating and vibrating clusters in the magnetic field and that spin relaxation is not involved. This resolves a longstanding problem in the interpretation of cluster beam deflection experiments with implications for nanomagnetic systems in general.


Measurement Of Magnetic Moments Of Free BiNMnM Clusters, Shuangye Yin, Xiaoshan Xu, Ramiro Moro, Walt A. De Heer Jan 2005

Measurement Of Magnetic Moments Of Free BiNMnM Clusters, Shuangye Yin, Xiaoshan Xu, Ramiro Moro, Walt A. De Heer

Xiaoshan Xu Papers

Magnetic properties of free BiNMnM clusters (N=2–20, M=0–7) are determined from Stern-Gerlach deflections at low temperature (46.5 K). Pure bismuth clusters with odd number of atoms exhibit paramagnetic deflections. The addition of manganese atoms produces a ferromagnetic response which is strongly size dependent. Certain combinations have very large magnetic moments such as Bi5Mn3, Bi9 Mn4, Bi10Mn5, and Bi12Mn6.