Effect Of Single-ion Anisotropy Research Articles

Coordination complexes of isoquinoline with cobalt and nickel halides

Reaction of isoquinoline (iQuin) with cobalt(II) and nickel(II) chloride and bromide produced a family of neutral coordination complexes: (iQuin)2CoX2 [X = Cl (1), Br (2)], (iQuin)4CoX2 (X = Cl (3), X = Br (4)], (iQuin)4NiX2 [X = Cl, (5), X = Br, (6)], and (iQuin)2NiBr2(CH3CN)2 (7). The crystal structures of 1–5 and 7 are reported. The majority of the compounds crystallize with some of the iQuin ligands undergoing a ∼2-fold rotational disorder, likely caused by the nearly equivalent space occupied by the two positions. The disorder is temperature independent and ∼50:50 in all cases but one. Magnetic measurements for all seven compounds indicate that their behavior is dominated by single-ion anisotropy effects with indications of antiferromagnetic exchange also present in 1 and 2.

Effective-field theory with the probability distribution technique for a spin-3/2 core and spin-2 shell Ising nanowire: Thermodynamic properties and hysteresis behaviors

The probability distribution technique, exploited within the framework of effective field theory and the Ising model, was used to study the magnetic and thermal properties of a nanowire assimilated to a hexagonal shaped system of a core–shell structure and with mixed spins (3/2,2), respectively. The coupling between core and shell is ferrimagnetic. Under certain physical parameter values, the nanowire exhibits the compensation behavior. The hysteresis behavior was investigated in the presence of an external magnetic field by magnetizing and demagnetizing the nanowire, as well as the effects of single ion anisotropy, ferrimagnetic exchange interactions and temperature on hysteresis loops. The dependence of the shapes of loops on the physical parameters of the system has been elucidated. At low temperatures, the nanowire exhibits triple, quadruple, quintuple, sextuple, septuple and nonuple hysteresis loop behaviors, which have important technological applications. Furthermore, the thermodynamic properties of the nanowire was also studied by evaluating the susceptibility, the internal energy and specific heat for a variety of system physical parameters.

Негейзенберговский ферримагентик с одноионной анизотропией

We have investigated the effect of single-ion anisotropy of the "easy plane" type on the phase states of a ferrimagnet with S = 1 and σ=1/2 sublattices and non-Heisenberg (bilinear and biquadratic in spins) exchange interaction for the sublattice with S = 1. It is shown that taking into account both the non-Heisenberg exchange interaction and the single-ion anisotropy of the sublattice with S = 1 leads to the realization of a phase with vector order parameters (ferrimagnetic phase) and a phase characterized by both vector and tensor order parameters (quadrupole-ferrimagnetic). It is shown that taking into account single-ion anisotropy changes the type of phase transition in comparison with an isotropic non-Heisenberg ferrimagnet. A phase diagram is constructed, and the condition for the compensation of the sublattice spins is determined.

Non-Heisenberg ferrimagnet with single-ion anisotropy

We have investigated the effect of single-ion anisotropy of the "easy plane" type on the phase states of a ferrimagnet with S=1 and sigma=1/2 sublattices and non-Heisenberg (bilinear and biquadratic in spins) exchange interaction for the sublattice with S=1. It is shown that taking into account both the non-Heisenberg exchange interaction and the single-ion anisotropy of the sublattice with S=1 leads to the realization of a phase with vector order parameters (ferrimagnetic phase) and a phase characterized by both vector and tensor order parameters (quadrupole-ferrimagnetic). It is shown that taking into account single-ion anisotropy changes the type of phase transition in comparison with an isotropic non-Heisenberg ferrimagnet. A phase diagram is constructed, and the condition for the compensation of the sublattice spins is determined. Keywords: ferrimagnet, biquadratic exchange interaction, single-ion anisotropy "easy plane", quadrupole-ferrimagnetic phase, phase transition.

Single-ion anisotropy effects on the critical behaviors of quantum entanglement and correlation in the spin-1 Heisenberg chain

Quantum entanglement and correlations in the spin-1 Heisenberg chain with single-ion anisotropy are investigated using the quantum renormalization group method. Negativity and quantum discord (QD) are calculated with various anisotropy parameters △ and single-ion anisotropy parameters D. We focus on the relations between two abovementioned physical quantities and on transitions between the Néel, Haldane, and large-D phases. It is found that both negativity and QD exhibit step-like patterns in different phases as the size of the system increases. Interestingly, the single-ion anisotropy parameter D, which can be modulated using nuclear electric resonance (2020 Nature 579 205), plays an important role in tuning the quantum phase transition (QPT) of the system. Both the first partial derivative of the negativity and QD with respect to D or △ exhibit nonanalytic behavior at the phase transition points, which corresponds directly to the divergence of the correlation length. The quantum correlation critical exponents derived from negativity and QD are equal, and are the reciprocal of the correlation length exponent at each critical point. This work extends the application of quantum entanglement and correlations as tools for depicting QPTs in spin-1 systems.

Magnetism in a graphene-like Ising (spin-1/2) nanoparticle decorated with spin-1 atom

ABSTRACT The phase diagram and the thermal variations of magnetizations in a graphene-like Ising nanoparticle decorated with spin-1 atom are examined by the effective-field theory with correlations. The effects of single-ion anisotropy of spin-1 atom to the magnetic properties are discussed. The following facts are clarified, when the appropriate conditions are satisfied: The transition temperature of the nanoparticle may become larger than that of bulk honeycomb lattice. The decorated nanoparticle exhibits many characteristic phenomena observed in bulk ferrimagnetic materials.

Effect of Single-Ion Anisotropy on Magnetocaloric Properties of Frustrated Spin-s Ising Nanoclusters

Effects of a single-ion anisotropy on magnetocaloric properties of selected spin-s≥1 antiferromagnetic Ising clusters with frustration-inducing triangular geometry are studied by exact enumeration. It is found that inclusion of the single-ion anisotropy parameter D can result in a much more complex ground-state behavior, which is also reflected in a magnetocaloric effect (MCE) at finite temperatures. For negative D (easy-plane anisotropy) with increasing s, the ground-state magnetization as a function of the external field gradually shows increasing number of plateaus of various heights. Except for the cases of integer s with D<D0≤0, the first magnetization plateau is of non-zero height. This property facilitates an enhanced MCE in the adiabatic demagnetization process in the form of an abrupt decrease in temperature as the magnetic field vanishes to zero. The cooling rate can be considerably enhanced in the systems with larger s and D>0 (easy-axis anisotropy), albeit its dependence on these parameters is strongly dependent on the cluster geometry. From the studied systems more favorable conditions for observing a giant MCE were found in the 2CS cluster, consisting of two corner-sharing tetrahedra, the experimental realization of which could be technologically used for efficient refrigeration to ultra-low temperatures.

Single-ion anisotropy effects on the demagnetization process of the alternating weak-rung interacting mixed spin-(1/2, 1) Ising-Heisenberg double saw-tooth ladders

The entropy and cooling property of the mixed spin-(1/2, 1) Ising-Heisenberg double saw-tooth ladder are rigorously examined under an adiabatic demagnetization process using the classical transfer-matrix formalism. The model is characterized once by XXX and once by XX interactions between the interstitial Heisenberg dimers. An Ising-type coupling links spins localized on the legs and rungs. We investigate the ability of cooling/heating of the models nearby some typical critical points. It is evidenced that both models exhibit an enhanced magnetocaloric effect in a proximity of the magnetization steps and jumps. During an adiabatic demagnetization process, a sharp temperature drop is seen close to the first-order zero-temperature phase transitions. We conclude that the single-ion anisotropy considered for the integer spins plays an essential role to determine an efficiency of the magnetocaloric effect of the models under consideration.

Dynamic and Static Properties of a Two-Sublattice Anisotropic Non-Heisenberg Magnet

The effect of single-ion anisotropy on the phase states and dynamic properties of a non-Heisenberg magnet with S = 1 is investigated in the mean field approximation. It is shown that, in contrast to the isotropic model, the inclusion of single-ion anisotropy changes the type of phase transitions between the dipole and nematic phases and leads to the disappearance of the SU(3) point. The phase diagram is constructed.

Hysteresis Cycle and Magnetization Behaviors of a Mixed-Spin (7/2, 3/2) Ferrimagnetic Ising Model: Monte Carlo Investigation

The effects of single-ion anisotropies and an external magnetic field on the magnetization of the mixed-spin (7/2, 3/2) ferrimagnetic Ising system are investigated within Monte Carlo simulation. Under certain values of the physical parameters, multiple hysteresis loop behaviors such as double, triple, and quintuple hysteresis cycles have been observed. Particularly, the superparamagnetic phase has been shown. The ground-state phase diagrams are presented.

Single-ion anisotropy and exchange coupling in cobalt(ii)-radical complexes: insights from magnetic and ab initio studies.

The concurrent effects of single-ion anisotropy and exchange interactions on the electronic structure and magnetization dynamics have been analyzed for a cobalt(ii)-semiquinonate complex. Analogs containing diamagnetic catecholate and tropolonate ligands were employed for comparison of the magnetic behavior and zinc congeners assisted with the spectroscopic characterization and assessment of intermolecular interactions in the cobalt(ii) compounds. Low temperature X-band (ν ≈ 9.4 GHz) and W-Band (ν ≈ 94 GHz) electron paramagnetic resonance spectroscopy and static and dynamic magnetic measurements have been used to elucidate the electronic structure of the high spin cobalt(ii) ion in [Co(Me3tpa)(Br4cat)] (1; Me3tpa = tris[(6-methyl-2-pyridyl)methyl]amine, Br4cat2- = tetrabromocatecholate) and [Co(Me3tpa)(trop)](PF6) (2(PF6); trop- = tropolonate), which show slow relaxation of the magnetization in applied field. The cobalt(ii)-semiquinonate exchange interaction in [Co(Me3tpa)(dbsq)](PF6)·tol (3(PF6)·tol; dbsq- = 3,5-di-tert-butylsemiquinonate, tol = toluene) has been determined using an anisotropic exchange Hamiltonian in conjunction with multistate restricted active space self-consistent field ab initio modeling and wavefunction analysis, with comparison to magnetic and inelastic neutron scattering data. Our results demonstrate dominant ferromagnetic exchange for 3+ that is of similar magnitude to the anisotropy parameters of the cobalt(ii) ion and contains a significant contribution from spin-orbit coupling. The nature of the exchange coupling between octahedral high spin cobalt(ii) and semiquinonate ligands is a longstanding question; answering this question for the specific case of 3+ has confirmed the considerable sensitivity of the exchange to the molecular structure. The methodology employed will be generally applicable for elucidating exchange coupling between orbitally-degenerate metal ions and radical ligands and relevant to the development of bistable molecules and their integration into devices.

Magnetic and thermodynamic properties of a cylindrical ferrimagnetic Ising nanowire with core/shell structure

The Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a cylindrical ferrimagnetic Ising nanowire system with core/shell structure. Phase diagrams are attained with diverse single-ion anisotropies and exchange couplings. It is discovered plentiful phase transitions in the nanowire system, for example, the compensation behaviors, the second-order and first-order phase transitions as well as the tricritical point phenomena. We have discussed the significant effects of single-ion anisotropies, exchange couplings and temperature on the magnetization, the susceptibility, the internal energy and the specific heat for the cylindrical core/shell nanowire system. In addition, we have also found the existence of two types of triple hysteresis loops behaviors for certain physical parameters. It is interesting to achieve satisfying results to compare our results obtained with other theoretical and experimental studies.

The single-ion anisotropy effects in the mixed-spin ternary-alloy

The effect of single-ion anisotropy on the thermal properties of the ternary-alloy in the form of ABpC1−p is investigated on the Bethe lattice (BL) in terms of exact recursion relations. The simulation on the BL consists of placing A atoms (spin-1/2) on the odd shells and randomly placing B (spin-3/2) or C (spin-5/2) atoms with concentrations p and 1−p, respectively, on the even shells. The phase diagrams are calculated in possible planes spanned by the system parameters: temperature, single-ion anisotropy, concentration and ratio of the bilinear interaction parameters for z=3 corresponding to the honeycomb lattice. It is found that the crystal field drives the system to the lowest possible state therefore reducing the temperatures of the critical lines in agreement with the literature.

Some hysteresis loop features of 2D magnetic spin-1 Ising nanoparticle: shape lattice and single-ion anisotropy effects

The effects of longitudinal and transverse crystal-fields on the magnetic hysteresis behaviors of 2D spin-1 Ising nanoparticles are investigated, by using the effective-field theory based on the probability distribution technique with correlations. Nanoparticles with hexagonal or square lattice are studied. A number of characteristic phenomena such as triple and quadruple hysteresis loop behaviors have been observed for certain physical parameters, originating from the competitions among the core/shell exchange interaction, anisotropies, temperature and the longitudinal magnetic field. Finally, the obtained results are compared with some experimental and theoretical results.

Single-Molecule Magnet Behavior Enhanced by Synergic Effect of Single-Ion Anisotropy and Magnetic Interactions.

As the simplest entity carrying intramolecular magnetic interactions, a dinuclear lanthanide complex serves as a model to investigate the effects of magnetic interactions on relaxation of magnetization, and importantly, it proves to be an efficient method to obtain robust single-molecule magnets via improving the communication between lanthanide centers. Here, three Dy2 complexes (1, 2, 3) with a similar structural motif, namely, [Dy2(HL)2(NO3)2(CH3CN)2]·2CH3CN (1), [Dy2(HL)2(NO3)2(DMF)2]·2H2O (2), and Dy2(HL)2(NO3)2(DMF)4 (3), were successfully assembled. One critical difference found in this series of complexes is that the Dy center in complex 3 is coordinated by one more solvent molecule. Surprisingly, complex 3 exhibits the best magnet-like behavior, as evidenced by the high effective barrier and butterfly-type hysteresis, although the crystal field effect around Dy ions is weakened heavily. Ab initio calculations revealed the crucial reason is the significant synergic effect between single-ion anisotropy and magnetic interactions, i.e., not only the axiality of the Dy ion is improved efficiently but also the exchange magnetic interactions increased to the same order of magnitude to the dipolar interaction in 3. This effect mainly benefits from the elaborate modification of the local coordinate environment around the Dy ion, which results in a special arrangement of anisotropy axes different from the other two complexes. It demonstrates that the magnetic interactions could be effectively enhanced by means of deliberate local structural modulation.

Monte Carlo study of magnetization plateaus in a zigzag graphene nanoribbon structure

The Monte Carlo simulation has been applied to discuss the step effect on a zigzag graphene nanoribbon structure in a longitudinal magnetic field. The effects of the singe-ion anisotropies, longitudinal magnetic fields and temperature on the magnetization plateaus have been investigated in detail. Our results show that the number of magnetization plateaus for the system dissatisfy 2S + 1 criterion at low temperatures, originating from not only the competition between the anisotropy and the external magnetic field, but also the contributions of edge effects. It has been found that the single-ion anisotropy plays a significant role in modulating the spin configurations of the zigzag graphene nanoribbon structure. In addition, the effects of single-ion anisotropies and external magnetic fields on the magnetization, the susceptibility, the internal energy and the blocking temperature have been examined.

Classical correlation and quantum entanglement in the mixed-spin Ising-XY model with Dzyaloshinskii–Moriya interaction

In the present work, initially, a mixed-three-spin (1/2,1,1/2) cell of a mixed-[Formula: see text]-spin chain with Ising-XY model is introduced, for which pair spins (1,1/2) have Ising-type interaction and pair spins (1/2,1/2) have both XY-type and Dzyaloshinskii–Moriya (DM) interactions together. An external homogeneous magnetic field [Formula: see text] is considered for the system in thermal equilibrium. Integer-spins have a single-ion anisotropy property with coefficient [Formula: see text]. Then, we investigate the quantum entanglement between half-spins (1/2,1/2), by means of the concurrence. Classical correlation (CC) for this pair of spins is investigated as well as the concurrence and some interesting temperature, the magnetic field and the DM interaction properties are expressed. Moreover, single-ion anisotropy effects on the correlation between half-spins is verified. According to the verifications based on the communication channels category by Rossini, Giovannetti and Fazio [D. Rossini, V. Giovannetti and R. Fazio, Int. J. Quantum Inf. 5, 439 (2007)], we theoretically consider such tripartite spin model as an ideal quantum channel, then calculate its information transmission rate and express some differences in behavior between this suggested model and introduced simple models in the previous works (chains without spin integer and DM interaction) from information transferring protocol point of view.

Field dependence of the magnetic eigenmode frequencies in layered nanowires with ferromagnetic and antiferromagnetic ground states: experimental and theoretical study

The magnetic field dependence of the magnetic eigenmode frequencies in 150 nm wide layered permalloy nanowires (NWs) has been studied by the Brillouin light scattering technique. The NWs have the following layering structure Py(30 nm)/Cu(10 nm)/Py(d)/Cu(10 nm)/Py(30 nm) with fixed thickness of the top and bottom stripe and differ by the thickness d of the middle Py stripe (with d = 15, 30, 60 nm). The magnetic field, applied along the length of the wires, has been swept from positive to negative saturation thus exploring both the ferromagnetic and the antiferromagnetic relative orientation of the magnetization in the middle stripe with respect to the outermost ones. In conjunction with the transition between the two different ground states, the mode frequencies undergo an abrupt variation. Moreover the mode frequencies in the antiferromagnetic state are relatively insensitive to the applied field strength. The experimental results (frequencies versus magnetic field strength) have been successfully interpreted by means of a microscopic (Hamiltonian-based) theory which incorporates both the exchange and dipole–dipole interactions as well as effects of single-ion anisotropy and an external magnetic field applied parallel to the NW axis. This model was extended to account for parallel and antiparallel magnetization orientations in the layered NWs, enabling us to also calculate the probability amplitude of each spin-wave eigenmode at any position in the trilayered NWs.

Magnetic Behavior of Ternary Prussian Blue Analog in Presence Single-Ion Anisotropy

In this work, with help of Monte Carlo simulation method, we have investigated the effects of single-ion anisotropy on magnetic properties of the Prussian blue analog (FepIIMn1-pII)1.5[CrIII(CN)6].nH2O consisting of three different Ising spins SA=3/2, SB=2, and Sc=5/2. We have found that the critical temperature Tc of this system nearly linear changes dependent upon the interaction ratio R for any mixing ratio p value, and the critical interaction Rc decreases for increasing D values. On the other hand, we have shown that the critical and compensation temperature of the model smoothly increase for increasing D values. In addition, we have demonstrated that the magnetic pole inversion can appear, and compensation temperature Tcomp decreases for the increasing external magnetic field, dependent upon some values of the Hamiltonian parameters. As a result, we state that single-ion anisotropy can be used as a control parameter like mixing rate p to arrange the critical and compensation temperature of the Prussian blue analog (FepIIMn1-pII)1.5[CrIII(CN)6].nH2O.

Magnetic-field-induced quantum criticality in a spin-S planar ferromagnet with single-ion anisotropy

The effects of single-ion anisotropy on quantum criticality in a d-dimensional spin-S planar ferromagnet is explored by means of the two-time Green’s function method. We work at the Tyablikov decoupling level for exchange interactions and the Anderson-Callen decoupling level for single-ion anisotropy. In our analysis a longitudinal external magnetic field is used as the non-thermal control parameter and the phase diagram and the quantum critical properties are established for suitable values of the single-ion anisotropy parameter D. We find that the single-ion anisotropy has sensible effects on the structure of the phase diagram close to the quantum critical point. However, for values of the uniaxial crystal-field parameter below a positive threshold, the conventional magnetic-field-induced quantum critical scenario remains unchanged.