2,644 research outputs found
3d-electron Heisenberg pyrochlore Mn2Sb2O7
No full textIn frustrated magnetic systems, geometric constraints or the competition among interactions introduce extremely high degeneracy and prevent the system from readily selecting a low-temperature ground state. The most frustrated known spin arrangement is on the pyrochlore lattice, but nearly all magnetic pyrochlores have unquenched orbital angular momenta, constraining the spin directions through spin-orbit coupling. Pyrochlore Mn2Sb2O7 is an extremely rare Heisenberg pyrochlore system with directionally unconstrained spins and low chemical disorder. We show that it undergoes a spin-glass transition at 5.5 K, which is suppressed by disorder arising from Mn vacancies, indicating this ground state to be a direct consequence of the spins’ interactions. The striking similarities to 3d transition-metal pyrochlores with unquenched angular momenta suggests that the low spin-orbit coupling in the 3d block makes Heisenberg pyrochlores far more accessible than previously imagined. ©2016 American Physical Society1431sciescopu
Studies on the high-temperature ferroelectric transition of multiferroic hexagonal manganite RMnO3
No full textHexagonal manganites are multiferroic materials with two highly-dissimilar phase transitions: a ferroelectric transition (from P63/mmc to P63cm) at a temperature higher than 1000 K and an antiferromagnetic transition at T N = 65-130 K. Despite its critical relevance to the intriguing ferroelectric domain physics, the details of the ferroelectric transition are not well known to date primarily because of the ultra-high transition temperature. Using high-temperature x-ray diffraction experiments, we show that the ferroelectric transition is a single transition of abrupt order and R-Op displacement is the primary order parameter. This structural transition is then simultaneously accompanied by MnO5 tilting and the subsequent development of electric polarization. © 2018 IOP Publishing Ltd1
Doping effects on the ferroelectric transition of multiferroic Y(Mn,Al/Ga) O3
No full textMultiferroic hexagonal manganites RMnO3 have a very high ferroelectric transition temperature around and above 1200 K, depending on the rare-earth elements, and a reasonably large electric polarization of about 5.5μC/cm2 at room temperature. It is generally believed that the ferroelectric transition is driven by the combination of R-OP displacement and MnO5 tilting, and hence called improper ferroelectric. In order to better understand the improper ferroelectric transition, we studied doping effects, using two elements with the same valence but a different ionic size: Al and Ga on the Mn site of YMnO3. Through detailed structural studies and nanoscale measurements of piezoresponse force microscopy (PFM) we conclude that there is a drastic doping effect for Al, whose ionic size is much smaller than Mn. It is in stark contrast with our observation that Ga, having a slightly smaller ionic size with Mn, does not change the ferroelectric transition up to 50% doping. This drastic difference in the doping effect is due to local strain induced by the difference in the ionic size of Al and Mn as compared with that of Mn, and sheds light on the intriguing nature of the improper ferroelectric transition. © 2018 American Physical Societ
Terahertz absorption spectroscopy study of spin waves in orthoferrite YFeO3 in a magnetic field
No full textWe measured absorption of THz radiation in YFeO3 single crystals at a temperature of 3 K in the magnetic field up to 17 T applied in all three crystallographic directions. Two spin-wave modes were observed at the �� point with energies 1.2 meV (9.8 cm-1) and 2.4 meV (19.3 cm-1) in zero field. From the magnetic-field dependence of mode energies, we have refined the previously proposed model [S. E. Hahn, Phys. Rev. B 89, 014420 (2014)PRBMDO1098-012110.1103/PhysRevB.89.014420] and quantified the parameters of Dzyaloshinskii-Moriya interactions and single-ion anisotropies. ? 2018 authors. Published by the American Physical Societ
Low Temperature Measurement of the Electrical Conductivity in Amorphous InGaZnO Thin Films
No full textWe examine the temperature-dependent electrical conductivity in amorphous InGaZnO thin films with various cation compositions. In-rich films are metallic, while Ga-rich films are semiconducting with logarithmic conductivities linear to -T−1/4 above T = 60 K. The Zn-rich films are also semiconducting but have >102 times higher conductivity than the Ga-rich films. At T > 60 K, thermal electronic excitation dominantly contributes the conduction, while at T < 60 K, certain impurity scatterings or structural disorders have importance in the electrical properties in low carrier a-IGZO system.3311sciescopu
Antiferromagnetic ordering in Li2MnO3 single crystals with a two-dimensional honeycomb lattice
No full textLi 2MnO 3 consists of a layered Mn honeycomb lattice separated by a single layer of LiO 6 octahedra along the c-axis. By using single crystal Li 2MnO 3 samples, we have examined the physical properties and carried out both powder and single crystal neutron diffraction studies to determine that Mn moments order antiferromagnetically at T N=36K with an ordered magnetic moment of 2.3μ B perpendicular to the ab plane. We have also discovered that about 35% of the full magnetic entropy is released in the supposedly simple paramagnetic phase, indicative of unusual spin dynamics at higher temperature. © 2012 IOP Publishing Ltd.115131sciescopu
Hexagonal RMnO3: a model system for two-dimensional triangular lattice antiferromagnets
No full textThe hexagonal RMnO3(h-RMnO3) are multiferroic materials, which exhibit the coexistence of a magnetic order and ferroelectricity. Their distinction is in their geometry that both results in an unusual mechanism to break inversion symmetry and also produces a two-dimensional triangular lattice of Mn spins, which is subject to geometrical magnetic frustration due to the antiferromagnetic interactions between nearest-neighbor Mn ions. This unique combination makes the h-RMnO3 a model system to test ideas of spin-lattice coupling, particularly when both the improper ferroelectricity and the Mn trimerization that appears to determine the symmetry of the magnetic structure arise from the same structure distortion. In this review we demonstrate how the use of both neutron and X-ray diffraction and inelastic neutron scattering techniques have been essential to paint this comprehensive and coherent picture of h-RMnO3. (c) 2016 International Union of Crystallography110111scopu
Frustrated antiferromagnetic honeycomb-tunnel-like lattice<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Cu</mml:mi><mml:msub><mml:mi>R</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Ge</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>8</mml:mn></mml:msub></mml:mrow></mml:math>(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>R</mml:mi><mml:mo>=</mml:mo><mml:mi>Pr</mml:mi></mml:mrow></mml:math>, Nd, Sm, and Eu)
No full textNew frustrated antiferromagnetic compounds CuR2Ge2O8 (R=Pr, Nd, Sm, Eu) have been investigated using high-resolution x-ray diffraction, magnetic, and heat capacity measurements. These systems show different magnetic lattices depending on rare-earth element. The nonmagnetic Eu compound is a S=1/2 two-dimensional triangular antiferromagnetic lattice oriented in the ac plane with geometrical frustration. On the other hand, the Pr, Nd, and Sm compounds show a three-dimensional honeycomb-tunnel-like lattice made of R3+ running along the a axis with the characteristic behavior of frustrated antiferromagnets. © 2017 American Physical Society101sciescopu
Coexisting Z-type charge and bond order in metallic NaRu2O4
No full text© 2022, The Author(s).How particular bonds form in quantum materials has been a long-standing puzzle. Two key concepts dealing with charge degrees of freedom are dimerization (forming metal-metal bonds) and charge ordering. Since the 1930s, these two concepts have been frequently invoked to explain numerous exciting quantum materials, typically insulators. Here we report dimerization and charge ordering within the dimers coexisting in metallic NaRu2O4. By combining high-resolution x-ray diffraction studies and theoretical calculations, we demonstrate that this unique phenomenon occurs through a new type of bonding, which we call Z-type ordering. The low-temperature superstructure has strong dimerization in legs of zigzag ladders, with short dimers in legs connected by short zigzag bonds, forming Z-shape clusters: simultaneously, site-centered charge ordering also appears. Our results demonstrate the yet unknown flexibility of quantum materials with the intricate interplay among orbital, charge, and lattice degrees of freedom.11Nscopu
Doping effects on trimerization and magnetoelectric coupling of single crystal multiferroic (Y,Lu)MnO3
No full textHexagonal RMnO3 is a multiferroic compound with a giant spin-lattice coupling at an antiferromagnetic transition temperature, Lee et al (2008 Nature 451 805). Despite extensive studies over the past two decades, the origin and underlying microscopic mechanism of strong spin-lattice coupling remain very much elusive. In this study, we have tried to address this problem by measuring the thermal expansion and dielectric constant of doped single crystals Y1-xLuxMnO3 where x = 0, 0.25, 0.5, 0.75, and 1.0. From these measurements, we confirm that there is a progressive change in the physical properties with doping. At the same time, all our samples exhibit clear anomalies at T N, even in the samples where x = 0.5 and 0.75. This is opposed to some earlier ideas, which suggests an unusual doping dependence of the anomaly. Our work reveals yet another interesting facet of the spin-lattice coupling issue in hexagonal RMnO3. © 2017 IOP Publishing Ltd1111sciescopu
- …
