Strength Of Dipolar Interaction Research Articles

Quantum information processing with nuclear spins mediated by a weak-mechanically controlled electron spin

We propose a scheme to achieve nuclear–nuclear indirect interactions mediated by a mechanically driven nitrogen-vacancy (NV) center in a diamond. Here we demonstrate two-qubit entangling gates and quantum-state transfer between two carbon nuclei. When the dipole–dipole interaction strength is much larger than the driving field strength, the scheme is robust against decoherence caused by coupling between the NV center (nuclear spins) and the environment. Conveniently, precise control of dipole coupling is not required so this scheme is insensitive to fluctuating positions of the nuclear spins and the NV center. Our scheme provides a general blueprint for multi-nuclear-spin gates and for multi-party communication.

Geometric Frustration on the Trillium Lattice in a Magnetic Metal-Organic Framework.

In the dense metal-organic framework Na[Mn(HCOO)_{3}], Mn^{2+} ions (S=5/2) occupy the nodes of a "trillium" net. We show that the system is strongly magnetically frustrated: the Néel transition is suppressed well below the characteristic magnetic interaction strength; short-range magnetic order persists far above the Néel temperature; and the magnetic susceptibility exhibits a pseudo-plateau at 1/3-saturation magnetization. A simple model of nearest-neighbor Heisenberg antiferromagnetic and dipolar interactions accounts quantitatively for all observations, including an unusual 2-k magnetic ground state. We show that the relative strength of dipolar interactions is crucial to selecting this particular ground state. Geometric frustration within the classical spin liquid regime gives rise to a large magnetocaloric response at low applied fields that is degraded in powder samples as a consequence of the anisotropy of dipolar interactions.

Self-bound dipolar droplets and supersolids in molecular Bose-Einstein condensates

We numerically study the many-body physics of molecular Bose-Einstein condensates with strong dipole-dipole interactions. We observe the formation of self-bound droplets, and explore phase diagrams that feature a variety of exotic supersolid states. In all of these cases, the large and tunable molecular dipole moments enable the study of unexplored regimes and phenomena, including liquid-like density saturation and universal stability scaling laws for droplets, as well as pattern formation and the limits of droplet supersolidity. We discuss a realistic experimental approach to realize both the required collisional stability of the molecular gases and the independent tunability of their contact and dipolar interaction strengths. Our work provides both a blueprint and a benchmark for near-future experiments with bulk molecular Bose-Einstein condensates.

Magnetic relaxation in two dimensional assembly of dipolar interacting nanoparticles

We perform extensive kinetic Monte Carlo simulations to investigate the magnetic relaxation characteristics in a two-dimensional (Lx×Ly) assembly of magnetic nanoparticles (MNPs) as a function of dipolar interaction strength hd, aspect ratio Ar=Ly/Lx, and temperature T. The anisotropy axes are taken as randomly oriented in three-dimensional space. In the presence of small dipolar interaction (hd≤0.3) and substantial temperature, the magnetic relaxation follows the Néel Brown model as expected. Interestingly, the dipolar interaction of enough strength is found to induce antiferromagnetic coupling in the square arrangement of MNPs (Ar=1.0), resulting in the fastening of magnetic relaxation with hd. There is also a rapid increase in relaxation even with Ar<100 above a particular dipolar interaction strength hd⋆, which gets enhanced with Ar. Remarkably, magnetization relaxes slowly with hd for the highly anisotropic system, i.e. Ar>100. It is because the dipolar interaction induces ferromagnetic interaction in such a case. The temperature also affects relaxation drastically. For weak dipolar interaction, magnetization relaxes rapidly with T because of enhancement in thermal fluctuations. The effective Néel relaxation time τN also depends strongly on these parameters. In the presence of strong dipolar interaction (hd>0.3) and Ar=1.0, τN decreases with hd for a given temperature. On the other hand, there is an increase in τN with hd for huge Ar(>100). The comparison of relaxation behaviour and τN with aligned anisotropy cases also reveals a strong dependence of these characteristics on the anisotropy axes orientation. These results are beneficial in data storage and other spintronics based applications.

Anisotropic effect of dipolar interaction in ordered ensembles of nanoparticles

We implement extensive computer simulations to investigate the hysteresis characteristics in the ordered arrays (lx × ly) of magnetic nanoparticles as a function of aspect ratio Ar = ly/lx, dipolar interaction strength hd, and external magnetic field directions. We have considered the aligned anisotropy case, α is the orientational angle. It provides an elegant en route to unearth the explicit role of anisotropy and dipolar interaction on the hysteresis response in such a versatile system. The superparamagnetic character is dominant with weak dipolar interaction (hd ≤ 0.2), resulting in the minimal hysteresis loop area. Remarkably, the double-loop hysteresis emerges even with moderate interaction strength (hd ≈ 0.4), reminiscent of antiferromagnetic coupling. These features are strongly dependent on α and Ar. Interestingly, the hysteresis loop area increases with hd, provided Ar is enormous, and the external magnetic field is along the y-direction. The coercive field μoHc, remanent magnetization Mr, and the heat dissipation EH also depend strongly on these parameters. Irrespective of the external field direction and weak dipolar interaction (hd ≤ 0.4), there is an increase in μoHc with hd for a fixed α and Ar ≤ 4.0. The dipolar interaction also elevates Mr as long as Ar is huge and the field is along the y-direction. EH is minimal for negligible and weak dipolar interaction, irrespective of Ar, α, and the field directions. Notably, the magnetic interaction enhances EH if Ar is enormous and the magnetic field is along the long axis of the system. These results are beneficial in various applications of interest such as digital data storage and spintronics. (a) Schematic of the two-dimensional array of nanoparticles. The variation of heat dissipation EH as a function of dipolar interaction strength and anisotropy axis orientation is shown in (b)-(d). The magnetic field is applied along the x-direction in (b). In contrast, the magnetic field is applied along y-direction in (c) and (d).

The studies on phonons and magnons in [CoFeB/Au]N multilayers of different number of repetitions

We investigated the interaction between spin waves and surface acoustic waves in the [CoFeB/Au]N multilayer deposited on the silicon substrate by Brillion light scattering spectroscopy. We showed that this kind of coupling manifested as an anticrossing in magnetoelastic dispersion relation, can be modified by changing the number of repetitions within the multilayer. The observed modification is attributed mostly to the change in the strength of dipolar interactions which alter the dispersion branch of spin wave fundamental mode and shifts the anticrossing towards larger wave vectors where the magnetoelastic coupling is stronger. The studied range of the wave vector was varied between 0.6·105 cm−1 and 2.2·105 cm−1 while the frequency range of investigations was between 3 and 20 GHz.

Silica incorporation into sodium aluminum phosphate glasses: Structural characterization by Raman spectroscopy and multinuclear solid-state NMR

Optical fiber glasses in the system (59-xP2O5)-xSiO2–13Al2O3-28Na2O show non-linear trends in the glass-transition temperatures, thermal expansion coefficients, and weathering stabilities. The structural origins have been studied using solid-state NMR and Raman spectroscopies on a series of bulk glasses with 0 ≤ x ≤ 13. Two types of P2 units – those dominantly interacting with Na+and those interacting more strongly with Al can be differentiated by 31P{23Na} and 31P{27Al} double resonance experiments. Silicon is four-coordinated, fully polymerized, and engaged in Si-O-P linkages. Trends in the 29Si chemical shifts and the 31P-31P dipolar interaction strengths are related to the Si-O-P, Si-O-Al, and P-O-P connectivity distributions, providing a rationale for changes in macroscopic properties.

Controlling local relaxation in small clusters of magnetic nanoparticles

We investigate the local (particle level) and averaged magnetic relaxation characteristics in linear chain-like agglomerates of k magnetic nanoparticles (MNPs) or k-mers using computer simulations. The local relaxation behaviour is dictated by the corresponding dipolar field acting on the nanoparticle, irrespective of k-mer size. There is a wide variation in local relaxation characteristics as a function of nanoparticle position in a small nanocluster. On the other hand, there is more uniformity in the local relaxation response with a larger k-mer, except for MNPs at the boundary. Interestingly, there is a smooth decay of magnetization with small hd, independent of cluster size. In contrast, the magnetization ceases to relax in the presence of substantial dipolar interaction strength. Remarkably, the local Néel relaxation time τNi is directly proportional to the corresponding dipolar field. Likewise, the averaged Néel relaxation time τN also depends strongly on the k-mer size and hd.

Simulation of magneto-mechanical response of ferrogel samples with various polymer structure

ABSTRACT Following the coarse-grained molecular dynamics approach, we propose a model of a small ferrogel sample (containing up to 1000 magnetic nanoparticles), in which the polymer matrix is presented in the form of a quasi-regular mesh of spring-beads chains and the filler particles are located at the mesh nodes. The state of the sample in the absence of an external field and in the process of quasi-static magnetization is considered for two types of mesh topology (simple cubic and diamond-like), different values of the filler concentration, the strength of dipole interaction, and the energy of magnetic anisotropy. Simulation shows that the use of a softer matrix with a diamond-like structure increases the magneto-mechanical response of the ferrogel. The presence of magnetic anisotropy leads to effective hardening of the ferrogel and, thus, prevents particle clustering and sample magnetization. It was also found that the anisotropy energy determines the type of field-induced changes in the sample volume – this aspect of material behavior is important for the use of ferrogels in controlled delivery and/or release of drugs.

Quantum steering over an entangled network that is generated via Dipolar interaction

The possibility of steering a member by another one of a quantum network that is generated via Dipolar interaction is discussed. It is shown that, the steerability of direct connected members is much larger than that depicted for the indirect connected members. Although the steerability degree decreases as the interaction time increases, the regions in which the steering is possible increases. The violation and satisfaction of the steerability are displayed periodically as the interaction time increases. It is shown that, the steerability and its degree increase as the quantum correlation between the steerer and the steered member increases. Consequently, the strength of Dipolar interaction could be considered as a control parameter to maximize/minimize the steerability.

Hysteresis in two dimensional arrays of magnetic nanoparticles

We perform computer simulations to probe the magnetic hysteresis in a two-dimensional (Lx×Ly) assembly of magnetic nanoparticles as a function of dipolar interaction strength hd, temperature T, aspect ratio Ar=Ly/Lx, and the applied alternating magnetic field’s direction. In the absence of magnetic interaction (hd≈0) and thermal fluctuations (T=0 K), the hysteresis follows the Stoner and Wohlfarth model, as expected. For weak dipolar interaction and substantial temperature, the hysteresis has the dominance of superparamagnetic behaviour, irrespective of the applied magnetic field’s direction and Ar. Interestingly, the hysteresis curve has all the characteristics of antiferromagnetic interaction dominance for Ar≤6 and considerable dipolar interaction strength (hd>0.2), independent of applied magnetic direction. When the magnetic field is applied along the system’s shorter axis (x-direction), a non-hysteresis straight line is observed with large hd. In the case of the magnetic field applied along the long axis of the sample (y-direction), ferromagnetic interaction dominates the hysteresis for large hd and Ar>6. Irrespective of hd and applied magnetic field’s direction, the coercive field μoHc and remanence Mr are minimal for Ar≤6 and significant temperature. They are found to increase with hd when Ar is enormous. There is a strong dependence of μoHc and Mr on temperature for weakly interacting MNPs. While for large hd, they depend weakly on temperature. Remarkably, the variation of hysteresis loop area EH as a function of these parameters is the same as that of the coercive field variation. We believe that the concepts presented in this work are relevant in various technological applications such as spintronics and magnetic hyperthermia, in which such self-assembled nanoparticle arrays are ubiquitous.

Tailoring Local Hysteresis in Small Clusters of Dipolar Interacting Magnetic Nanoparticles

Using first-principle calculations and kinetic Monte Carlo simulation, we study the local and averaged hysteresis in tiny clusters of [Formula: see text] magnetic nanoparticles (MNPs) or [Formula: see text]-mers. We also analyze the variation of local dipolar field acting on the constituent nanoparticles as a function of the external magnetic field. The dipolar interaction is found to promote chain-like arrangement in such a cluster. Irrespective of cluster size, the local hysteresis response depends strongly on the corresponding dipolar field acting on a nanoparticle. In a small [Formula: see text]-mer, there is a wide variation in local hysteresis as a function of nanoparticle position. On the other hand, the local hysteresis is more uniform for larger [Formula: see text]-mer, except for MNPs at the boundary. In the case of superparamagnetic nanoparticle and weak dipolar interaction, the local hysteresis loop area [Formula: see text] is minimal and depends weakly on the [Formula: see text]-mer size. While for ferromagnetic counterpart, [Formula: see text] is considerably large even for weakly interacting MNPs. The value of [Formula: see text] is found to be directly proportional to the dipolar field acting on the nanoparticle. The dipolar interaction and [Formula: see text]-mer size also enhance the coercivity and remanence. There is always an increase in [Formula: see text] with cluster size and dipolar interaction strength. Similarly, the averaged hysteresis loop area [Formula: see text] also depends strongly on the [Formula: see text]-mer size, particle size and dipolar interaction strength. [Formula: see text] and [Formula: see text] always increase with [Formula: see text]-mer size and dipolar interaction strength. Interestingly, the value of [Formula: see text] saturates for [Formula: see text] and considerable dipolar interaction irrespective of particle size. We believe that this work would help understand the intricate role of dipolar interaction on hysteresis and the organizational structure of MNPs and their usage in drug delivery and hyperthermia applications.

Study of magnetization relaxation in molecular spin clusters using an innovative kinetic Monte Carlo method

Modeling blocking temperature in molecular magnets has been a long standing problem in the field of molecular magnetism. We investigate this problem using a kinetic Monte Carlo (kMC) approach on an assembly of 100,000 short molecular magnetic chains (SMMCs), each of six identical spins with nearest neighbour anisotropic ferromagnetic exchange interactions. Each spin is also anisotropic with an uniaxial anisotropy. The site spin on these SMMCs take values $1$, $3/2$ or $2$. Using eigenstates of these SMMCs as the states of Markov chain, we carry out a kMC simulation starting with an initial state in which all SMMCs are completely spin polarized and assembled on a one-dimensional lattice so as to experience ferromagnetic spin-dipolar interaction with each other. From these simulations we obtain the relaxation time $\tau_r$ as a function of temperature and the associated blocking temperature. We study this for different exchange anisotropy, on-site anisotropy and strength of dipolar interactions. The magnetization relaxation times show non-Arrhenius behaviour for weak on-site interactions. The energy barrier to magnetization relaxation increases with increase in on-site anisotropy, exchange anisotropy and strength of spin dipolar interactions; more strongly on the last parameter. In all cases the barrier saturates at large on-site anisotropy. The barrier also increases with site spin. The large barrier observed in rare-earth single ion magnets can be attributed to large dipolar interactions due to short intermolecular distances, owing to their small size and large spin of the rare earth ion in the molecule.

Ion‐Dipole Chemistry Drives Rapid Evolution of Li Ions Solvation Sheath in Low‐Temperature Li Batteries

AbstractSluggish evolution of lithium ions’ solvation sheath induces large charge‐transfer barriers and high ion diffusion barriers through the passivation layer, resulting in undesirable lithium dendrite formation and capacity loss of lithium batteries, especially at low temperatures. Here, an ion‐dipole strategy by regulating the fluorination degree of solvating agents is proposed to accelerate the evolution of the Li+ solvation sheath. Ethylene carbonate (EC)‐based fluorinated derivatives, fluoroethylene carbonate (FEC) and di‐fluoro ethylene carbonate (DFEC) are used as the solvating agents for a high dielectric constant. As the increase of the fluorination degree from EC to FEC and DFEC, the Li+‐dipole interaction strength gradually decreases from 1.90 to 1.66 and 1.44 eV, respectively. Consequently, the DFEC‐based electrolyte displays six times faster ion desolvation rate than that of a non‐fluorinated EC‐based electrolyte at −20 °C. Furthermore, LiNi0.8Co0.1Mn0.1O2||lithium cells in a DFEC‐based electrolyte retain 91% original capacity after 300 cycles at 25 °C, and 51% room‐temperature capacity at −30 °C. By bridging the gap between the ion‐dipole interactions and the evolution of Li+ solvation sheath, this work provides a new technique toward rational design of electrolyte engineering for low‐temperature lithium batteries.

Ground states of two-dimensional tilted dipolar bosons with density-induced hopping

Motivated by recent experiments with ultracold magnetic atoms trapped in optical lattices where the orientation of atomic dipoles can be fully controlled by external fields, we study, by means of quantum Monte Carlo, the ground-state properties of dipolar bosons trapped in a two-dimensional lattice with density-induced hopping and where the dipoles are tilted along the $xz$ plane. We present ground-state phase diagrams of the above system at different tilt angles. We find that as the dipolar interaction increases, the superfluid phase at half-filling factor is destroyed in favor of either a checkerboard or stripe solid phase for tilt angle $\ensuremath{\theta}\ensuremath{\lesssim}{30}^{\ensuremath{\circ}}$ or $\ensuremath{\theta}\ensuremath{\gtrsim}{30}^{\ensuremath{\circ}}$, respectively. More interesting physics happens at tilt angles $\ensuremath{\theta}\ensuremath{\gtrsim}{58}^{\ensuremath{\circ}}$, where we find that as the dipolar interaction strength increases, solid phases first appear at filling factor lower than 0.5. Moreover, unlike what is observed at lower tilt angles, we find that at half filling, a stripe supersolid intervenes between the superfluid and stripe solid phase.

Spin-ice physics in cadmium cyanide

Spin-ices are frustrated magnets that support a particularly rich variety of emergent physics. Typically, it is the interplay of magnetic dipole interactions, spin anisotropy, and geometric frustration on the pyrochlore lattice that drives spin-ice formation. The relevant physics occurs at temperatures commensurate with the magnetic interaction strength, which for most systems is 1–5 K. Here, we show that non-magnetic cadmium cyanide, Cd(CN)2, exhibits analogous behaviour to magnetic spin-ices, but does so on a temperature scale that is nearly two orders of magnitude greater. The electric dipole moments of cyanide ions in Cd(CN)2 assume the role of magnetic pseudospins, with the difference in energy scale reflecting the increased strength of electric vs magnetic dipolar interactions. As a result, spin-ice physics influences the structural behaviour of Cd(CN)2 even at room temperature.

Bénard–von Kármán vortex street in a dipolar Bose–Einstein condensate

The Bénard–von Kármán vortex street in dipolar Bose–Einstein Condensate trapped by a harmonic potential is investigated numerically. The results show that when the velocity of the obstacle potential increases to a certain value and for a suitable potential width, the vortex pairs released from the moving obstacle potential alternately will form a periodic anti-symmetric double-row in dipolar BEC, and forming a Bénard–von Kármán vortex street. The influence of the dipole interaction strength, the width and the velocity of the obstacle potential on the vortex structure produced in the wake is also studied, and the structure of the phase diagram is obtained. The drag force on the obstacles potential is calculated, and the mechanical mechanism of vortex pair is analyzed.

Spin waves in unsaturated single- and double-layered ferromagnetic nanorings

A theoretical analysis is described for the spin waves in single- and double-layered nanorings using a microscopic, or Hamiltonian-based, formalism. The calculations, which yield the frequencies and spatially-dependent intensities of the quantized spin waves, are applied to the vortex and onion (bi-domain) states in a single nanoring, as well as to the field-induced switching. In the case of asymmetric double-layered nanorings (with a nonmagnetic spacer) there are coupled spin waves controlled by varying the spacer thickness to change the strength of the inter-ring dipolar interactions. The different possible magnetic states, depending on the applied magnetic field, may involve vortex states (with the same or opposite chirality) in both layers, a vortex state in one layer and onion state in the other, or onion states in both layers. Numerical applications are made to permalloy nanorings with realistic dimensions and magnetic parameter values.

ARC 3.0: An expanded Python toolbox for atomic physics calculations

ARC 3.0 is a modular, object-oriented Python library combining data and algorithms to enable the calculation of a range of properties of alkali and divalent atoms. Building on the initial version of the ARC library (Šibalić et al., 2017), which focused on Rydberg states of alkali atoms, this major upgrade introduces support for divalent atoms. It also adds new methods for working with atom–surface interactions, for modelling ultracold atoms in optical lattices and for calculating valence electron wave functions and dynamic polarisabilities. Such calculations have applications in a variety of fields, e.g., in the quantum simulation of many-body physics, in atom-based sensing of DC and AC fields (including in microwave and THz metrology) and in the development of quantum gate protocols. ARC 3.0 comes with an extensive documentation including numerous examples. Its modular structure facilitates its application to a wide range of problems in atom-based quantum technologies. Program summaryProgram Title: ARC 3.0CPC Library link to program files:https://doi.org/10.17632/c4z4n2cdf7.1Licencing provisions: BSD-3-ClauseProgramming language: PythonExternal Routines: NumPy [1], SciPy [1], Matplotlib [2], SymPy [3], LmFit [4]Nature of problem: The calculation of atomic properties of alkali and divalent atoms including energies, Stark shifts and dipole–dipole interaction strengths using matrix elements evaluated through a variety of means.Solution method: Dipole matrix elements are calculated using an analytical semi-classical approximation or wave functions obtained by numerical integration of the radial Schrödinger equation for a one-electron model potential. Interaction energies and shifts due to external fields are calculated using second order degenerate perturbation theory or exact diagonalisation of the interaction Hamiltonian, yielding results valid even at large external fields or small interatomic separation.Additional comments including restrictions and unusual features: External electric and magnetic field must be parallel to the quantisation axis. The accuracy of short range (≲1μm) atom - atom interaction potentials is limited by the truncation of the basis. Only weak magnetic fields are supported as only linear Zeeman shifts are taken into account. Calculations for divalent atoms use a single-electron approximation and calculation of their wave functions is not supported.

Thermal and dipolar interaction effect on the relaxation in a linear chain of magnetic nanoparticles

We perform computer simulations to study the relaxation in a one-dimensional chain of dipolar interacting magnetic nanoparticles (MNPs). Using the two-level approximation of the energy barrier, we perform kinetic Monte Carlo simulations to probe the relaxation mechanism as a function of dipolar interaction strength and temperature. The anisotropy axes of the MNPs are assumed to have random orientations. At high temperatures, the magnetization decay curve is exponential for weak dipolar interactions. It is found that dipolar interactions slow down the magnetic relaxation and increase the effective Néel relaxation time τN, which is affected by thermal fluctuations. In the weak dipolar limit, there is a perfect agreement between simulated and analytically evaluated values of τN for a wide range of temperatures. Microscopic analyses such as magnetic moments correlations and dynamic domain formation also suggest an increase in ferromagnetic coupling with an increase in dipolar interaction strength or decrease in thermal fluctuations. We believe that the concepts presented in this work are relevant in the context of applications such as data storage, digital data processing, and magnetic hyperthermia, in which the linear chain of MNPs are pervasive.