The unusual magnetoelectric effects observed in the multiferroic phase arising below TN=6.7K in Ba2CoGe2O7 (BCG) are related to the spontaneous toroidal moment existing in this compound. The transition to the multiferroic state, which involves spontaneous magnetization, polarization and toroidal moment gives rise to spontaneous toroidic effects. These effects produce specific contributions to the spontaneous polarization and magnetization under applied magnetic or electric fields which provide indirect indications of the existence and role of the toroidal moment in multiferroic materials. The toroidic contribution to the electric polarization in BCG is shown to result from single-ion effects.
Rare earth pyrochlore Iridates (RE2Ir2O7) consist of two interpenetrating cation sublattices, the RE with highly-frustrated magnetic moments, and the Iridium with extended conduction orbitals significantly mixed by spin-orbit interactions. The coexistence and coupling of these two sublattices create a landscape for discovery and manipulation of quantum phenomena such as the topological Hall effect, massless conduction bands, and quantum criticality. Thin films allow extended control of the material system via symmetry-lowering effects such as strain. While bulk Pr2Ir2O7 shows a spontaneous hys…
Electrically and magnetically induced optical rotation in Pb5Ge3O11:Cr crystals at the phase transition. 2. Faraday effect in pure and Cr-doped lead germanate in the presence of electric field and spontaneous polarization
In this work we propose an alternative model to explain the spontaneous exchange bias (SEB) effect observed in spin glass (SG)-like systems. As in a previously proposed model (Ref. 1), it is based on the unconventional dynamics of the SG-like moments at the magnetic hysteresis cycle. However, using a reliable estimate of the amount of SG-spins that are relaxing during the cycle, the new model can correctly describe the changes in the SEB observed for measurements performed at different temperatures and different maximum applied fields.
This paper investigates the size effect on the coalescence process of contacting nanoparticles. It is revealed by molecular dynamics that the nanometer-sized surface curvature coupled with the effective melting temperature exhibits a strong influence on the atom diffusion at the interface, and is therefore critical to the coalescence time. This effect is particularly pronouncing for surface curvatures below 20 nm. A phenomenological model is derived from the melting-point reduction approach to describe the kinetic process of nanowire coalescence and is validated against a variety of simulation…
La$_{1.5}$Ba$_{0.5}$CoMnO$_{6}$ is a re-entrant cluster glass material exhibiting a robust negative exchange bias (EB) effect even after being cooled from an unmagnetized state down to low temperature in zero magnetic field. Here we thoroughly investigate this phenomena by performing magnetization as a function of applied field [$M(H)$] measurements at several different temperatures and maximum applied magnetic fields ($H_m$). The spontaneous EB (SEB) effect is observed below 20 K, and shows a maximum value for $H_m$ = 75 kOe. The effect is greatly enhanced when the $M(H)$ curves are measured …
Structural, electronic and magnetic properties of polycrystalline La2-xCaxCoMnO6 (0 $\leq$ x $\leq$ 0.75) compounds are investigated by x-ray diffraction and magnetometry. All the samples have an orthorhombic structure and show a slight decrease in the unit cell with Ca-doping. Temperature-dependent magnetization measurements reveal a complex magnetic behavior with two ferromagnetic transitions. These transitions are ascribed to Co2+--Mn4+ and Co3+--Mn3+ couplings and suggest the presence of additional antiferromagnetic couplings in these disordered compounds. Field-dependent magnetization cur…
Effects of short-range electronic interactions in a three-dimensional line-node semimetal that supports linearly dispersing quasiparticles around an isolated loop in the Brillouin zone are discussed. Due to vanishing density of states ($\varrho(E) \sim |E|$) various orderings in the bulk of the system, such as the antiferromagnet and charge-density-wave, set in for sufficiently strong onsite ($U$) and nearest-neighbor ($V$) repulsions, respectively. While onset of these two orderings from the semimetallic phase takes place through continuous quantum phase transitions, a first-order transition …
Spontaneous Symmetry Breaking of Cavity Vacuum and Emergent Gyrotropic Effects in Embedded moiré Superlattices
New Cornerstone Science Lab, Department of Physics, The University of Hong Kong（香港大学新Cornerstone科学实验室物理系）；HK Institute of Quantum Science & Technology, University of Hong Kong（香港大学香港量子科学与技术研究所）；Institute of Applied Physics and Materials Engineering, University of Macau（澳门大学应用物理与材料工程研究所）
Magnetotransport and magnetism of epitaxial SmTiO3/EuTiO3 heterostructures grown by molecular beam epitaxy are investigated. It is shown that the polar discontinuity at the interface introduces ~ 3.9x10^14 cm^-2 carriers into the EuTiO3. The itinerant carriers exhibit two distinct contributions to the spontaneous Hall effect. The anomalous Hall effect appears despite a very small magnetization, indicating a non-collinear spin structure and the second contribution resembles a topological Hall effect. Qualitative differences exist in the temperature dependence of both Hall effects when compared …
Using hybrid exchange-correlation functional in ab initio density functional theory calculations, we study magnetic properties and strain effect on the electronic properties of $α$-graphyne monolayer. We find that a spontaneous antiferromagnetic (AF) ordering occurs with energy band gap ($\sim$ 0.5 eV) in the equilibrated $α$-graphyne. Bi-axial tensile strain enhances the stability of AF state as well as the staggered spin moment and value of the energy gap. The antiferromagnetic semiconductor phase is quite robust against moderate carrier filling with threshold carrier density up to 1.7$\time…
