Piscataway, NJ, United States
Piscataway, NJ, United States

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Hearmon A.J.,University of Oxford | Hearmon A.J.,Diamond Light Source | Johnson R.D.,University of Oxford | Johnson R.D.,Rutherford Appleton Laboratory | And 7 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

The hexaferrites are known to exhibit a wide range of magnetic structures, some of which are connected to important technological applications and display magnetoelectric properties. We present data on the low magnetic field structures stabilized in a Y-type hexaferrite as observed by resonant soft x-ray diffraction. The helical spin block arrangement that is present in zero applied magnetic field becomes fanlike as a field is applied in plane. The propagation vectors associated with each fan structure are studied as a function of magnetic field, and a new magnetic phase is reported. Mean field calculations indicate this phase should stabilize close to the boundary of the previously reported phases. © 2013 American Physical Society.


Eom M.J.,Pohang University of Science and Technology | Kim K.,Pohang University of Science and Technology | Jo Y.J.,Kyungpook National University | Yang J.J.,Pohang University of Science and Technology | And 6 more authors.
Physical Review Letters | Year: 2014

We report a de Haas-van Alphen (dHvA) oscillation study on IrTe2 single crystals showing complex dimer formations. By comparing the angle dependence of dHvA oscillations with band structure calculations, we show distinct Fermi surface reconstruction induced by a 1=5-type and a 1=8-type dimerizations. This verifies that an intriguing quasi-two-dimensional conducting plane across the layers is induced by dimerization in both cases. A phase transition to the 1=8 phase with higher dimer density reveals that local instabilities associated with intra- and interdimer couplings are the main driving force for complex dimer formations in IrTe2. © 2014 American Physical Society.


Oh Y.S.,Rutgers Center for Emergent Materials | Yang J.J.,Pohang University of Science and Technology | Horibe Y.,Rutgers Center for Emergent Materials | Cheong S.-W.,Rutgers Center for Emergent Materials | Cheong S.-W.,Pohang University of Science and Technology
Physical Review Letters | Year: 2013

Selenium substitution drastically increases the transition temperature of iridium ditelluride (IrTe2) to a diamagnetic superstructure from 278 to 560 K. Transmission electron microscopy experiments revealed that this enhancement is accompanied by the evolution of nonsinusoidal structure modulations from q=1/5(101̄) to q=1/6(101̄) types. These comprehensive results are consistent with the concept of the destabilization of polymeric Te-Te bonds at the transition, the temperature of which is increased by chemical and hydrostatic pressure and by the substitution of Te with the more electronegative Se. This temperature-induced depolymerization transition in IrTe2 is unique in crystalline inorganic solids. © 2013 American Physical Society.


Kim H.S.,Korea Basic Science Institute | Kim H.S.,Pohang University of Science and Technology | Kim T.-H.,Pohang University of Science and Technology | Yang J.,Pohang University of Science and Technology | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We investigate atomic and electronic structures of the intriguing low-temperature phase of IrTe2 using high-resolution scanning tunneling microscopy and spectroscopy. We confirm various stripe superstructures such as ×3, ×5, and ×8. The strong vertical and lateral distortions of the lattice for the stripe structures are observed in agreement with recent calculations. The spatial modulations of electronic density of states are clearly identified as separated from the structural distortions. These structural and spectroscopic characteristics are not consistent with the charge-density wave and soliton lattice model proposed recently. Instead, we show that the Ir (Te) dimerization together with the Ir 5d charge ordering can explain these superstructures, supporting the Ir dimerization mechanism of the phase transition. © 2014 American Physical Society.


Johnson R.D.,University of Oxford | Johnson R.D.,Rutherford Appleton Laboratory | Cao K.,University of Oxford | Chapon L.C.,Laue Langevin Institute | And 7 more authors.
Physical Review Letters | Year: 2013

Structural and magnetic chiralities are found to coexist in a small group of materials in which they produce intriguing phenomenologies such as the recently discovered Skyrmion phases. Here, we describe a previously unknown manifestation of this interplay in MnSb2O6, a trigonal oxide with a chiral crystal structure. Unlike all other known cases, the MnSb2O6 magnetic structure is based on corotating cycloids rather than helices. The coupling to the structural chirality is provided by a magnetic axial vector, related to the so-called vector chirality. We show that this unique arrangement is the magnetic ground state of the symmetric-exchange Hamiltonian, based on ab initio theoretical calculations of the Heisenberg exchange interactions, and is stabilized by out-of-plane anisotropy. MnSb 2O6 is predicted to be multiferroic with a unique ferroelectric switching mechanism. © 2013 American Physical Society.


Kim H.S.,Korea Basic Science Institute | Kim H.S.,Pohang University of Science and Technology | Kim S.,Pohang University of Science and Technology | Kim S.,Harvard University | And 8 more authors.
Nano Letters | Year: 2016

Entanglement of charge orderings and other electronic orders such as superconductivity is in the core of challenging physics issues of complex materials including high temperature superconductivity. Here, we report on the observation of a unique nanometer scale honeycomb charge ordering of the cleaved IrTe2 surface, which hosts a superconducting state. IrTe2 was recently established to exhibit an intriguing cascade of stripe charge orders. The stripe phases coexist with a hexagonal phase, which is formed locally and falls into a superconducting state below 3 K. The atomic and electronic structures of the honeycomb and hexagon pattern of this phase are consistent with the charge order nature, but the superconductivity does not survive on neighboring stripe charge order domains. The present work provides an intriguing physics issue and a new direction of functionalization for two-dimensional materials. © 2016 American Chemical Society.


Kim K.,Pohang University of Science and Technology | Kim S.,Pohang University of Science and Technology | Ko K.-T.,Pohang University of Science and Technology | Ko K.-T.,Max Planck Institute for Chemical Physics of Solids | And 6 more authors.
Physical Review Letters | Year: 2015

We have explored the origin of unusual first-order-type electronic and structural transitions in IrTe2, based on the first-principles total energy density functional theory analysis. We have clarified that the structural transition occurs through the interplay among the charge density wavelike lattice modulation with q1/5 = (1/5; 0; 1/5), in-plane dimer ordering, and the uniform lattice deformation. The Ir-Ir dimer formation via a molecular-orbital version of the Jahn-Teller distortion in the Ir-Ir zigzag stripe is found to play the most important role in producing the charge disproportionation state. Angle-resolved photoemission spectroscopy reveals the characteristic features of structural transition, which are in good agreement with the density functional theory bands obtained by the band-unfolding technique. © 2015 American Physical Society.


Oh Y.S.,Seoul National University | Jeon B.-G.,Seoul National University | Haam S.Y.,Seoul National University | Park S.,Rutgers Center for Emergent Materials | And 5 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

Comparative studies of magnetoelectric susceptibility (α), magnetization (M), and magnetostriction (u) in TbMn2O5 reveal that the increment of M owing to the field-induced Tb3+ spin alignment produces a field-asymmetric line shape in the α(H) curve, which is conspicuous in a low-temperature incommensurate phase but persistently subsists in the entire ferroelectric phase. Correlations among electric polarization, u, and M2 variation represent linear relationships, unambiguously showing the significant role of Tb magnetoelastic effects on the low-field magnetoelectric phenomena of TbMn2O5. An effective free energy capturing the observed experimental features is also suggested. © 2011 American Physical Society.


Mun E.,Los Alamos National Laboratory | Mun E.,Simon Frazer University | Weickert F.,Los Alamos National Laboratory | Kim J.,Los Alamos National Laboratory | And 8 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

We investigate partially disordered antiferromagnetism in CoCl2-2SC(NH2)2, in which ab-plane hexagonal layers are staggered along the c axis rather than stacked. A robust 1/3 state forms in applied magnetic fields in which the spins are locked, varying as a function of neither temperature nor field. By contrast, in zero field and applied fields at higher temperatures, partial antiferromagnetic order occurs, in which free spins are available to create a Curie-like magnetic susceptibility. We report measurements of the crystallographic structure and the specific heat, magnetization, and electric polarization down to T=50mK and up to μ0H=60T. The Co2+S=3/2 spins are Ising-like and form distorted hexagonal layers. The Ising energy scale is well separated from the magnetic exchange, and both energy scales are accessible to the measurements, allowing us to cleanly parametrize them. In transverse fields, a quantum Ising phase transition can be observed at 2 T. Finally, we find that magnetic exchange striction induces changes in the electric polarization up to 3μC/m2, and single-ion magnetic anisotropy effects induce a much larger electric polarization change of 300μC/m2. © 2016 American Physical Society.


Johnson R.D.,University of Oxford | Johnson R.D.,Rutherford Appleton Laboratory | Barone P.,CNR Institute of Neuroscience | Bombardi A.,Diamond Light Source | And 6 more authors.
Physical Review Letters | Year: 2013

Magnetic domains at the surface of a ferroelectric monodomain BiFeO 3 single crystal have been imaged by hard x-ray magnetic scattering. Magnetic domains up to several hundred microns in size have been observed, corresponding to cycloidal modulations of the magnetization along the wave vector k=(δ,δ,0) and symmetry equivalent directions. The rotation direction of the magnetization in all magnetic domains, determined by diffraction of circularly polarized light, was found to be unique and in agreement with predictions of a combined approach based on a spin-model complemented by relativistic density-functional simulations. Imaging of the surface shows that the largest adjacent domains display a 120 vortex structure. © 2013 American Physical Society.

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