Spin Magnetic Interactions Research Articles

Spin-encoded quantum computer near ultimate physical limits

Landauer’s bound is applicable to irreversible quantum operations. In this study, we showcased that the Doppler temperature manifests the existence of Landauer’s bound, which does not block a spin from (irreversibly) flipping with a tiny amount of energy via quantum tunneling. Verified by a spin–spin magnetic interaction experiment, this (energy) amount was determined to be only 1.25 times the theoretical value of Landauer’s bound. Based on Heisenberg’s principle, we defined information from a measuring perspective: one bit of information corresponds to the smallest error when quantifying the product of the measured energy uncertainty (ΔE\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta E$$\\end{document}) and the measured time duration (Δt\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta t$$\\end{document}). We then illustrate an optically manipulated, spin-encoded, near-Landauer-bound, near-Heisenberg-limit quantum computer that encompasses this new definition of information. This study may represent the last piece of the puzzle in understanding both quantum Landauer erasure and Heisenberg’s quantum limit since a single spin is the smallest information carrier.

Spin Catalysis in Photochemical Reactions and Its Applications to Quantum Information Nanotechnology

Chemistry as a science about spin and electric charge of micro particles which provide driving forces of atomic interactions and molecular structure transformations fits pretty well to the modern Quantum Information Science (QIS) requirements. Today’s computers operate only electric current signals in the semiconductor networks but the electron-spin properties are not exploited in a large extend. Spintronics provides spin-polarized currents and manipulates magnetic spin interactions; it uses mostly solid state chemistry of heavy elements. But a rich organic chemistry of solvents and fin films offers a great potential for molecular electronics and quantum computing. Photo-excited organic complexes of the “chromophore–radical” type provide good promise for many technological applications in molecular spintronics and electronics, including QIS technology. The doublet state photo excitation of stable organic radical being delocalized onto the linked anthracene molecule within picoseconds and subsequently evolved into a quartet state for big radicals (a pure high spin state) of the mixed radical-triplet character presents a sensible spin-optical interface for qubit in quantum computing. This high-spin state is coherently addressable with EPR microwaves even at room temperature, with the optical read-out induced by intersystem crossing (ISC) to emissive triplet state. Such integration of radical luminescence and high-spin states EPR provides the organic materials involvement into emerging QIS technologies

Control of magnetic states and spin interactions in bilayer CrCl3 with strain and electric fields: an ab initio study

Using ab initio density functional theory, we demonstrated the possibility of controlling the magnetic ground-state properties of bilayer CrCl_{3} by means of mechanical strains and electric fields. In principle, we investigated the influence of these two fields on parameters describing the spin Hamiltonian of the system. The obtained results show that biaxial strains change the magnetic ground state between ferromagnetic and antiferromagnetic phases. The mechanical strain also affects the direction and amplitude of the magnetic anisotropy energy (MAE). Importantly, the direction and amplitude of the Dzyaloshinskii–Moriya vectors are also highly tunable under external strain and electric fields. The competition between nearest-neighbor exchange interactions, MAE, and Dzyaloshinskii–Moriya interactions can lead to the stabilization of various exotic spin textures and novel magnetic excitations. The high tunability of magnetic properties by external fields makes bilayer CrCl_{3} a promising candidate for application in the emerging field of two-dimensional quantum spintronics and magnonics.

Breaking Landauer's bound in a spin-encoded quantum computer

It is commonly recognized that Landauer's bound holds in (irreversible) quantum measurement. In this study, we overturned this common sense by extracting a single spin from a spin–spin magnetic interaction experiment to demonstrate that Landauer’s bound can be broken quantitatively by a factor of 10^{4} sim 10^{10} via quantum spin tunneling. It is the quantum limit (hbar /2 approx 10^{ - 34} ;{text{J}} cdot {text{s}}), rather than Landauer’s bound, that governs the performance of a spin qubit. An optically-manipulated spin-encoded quantum computer is designed, in which energy bound well below k_{B} T to erase a spin qubit at the expense of a long spin relaxation time is theoretically sensible and experimentally verified. This work may represent the last piece of the puzzle in quantum Landauer erasure in terms of a single spin being the smallest and the closest to the quantum limit.

Anomalous spin dynamics in a two-dimensional magnet induced by anisotropic critical fluctuations

We investigate the temperature dependence of $g$ factor in two-dimensional (2D) ferromagnet ${\mathrm{CrSiTe}}_{3}$ by combining three-dimensional vector-ferromagnetic resonance (FMR) experiments. It is shown from the angular dependence that the dramatic $g$ shift near critical temperature originates from the interplay of enhanced magnetic fluctuations and anisotropic spin interactions in 2D magnetism. The crossover from isotropic to anisotropic $g$ factor for $T\ensuremath{\rightarrow}{T}_{c}$ yields anomalously parallel pumped excitations. In the critical regime, the field suppression of critical fluctuations is associated with the field dependence of $g$ shift. Furthermore, the results of FMR $g$ shift are scaled by susceptibilities and spontaneous magnetization obtained from magnetometry measurements, which show good agreement with the universality class of the 2D Ising model.

Insight view of magneto-electronic, mechanical and thermophysical properties of novel filled skutterudites LiFe4X12 (X = As, Sb) via ab-initio calculations

Using the Density Functional Theory (DFT), we have systematically investigated the structural, mechanical, and thermodynamic stabilities of LiFe4As12 and LiFe4Sb12 skutterudites. Thereafter, estimated their electronic band structure, magnetic as well as transport properties. Spin magnetic interactions were precisely taken into account. Among the different possible magnetic phases, the ferromagnetic phase is thermodynamically most stable accounting least energy. The lattice constant fetched from the structural optimization for LiFe4As12 and LiFe4Sb12 skutterudite shows a decent agreement with the reported lattice parameters of similar other materials. The electronic bands obtained by different approximations like generalized gradient approximation (GGA) and GGA ​+ ​mBJ suggest the metallic character of the materials, with the possibility of high spin polarization. Seebeck coefficient, electronic conductivity, and thermal conductivity are calculated by using the Boltztrap code. Both materials show a substantial value of power factor. The overall strength of the material poses its application for solid-state device fabrications.

Asymmetry in the Ligand Coordination Sphere of the [FeFe] Hydrogenase Active Site Is Reflected in the Magnetic Spin Interactions of the Aza-propanedithiolate Ligand.

[FeFe] hydrogenases are very active enzymes that catalyze the reversible conversion of molecular hydrogen into protons and electrons. Their active site, the H-cluster, contains a unique binuclear iron complex, [2Fe]H, with CN– and CO ligands as well as an aza-propane-dithiolate (ADT) moiety featuring a central amine functionality that mediates proton transfer during catalysis. We present a pulsed 13C-ENDOR investigation of the H-cluster in which the two methylene carbons of ADT are isotope labeled with 13C. We observed that the corresponding two 13C hyperfine interactions are of opposite sign and corroborated this finding using density functional theory calculations. The spin polarization in the ADT ligand is shown to be linked to the asymmetric coordination of the distal iron site with its terminal CN– and CO ligands. We propose that this asymmetry is relevant for the enzyme reactivity and is related to the (optimal) stabilization of the iron-hydride intermediate in the catalytic cycle.

Magnetic ordering contribution on diffusion process forming hollow materials

We have experimentally observed the influence of a magnetic phase transition on the morphological transformation during a thermal oxidation reaction in air due to ionic diffusion process. A Fe ferromagnetic metallic microwire turns into a semiconducting iron oxide microtube when heat treated above the Curie temperature. Electrical transport behavior of Fe microwires measures changes in ionic transport across magnetic transition. Scanning electron microscopy images and x-ray diffraction measurements revealed that the formed microtubes are comprised of a Fe2O3 outer and Fe3O4 inner shells when the sample is heated above the Fe magnetic ordering temperature. This result is closely related to the higher atomic mobility in the paramagnetic state. We discuss the influence of magnetic spin interaction on Fe vacancy formation and the ionic mass transport. Numerical calculations of the vacancy formation energy in both ferromagnetic and paramagnetic states support our experimental observation that enhanced ionic mobility, leaving vacancies behind, is correlated to the vanishing of magnetic spin interactions above TC.

Chemical composition induced quantum phase transition in Cs1−xRbxFeCl3

The isostructural series of $S=1$ quantum magnets Cs$_{1-x}$Rb$_{x}$FeCl$_{3}$ is investigated, using both thermodynamic measurements and inelastic neutron scattering experiments. It is found that increasing Rb content the system evolves from the gapped state at $x=0$, through a quantum phase transition at $x\sim 0.35$, and to the magnetically ordered state at larger $x$. Inelastic neutron experiments for $x=0$, $x=0.3$, and $x=1$ demonstrate that the magnetic anisotropy and spin interactions are continuously tuned by the chemical composition. For the intermediate concentration all magnetic excitations are substantial broadened suggesting that disorder plays a key role in this species. For the two end-compounds, excitations remain sharp.

Normal modes in magnetized two-fluid spin quantum plasmas

We extend the classical two-fluid magnetohydrodynamic (MHD) formalism to include quantum effects such as electron Fermi pressure, Bohm pressure and spin couplings. At scales smaller than the electron skin-depth, the Hall effect and electron inertia must be taken into account, and can overlap with the quantum effects. We write down the full set of two-fluid quantum MHD (QMHD) and analyze the relative importance ofthese effects in the high density environments of neutron star atmospheres and white dwarf interiors, finding that for a broad range of parameters all these effects are operative. Of all spin interactions we analyze only the spin-magnetic coupling, as it is linear in $\hbar$ and consequently it is the strongest spin effect. We re-obtain the classical two-fluid MHD dispersion relations corresponding to the magnetosonic and Alfv\'en modes, modified by quantum effects. In the zero-spin case, for propagation parallel to the magnetic field, we find that the frequency of the fast mode is due to quantum effects modified by electron inertia, while the frequency of the Alfv\'en-slow sector has no quantum corrections. For perpendicular propagation, the fast-mode frequency is the same as for the parallel propagation plus a correction due only to classical two-fluid effects. When spin is considered, a whistler mode appears, which is due to two-fluid spin-magnetic interaction. There are no modifications due to spin for parallel propagation of magnetosonic and Alfv\'en waves, while for perpendicular prop agation a dispersive term due to spin arises in the two-fluid expression for the fast magnetosonic mode.

Study of structural and magnetic properties of co-precipitated α-Fe2O3 nanocrystals

In this study, we have successfully synthesized hematite (α-Fe2O3) nanocrystals by chemical co-precipitation method for different stirring time. Surface morphological studies revealed that shape of the nanoparticles has changed from the rice-like shape to sphere-like shape of nanocrystals on increasing the synthesizing time. In the typical magnetic hysteresis loop, the saturated magnetization value increased from 1.65 to 3.75 emu/g with the reduction of the particle size at room temperature. The synthesized hematite nanocrystals have shown superparamagnetic type blocking temperature TB (∼790 K) below the Neel temperature (∼908 K) due to the size and shape effect of the nanoparticles. These results widen our knowledge about the magnetic spin interaction between antiferromagnetic and canted ferromagnetic arising due to the spin pinning which occurs during field cooling (FC) process through exchange bias effect on 100 min (10.24 nm) sample.

Intersystem crossing mechanism of thermally activated delayed fluorescence copper(I) thiolate complex: The roles of exchange coupling and magnetic spin interactions

The exchange coupling (J) and magnetic dipole (D) interactions of thermally activated delayed fluorescence copper(I) thiolate complex have been investigated by employing computational chemistry methods. The situation of strict orthogonality of the "hole”–“electron" orbitals with the overlap integral 〈ϕ175α|ϕ175β〉 = 0 leads to small J and excessive triplet T1 population, and is unfavorable to the formation of singlet S1 state via the exchange coupling induced reverse intersystem crossing in the triplet state T1. In magnetic dipole interactions, the mutually perpendicular orbitals provides a significant one-center heavy atomic contribution to the SOC, 〈1φ|hySO|3φ〉 = -41.76 and 〈1φ|hzSO|3φ〉 = −63.14 cm−1, which will enhance the probability of intersystem crossing from the T1 to S1, but system needs to overcome a large intersystem crossing barrier height of 11.05 kcal/mol relative to that of the T1 state at the CAM-B3LYP/def2-TZVP(-f) level. Under magnetic field limit, S1−T0, S1−T+1, and S1−T-1 mixing are all inefficient because the large energy gap between T1 and S1, |2J| » gβB prohibits significant mixing in the triplet state T1, but for the S1/T1 crossing point, the S1−T-1 energy gap is comparable to that of the S1−T0 energy gap, allowing for mixing of S1 with T-1 and T0, |Tz〉 = 56%|1, 0〉 + 20%|1, −1〉 + 16%|0, 0〉.

Magnetic and electrical properties of Ti-substituted lanthanum bismuth manganites

We are reporting the influence of non-magnetic Ti ions on magnetic, electrical, magneto-transport, and dielectric responses in polycrystalline ferromagnetic insulating samples $$ {\text{La}}_{ 0. 4} {\text{Bi}}_{ 0. 6} {\text{Mn}}_{{ 1 { - }x}} {\text{Ti}}_{x} {\text{O}}_{ 3} $$ (x = 0.05 and 0.10) synthesized by solid-state route method. Powder X-ray diffraction analysis reveals that the samples crystallize in tetragonal structure indexed to I4/mcm space group. Scanning electron micrographs suggest that the increase in Ti substitution inhibits grain growth process leading to decrease in grain size. The characteristic magnetic dilution with increase in x is evident due to the non-magnetic nature of the Ti ions. Also, in magnetization curve, the observed glassy behavior restricts the long-range magnetic spin interactions in the broader temperatures range. The electrical resistivity measurements exhibited semiconducting nature throughout the measured temperature range (110–300 K) without metal-semiconductor phase transition. The magneto-transport behavior in the paramagnetic region (for T > 150 K) follows $$ \left[ {{\text{MR}}\sim \frac{\Delta \rho }{{\rho \left( {0T} \right)}}} \right] \propto H^{n} $$ relation, giving possible correlation between electrical and magnetic properties. Resistivity data at low temperature region suggest that the conduction is due to the hopping of charge carrier, satisfying SE-VRH mechanism. However, the resistivity data at high-temperature regime suggest the localization of small polarons. The large dielectric responses achieved with multiple relaxations are understood due to extrinsic and intrinsic properties. Complex impedance spectrums have been analyzed using equivalent circuits to determine different contributions responsible for the relaxation process with Ti substitution.

Incommensurate antiferromagnetic order in the manifoldly-frustrated SrTb2O4 with transition temperature up to 4.28 K

The N$\acute{\rm e}$el temperature of the new frustrated family of Sr\emph{RE}$_2$O$_4$ (\emph{RE} = rare earth) compounds is yet limited to $\sim$ 0.9 K, which more or less hampers a complete understanding of the relevant magnetic frustrations and spin interactions. Here we report on a new frustrated member to the family, SrTb$_2$O$_4$ with a record $T_{\rm N}$ = 4.28(2) K, and an experimental study of the magnetic interacting and frustrating mechanisms by polarized and unpolarized neutron scattering. The compound SrTb$_2$O$_4$ displays an incommensurate antiferromagnetic (AFM) order with a transverse wave vector \textbf{Q}$^{\rm 0.5 K}_{\rm AFM}$ = (0.5924(1), 0.0059(1), 0) albeit with partially-ordered moments, 1.92(6) $\mu_{\rm B}$ at 0.5 K, stemming from only one of the two inequivalent Tb sites mainly by virtue of their different octahedral distortions. The localized moments are confined to the \emph{bc} plane, 11.9(66)$^\circ$ away from the \emph{b} axis probably by single-ion anisotropy. We reveal that this AFM order is dominated mainly by dipole-dipole interactions and disclose that the octahedral distortion, nearest-neighbour (NN) ferromagnetic (FM) arrangement, different next NN FM and AFM configurations, and in-plane anisotropic spin correlations are vital to the magnetic structure and associated multiple frustrations. The discovery of the thus far highest AFM transition temperature renders SrTb$_2$O$_4$ a new friendly frustrated platform in the family for exploring the nature of magnetic interactions and frustrations.

Generation of a spin-polarized electron beam by multipole magnetic fields

The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin-magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of this analysis could prove useful in the design of an improved electron microscope.

Spin-electromagnetic hydrodynamics and magnetization induced by spin-magnetic interaction

The hydrodynamic model including the spin degree of freedom and the electromagnetic field is discussed. In this derivation, we apply electromagnetism for a macroscopic medium proposed by Minkowski. For the equation of motion of spin, we assume that the hydrodynamic representation of the Pauli equation is reproduced when the many-body effect is neglected. Then the spin-magnetic interaction in the Pauli equation is converted to a part of the magnetization. The fluid and spin stress tensors induced by the many-body effect are obtained by employing the algebraic positivity of the entropy production in the framework of the linear irreversible thermodynamics, including the mixing effect of the irreversible currents. We further construct the constitutive equation of the polarization and the magnetization. Our polarization equation is more reasonable compared to another result obtained using electromagnetism for a macroscopic medium proposed by de Groot-Mazur.

Microwave-Assisted Synthesis, Microstructure, and Physical Properties of Rare-Earth Chromites

The full rare-earth (RE) chromites series (RE)CrO(3) with an orthorhombic distorted (Pnma) perovskite structure and the isostructural compound YCrO(3) can be synthesized through a simple microwave-assisted technique, yielding high-quality materials. Magnetization measurements evidence that the Néel temperature for antiferromagnetic Cr(3+)-Cr(3+) ordering strongly depends on the RE(3+) ionic radius (IOR), and a rich variety of different magnetic spin interactions exists. Dielectric spectroscopy on sintered pellets indicates electronic inhomogeneity in all samples as manifested by the presence of at least two dielectric relaxation processes associated with grain boundary and grain interior bulk contributions. X-ray diffraction, Raman spectroscopy, and temperature-dependent dielectric permittivity data do not indicate potential noncentrosymmetry in the crystal or concomitant ferroelectricity. Strong correlations between the magnetic and dielectric properties were not encountered, and microwave-synthesized (RE)CrO(3) may not be classified as magnetoelectric or multiferroic materials.

The Pauli equation with complex boundary conditions

We consider one-dimensional Pauli Hamiltonians in a bounded interval with possibly non-self-adjoint Robin-type boundary conditions. We study the influence of the spin–magnetic interaction on the interplay between the type of boundary conditions and the spectrum. Special attention is paid to -symmetric boundary conditions with the physical choice of the time-reversal operator .This article is part of a special issue of Journal of Physics A: Mathematical and Theoretical devoted to ‘Quantum physics with non-Hermitian operators’.

Distance measurements across randomly distributed nitroxide probes from the temperature dependence of the electron spin phase memory time at 240 GHz

At 8.5T, the polarization of an ensemble of electron spins is essentially 100% at 2K, and decreases to 30% at 20K. The strong temperature dependence of the electron spin polarization between 2 and 20K leads to the phenomenon of spin bath quenching: temporal fluctuations of the dipolar magnetic fields associated with the energy-conserving spin “flip-flop” process are quenched as the temperature of the spin bath is lowered to the point of nearly complete spin polarization. This work uses pulsed electron paramagnetic resonance (EPR) at 240GHz to investigate the effects of spin bath quenching on the phase memory times (TM) of randomly-distributed ensembles of nitroxide molecules below 20K at 8.5T. For a given electron spin concentration, a characteristic, dipolar flip-flop rate (W) is extracted by fitting the temperature dependence of TM to a simple model of decoherence driven by the spin flip-flop process. In frozen solutions of 4-Amino-TEMPO, a stable nitroxide radical in a deuterated water–glass, a calibration is used to quantify average spin–spin distances as large as r¯=6.6nm from the dipolar flip-flop rate. For longer distances, nuclear spin fluctuations, which are not frozen out, begin to dominate over the electron spin flip-flop processes, placing an effective ceiling on this method for nitroxide molecules. For a bulk solution with a three-dimensional distribution of nitroxide molecules at concentration n, we find W∝n∝1/r¯3, which is consistent with magnetic dipolar spin interactions. Alternatively, we observe W∝n32 for nitroxides tethered to a quasi two-dimensional surface of large (Ø∼200nm), unilamellar, lipid vesicles, demonstrating that the quantification of spin bath quenching can also be used to discern the geometry of molecular assembly or organization.

Quantum Entanglement Channel based on Excited States in a Spin Chain

We study the possibility of using a spin chain to construct a quantum entanglement channel that can be used for quantum state transmission in a solid state system. We analyze the spin chain's states under various z-directional magnetic field and spin interactions to determine the entanglement between Alice and Bob's spins. We derive the conditions under which this entanglement can be distilled, and find that a spin chain of arbitrary length can be used as a quantum channel for quantum state transmission when the number of spin flips in the chain is large.