Using a Monte Carlo (MC) method, we study an effective model for the Fe(II)Fe(III) bimetallic oxalates. Within a hybrid quantum-classical MC algorithm, the Heisenberg S=2 and $S'=5/2$ spins on the Fe(II) and Fe(III) sites are updated using a quantum MC loop while the Ising-like orbital angular momenta on the Fe(II) sites are updated using a single-spin classical MC flip. The effective field acting on the orbital angular momenta depends on the quantum state of the system. We find that the mean-field phase diagram for the model is surprisingly robust with respect to fluctuations. In particular, the region displaying two compensation points shifts and shrinks but remains finite.
Hybrid path integral Monte Carlo simulation of rigid diatomic molecules: effect of quantized rotations on the selectivity of hydrogen isotopes in carbon nanotubes
Configurations of the molecules on the wall of a vacancy, formed by removing a central and its first and second nearest-neighbor (NN) molecules in solid CO2 with the Pa3 structure, were calculated by the Monte Carlo simulation technique at T = 0, 100, and 200 K and a nominal pressure of P = 1 bar. It was found that the deviations of both the center-of-mass and the orientational coordinates of the molecules from the unperturbed coordinates had a three-fold symmetry about a body diagonal axis of the crystal. It was also found that a single CO2 molecule, initially placed in the center of the vaca…
Three-dimensional (3D) excitonic complexes influence the optoelectronic properties of bulk semiconductors. More generally, correlated few-particle molecules and ions, held together by pairwise Coulomb potentials, play a fundamental role in a variety of fields in physics and chemistry. Based on statistically exact diffusion quantum Monte Carlo calculations, we have studied excitonic three- and four-body complexes (trions and biexcitons) in bulk 3D semiconductors as well as a range of small molecules and ions in which the nuclei are treated as quantum particles on an equal footing with the elect…
The effect of surface roughness on the structure of liquid crystalline fluids near solid substrates is studied by Monte Carlo simulations. The liquid crystal is modelled as a fluid of soft ellipsoidal molecules and the substrate is modelled as a hard wall that excludes the centres of mass of the fluid molecules. Surface roughness is introduced by embedding a number of molecules with random positions and orientations within the wall. It is found that the density and order near the wall are reduced as the wall becomes rougher (i.e. the number of embedded molecules is increased). Anchoring coeffi…
Electric dipoles of water molecules, enclosed singly in regularly spaced nanopores of a cordierite crystal, become ordered at low temperature due to their mutual interaction and show the frequency dependence of their dielectric susceptibility, typical for relaxor ferroelectrics, according to recent experimental data. The corresponding phase transition is accompanied by anomalies in thermodynamic quantities, such as heat capacity and dielectric susceptibility, which are calculated here using the Monte Carlo method, and their agreement the experimental data is discussed. Despite the increase in …
Single molecular magnet (SMM) like paramagnetic molecules interacting with the ferromagnetic electrodes of a magnetic tunnel junction (MTJ) produce a new system that differs dramatically from the properties of isolated molecules and ferromagnets. However, it is unknown how far deep in the ferromagnetic electrode the impact of the paramagnetic molecule and ferromagnet interactions can travel for various levels of molecular spin states. Our prior experimental studies showed two types of paramagnetic SMMs, the hexanuclear Mn6 and octanuclear Fe-Ni molecular complexes, covalently bonded to ferroma…
Radial distribution and its spherical harmonics expansion in liquid CO2 at 250 K and 50 bar based on pressure-constant Monte Carlo simulation using Kihara Potential Model
Well-protected magnetization, tunable quantum states and long coherence time are desired for the use of magnetic molecules in spintronics and quantum information technologies. In this work, endohedral fullerene molecules M@C28 with different transition metal cores were explored through systematic first-principles calculations and spin dynamics analyses. Many of them have stable magnetization, giant magnetic anisotropy energy and bias-tunable structure. In particular, some of them may have coherence time up to several milliseconds for their quantum spin states at high temperature (~10K) after f…
We report chirality-induced current-in-plane magnetoresistance (CIP-MR) in chiral molecule/ferromagnetic metal bilayer at room temperature. The previously reported chiralityinduced current-perpendicular-to-plane magnetoresistance (CPP-MR) originates from the chiral induced spin-selectivity (CISS) effect that needs charge-current passing through the molecule. In contrast, the observed CIP-MR in the present study requires no bias charge current through the molecule. The temperature dependence of CIP-MR suggests thermally induced spin-polarization in the chiral molecules is the key for the observ…
Magnetization versus field measurements were performed on single crystals of [(Pc)2TbIII0.02YIII0.98]^TBA+ and [(Pc)2DyIII0.02YIII0.98]^TBA+ (Pc: phthalocyaninato, TBA: tetrabutylammonium) at 0.04 K. The [(Pc)2TbIII] complex, the first lanthanide single-molecule magnet, exhibited clear staircase-like structures, which are assigned to resonant quantum tunneling between entangled states of the electron and nuclear spin systems.
Search for Axions and Dark Photons Using Single Molecule Magnets
Universidade Federal do Rio Grande do Norte（北里奥格兰德联邦大学）；International Institute of Physics, Universidade Federal do Rio Grande do Norte（北里奥格兰德联邦大学国际物理研究所）；Max Planck Institut fur Kernphysik（马克斯·普朗克核物理研究所）；Millennium Institute for Subatomic Physics at the High-Energy Frontier (SAPHIR) of ANID（智利国家研究与发展署高能前沿亚原子物理千年研究所(SAPHIR)）；Universidad de La Serena（拉塞雷纳大学）；Universidade do Estado do Rio Grande do Norte（北里奥格兰德州立大学）
