Crystal Field Interaction Research Articles

Hydrostatic pressure modulated spin-reorientation transition and magnetocaloric effect in PrGa compound

The effect of hydrostatic pressure on the spin-reorientation transition and magnetocaloric effect in PrGa compound has been experimentally investigated. Because of the significant change of lattice parameter along with the spin reorientation, hydrostatic pressure can largely shift the spin reorientation temperature TSR from 28 K down to 16 K under 1.14 GPa, while magnetic transition at TC∼37 K hardly changes. Although the maximum entropy change ΔSM for a magnetic field change of 0–5T decreases from 9.2 J/kg K to 5.8 J/kg K as a pressure of 1.14 GPa was applied, an asymmetric broadening of ΔSM with magnetic field occurs due to the widening of metamagnetic transition window caused by pressure. As a result, a plateau develops on the ΔSM-T curve, and 10% improvement of effective refrigerant capacity RCeff has been achieved. The origin can be ascribed to the significant impact of the pressure on the lattice and crystal field interaction, which not only strengthens the first-order nature of the spin reorientation transition but also enlarges the distance between TSR and TC and broadens the temperature window of metamagnetic transition involving the specific spin alignment. The tunable TSR and enhanced RCeff by pressure in PrGa demonstrate that the compound can be useful in developing multi-field driven refrigeration technique.

EFT study of critical properties of the mixed spin-2 and spin-3 2 Blume–Capel model on the honeycomb lattice

We use theoretical and numerical calculations in the framework of the effective-field theory to examine the rigorous effects of the crystal field interactions of the mixed spin-2 and spin-[Formula: see text] Blume–Capel model on the honeycomb lattice in the presence of an external magnetic field. The ground state phase diagram has been constructed. Thermal changes of the order parameters and other thermodynamic quantities of interest and their influence on the phase diagrams of the model have been thoroughly investigated. The system shows very interesting critical properties including continuous and discontinuous phase transitions, tricritical points and compensation temperatures which are revealed in specific ranges of the parameters space. Our numerical findings are compared to those obtained by other methods and reliable agreements are recovered.

Excitonic spectra in HgGa2Se4 crystals

Ground and excited states of four excitonic series (A, B, C and D) were discovered in HgGa2Se4 crystals at 10 K. Parameters of excitons and bands were determined. An effective mass of electrons mc is equal to 0.26m0 and masses of holes mv1, mv2 and mv3 are equal to 2.48m0, 2.68m0 and 1.6m0 respectively in Γ point of Brilloin zone. Valence bands splitting by crystal field (Δcf = 70 meV) and spin-orbital interaction (Δso = 250 meV) were estimated in Brillouin zone center. Optical functions (n, ε1 and ε2) for polarizations E⊥c and E||c in electron transitions region (2–6 eV) were calculated by Kramers-Kronig method. The discovered features were discussed on a base of the existing theoretical energetical band structure calculations and excitonic bands symmetries in k = 0 Brillouin zone for chalcopyrite crystals. The resonance Raman scattering was investigated.

Frequency-dependent dynamic magnetic properties of the Ising bilayer system consisting of spin-3/2 and spin-5/2 spins

Dynamic magnetic properties of the Ising bilayer system consisting of the mixed (3/2, 5/2) Ising spins with a crystal–field interaction in an oscillating field on a two-layer square lattice is studied by the use of dynamic mean-field theory based on the Glauber-type stochastic. Dynamic phase transition temperatures are obtained and dynamic phase diagrams are presented in three different planes. The frequency dependence of dynamic hysteresis loops is also investigated in detail. We compare the results with some available theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results.

Magnetic Properties of the Cylindrical Ising Nanowire: A Monte Carlo Simulation Study

A cylindrical ferrimagnetic magnetic nanowire system of core and shell layers has been investigated using Monte Carlo simulation. Critical temperature is obtained for different values of exchange couplings at the core–shell interface, at shell–shell and core–core. The total magnetization has been the determinate for different values of crystal field. Hysteresis loop, coercive field and remanent magnetization of a core and shell layers are obtained using the Monte Carlo simulation. A number of characteristic behaviors are found, such as the occurrence of single and triple hysteresis loops for appropriate values of crystal field, temperatures values and exchange interaction values.

Random crystal field effect on hysteresis loops and compensation behavior of mixed spin-(1,3/2) Ising system

Magnetic hysteresis and compensation behavior of a mixed spin-(1, 3/2) Ising model on a square lattice are investigated in the framework of effective field theory based on a probability distribution technique. The effect of random crystal field, ferromagnetic and ferrimagnetic exchange interaction on hysteresis loops and compensation phenomenon are discussed. A number of characteristic phenomena have been reported such as the observation of triple hysteresis loops at low temperatures and for negative values of random crystal field. Critical and double compensation temperatures have been also found. The obtained results are also compared to some previous works.

The bimodal random crystal field and biquadratic exchange interaction effects for the spin-3/2 Ising model on the Bethe lattice

The phase transition properties of Blume–Emery–Griffiths (BEG) model for the spin-3/2 system are investigated on the Bethe lattice (BL) when the system is under the effect of both random crystal field (D) and biquadratic exchange interaction (K). These randomization effects are either turned on with probability 1−p (q) or turned off with probability p (1−q) for D and K, respectively. The phase diagrams are obtained on the (K/J, kT/J) and (D/J, kT/J) planes for given values of p and q when z=3.0 corresponding to honeycomb lattice. Both attractive (K > 0) and repulsive (K < 0) biquadratic exchange interaction values are considered to examine its effects on the BL. It is found that the model presents either second- or first-order phase transitions and also tricritical points. It is also found that the second-order phase lines follow the phase lines of regular spin-3/2 BEG model as K → ± ∞ for the phase diagrams on the (K/J, kT/J) planes.

Tuning the structural and optical properties in cobalt oxide-doped borosilicate glasses

Borosilicate glass systems with composition xSiO2 - (50-x) B2O3 - 30Na2O - 19.5ZnO - 0.5CoO (x = 0, 5, 10 and 20 mol. %) have been successfully prepared following the traditional melt quenching technique. The incorporation of SiO2 into borate glass network was found to tune its properties at different aspects, as probed by a set of complementary experimental techniques. The density of such boraosilicate glasses was decreased by SiO2 addition, thus, rendering the glassy network less tightly packed. In addition, the BO4 structural units were found to increase with SiO2 content as obtained from comparative FTIR spectra. Interestingly, the optical properties of such borosilicate glasses could be tuned through SiO2 addition. In particular, the optical band gaps attain larger values together with noticeable suppression of the band tails associated with defective structures upon SiO2 addition. Further insights into the crystal field interaction and d-levels splitting were obtained by a detailed deconvolution procedure applied to the characteristic absorption bands of Cobalt. The outcome of such a process revealed noticeable reductions in the ligand field strength and the associated d-levels splitting with SiO2 additives. Furthermore, the octahedral symmetry contribution was increased in borosilicate compared to the pure borate glasses as inferred from the oxidation states of Co ions probed by ESR. The present system combines the advantageous of the pure borate and silicate glasses and, therefore, offers an alternative candidate for optical applications.

Monte Carlo simulation of compensation behavior for a mixed spin-5/2 and spin-7/2 Ising system with crystal field interaction

Monte Carlo simulation has been carried out to study the magnetization of the mixed spin–5/2 and spin–7/2 Ising ferrimagnetic model on a square lattice with periodic boundary conditions. The total magnetization and the magnetizations of the two sublattices under the effects of exchange interactions and the crystal field anisotropy are studied. The ground–state diagrams are constructed. We obtained different types for the thermal dependence of magnetization. Compensation points where the global magnetization of the system vanishes have been detected for appropriate values of the system parameters.

Mixed Spin (1, 5/2) Ising Ferromagnetic Blume-Capel Model Under Time-Dependent Sinusoidal Magnetic Field: an Effective-Field Theory Analysis

Non-equilibrium magnetic properties are studied in a two-dimensional mixed spin (1, 5/2) Blume-Capel Ising system under the influence sinusoidal magnetic fields using the effective-field theory based on a decoupling approximation. A dynamic equation of motion has been solved for a square lattice by utilizing a Glauber-type stochastic process. Dynamic phase diagrams are presented in the reduced magnetic field amplitude and reduced temperature plane (h,T) and reduced crystal-field and reduced temperature plane (Δ,T). We observe that the system exhibits dynamic tricritical behaviors. Phase diagrams contain the paramagnetic (p), ferrimagnetic (i), and coexistence or mixed-phase regions, namely the i,p, and i + p, which strongly depend on the crystal-field interaction parameter and oscillating magnetic field frequency. We have found that the system only exhibits a second-order transition line in the higher-frequency region. We have also compared our result with the mean-field prediction in order to indicate the effects of correlations and found that some of the dynamic first-order phase lines disappeared.

Mixed spin-1 and spin-1/2 Blume-Emery-Griffiths model on the Bethe lattice: Monte Carlo simulation

Using Monte Carlo simulation (MCs), we study thermal and hysteresis behaviors of a mixed spin-1/2 and spin-1 using Blume-Emery Griffiths model. Starting from the spin Hamiltonian which describes the system, the influence of the crystal-field and biquadratic exchange interaction on the critical behaviors has been investigated. Critical exponents were calculated and compared with those of the 3D Ising model.

Influence of chemical composition on the X-ray photoemission, thermopower, specific heat, and magnetic properties of CeNi2(Si1-yGey)2

We report our studies of the intermediate compositions between CeNi2Si2 and CeNi2Ge2, i.e., the alloys CeNi2(Si1-yGey)2 by means of the thermopower, electrical resistivity, specific heat, magnetic susceptibility, and X-ray photoemission measurements. CeNi2Si2 is a fluctuating valence system and CeNi2Ge2 is known to show the heavy fermion behaviour. The change of the temperature dependence of the resistivity towards the typical metallic behaviour occurs below y ~ 0.25. The transition between CeNi2Si2 and CeNi2Ge2 is discussed in the frames of competition between the crystal electric field and Kondo interactions. It is found that valence stabilisation occurs for Ge content y > 0.25. The hybridization energy Δ determined from the XPS Ce 3d spectrum reflects well the behaviour of the parameter Eex obtained from the analysis of the magnetic susceptibility by the interconfiguration fluctuation model. It has been also shown that thermopower data can be successfully described employing the single ion model for 0.6 < y < 1.0 and two-band model including the crystal electric field splitting for y ≤ 0.25.

Anisotropic magnetic switching along hard [1 1 0]-type axes in Er-doped DyFe2/YFe2 thin films

Epitaxial-grown DyFe2/YFe2 multilayer thin films form an ideal model system for the study of magnetic exchange springs. Here the DyFe2 (YFe2) layers are magnetically hard (soft). In the presence of a magnetic field, exchange springs form in the YFe2 layers. Recently, it has been demonstrated that placing small amounts of Er into the centre of the YFe2 springs generates substantial changes in magnetic behavior. In particular, (i) the number of exchange-spring states is increased dramatically, (ii) the resulting domain-wall states cannot simply be described as either Néel or Bloch walls, (iii) the Er and Dy magnetic loops are strikingly different, and (iv) it is possible to engineer Er-induced magnetic exchange-spring collapse. Here, results are presented for Er-doped (110)-oriented DyFe2 (60Å/YFe2(240Å)15 multilayer films, at 100K in fields of up to 12T. In particular, we contrast magnetic loops for fields applied along seemingly equivalent hard-magnetic [110]-type axes. MBE-grown cubic Laves thin films offer the unique feature of allowing to apply the magnetic field along (i) a hard out-of-plane [110]-axis (the growth axis) and (ii) a similar hard in-plane [1¯10]-axis. Differences are found and attributed to the competition between the crystal-field interaction at the Er site and the long-range dipole-dipole interaction. In particular, the out-of-plane [110] Er results show the existence of a new magnetic exchange spring state, which would be very difficult to identify without the aid of element-specific technique of X-ray magnetic circular dichroism (XMCD).

Dynamic Magnetic Hysteresis Behaviors in a Mixed Spin (3/2, 2) Bilayer System with Different Crystal-Field Interactions

Dynamic magnetic hysteresis (DMH) behaviors of the mixed spin-3/2 and spin-2 Ising bilayer system with different crystal-field interactions on a two-layer square lattice is studied by the use of dynamic mean field calculations based on the Glauber-type stochastic. The hysteresis loops are obtained for different reduced temperatures (T), magnetic field amplitudes (h), frequencies (w) and interlayer coupling constants (J3). Influences of the T, h, w and J3 on the DMH properties are investigated. We also study the temperature, frequency and interlayer coupling interaction dependence of the coercive field and remanent magnetization. We compare our results with some theoretical and experimental works and observe a quantitatively good agreement with some theoretical and experimental results.

Hybrid excitations due to crystal field, spin-orbit coupling, and spin waves in LiFePO4

We report on the spin waves and crystal field excitations in single crystal LiFePO$_4$ by inelastic neutron scattering over a wide range of temperatures, below and above the antiferromagnetic transition of this system. In particular, we find extra excitations below $T_N=50$ K that are nearly dispersionless and are most intense around magnetic zone centers. We show that these excitations correspond to transitions between thermally occupied excited states of Fe$^{2+}$ due to splitting of the $S=2$ levels that arise from crystal field and spin-orbit interaction. These excitations are further amplified by the highly distorted nature of the oxygen octahedron surrounding the iron atoms. Above $T_N$, magnetic fluctuations are observed up to at least 720~K, with additional excitation around 4 meV, likely caused by single-ion splittings through spin-orbit and crystal field interactions. The latter weakens slightly at 720~K compared to 100~K, which is consistent with calculated cross-sections using a single-ion model. Our theoretical analysis, using the MF-RPA model, provides both detailed spectra of the Fe $d-$ shell and estimates of the average ordered magnetic moment and $T_N$. By applying the MF-RPA model to a number of existing spin-wave results from other Li$M$PO$_4$ ($M=$ Mn, Co, and Ni), we are able to obtain reasonable predictions for the moment sizes and transition temperatures.

Magnetization plateaus and ground-state phase diagrams of the S=1 Ising model on the Shastry Sutherland lattice

Abstract In this research, we have investigated the magnetic properties of the spin-1 Ising model on the Shastry Sutherland lattice with the crystal field interaction by using the effective-field theory with correlations. The effects of the applied field on the magnetization are examined in detail in order to obtain the magnetization plateaus, thus different types of magnetization plateaus, such as 1/4, 1/3, 1/2, 3/5, 2/3 and 7/9 of the saturation, are obtained for strong enough magnetic fields (h). Magnetization plateaus exhibit single, triple, quintuplet and sextuple forms according to the interaction parameters, hence the magnetization plateaus originate from the competition between the crystal field (D) and exchange interaction parameters (J, J′). The ground-state phase diagrams of the system are presented in three varied planes, namely (h/J, J′/J), (h/J, D/J) and (D/J, J′/J) planes. These phase diagrams display the Neel (N), collinear (C) and ferromagnetic (F) phases for certain values of the model parameters. The obtained results are in good agreement with some theoretical and experimental studies.

High-resolution spectroscopy, crystal-field calculations, and quadrupole helix chirality of DyFe3(BO3)4

High-resolution polarized transmission spectra of DyFe3 (BO3 )4 single crystals were investigated in broad spectral (10-23000 cm−1 ) and temperature (3.5-300 K) ranges. Energies of the dysprosium levels in the paramagnetic and antiferromagnetic phases were determined. On the basis of these data and preliminary calculations in the frameworks of the exchange-charge model, we determined the crystal-field and Dy-Fe exchange interaction parameters of the Dy3 + ions at sites with the point C 2 symmetry corresponding to the enantiomorphic P 31 21 and P 32 21 space groups. The values of electronic quadrupole moments of the Dy3+ ions were calculated, which enabled us to interpret results of the work [Usui et al., Nature Mater. 13, 611 (2014)] on the observation of domains of different quadrupole chirality in DyFe3 (BO3 )4 .

Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes.

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field.

Characterization and magnetic properties of two novel copper(II) coordination polymers prepared by different synthetic techniques

Two novel ternary Cu(II) coordination polymers with formulas {[Cu(μ2-AZPY)(H2BTC)2]}n (1) and {[Cu(μ2-AZPY)(μ2-HBTC)(H2O)]·AZPY}n (2) (AZPY – trans-4,4′-azobis(pyridine), BTC – benzene-1,3,5-tricarboxylate) have been synthesized using the solvothermal or diffusion techniques, respectively. Compounds were characterized by single crystal X-ray diffraction, thermogravimetry, infrared spectroscopy, elemental analysis and AAS. Removal of water and AZPY from the framework of 2 was investigated by wide-angle X-ray scattering measurements during in-situ heating. A magnetic study showed on antiferromagnetic coupling in 1 and 2 and magnetic properties may be influenced by both crystal field (CF) and inter-molecular interactions. The effective magnetic moment decreases from the values μeff=4.97μB for 1 and μeff=3.39μB for 2 at T=290K to the values of μeff=1.41μB for 1 and μeff=1.27μB for 2 at T=2K. The origin of the observed behavior is discussed.

Random crystal field effect on the magnetic and hysteresis behaviors of a spin-1 cylindrical nanowire

In this work, the magnetic behavior of the cylindrical nanowire, consisting of a ferromagnetic core of spin-1 atoms surrounded by a ferromagnetic shell of spin-1 atoms is studied in the presence of a random crystal field interaction. Based on Metropolis algorithm, the Monte Carlo simulation has been used to investigate the effects of the concentration of the random crystal field p, the crystal field D and the shell exchange interaction Js on the phase diagrams and the hysteresis behavior of the system. Some characteristic behaviors have been found, such as the first and second-order phase transitions joined by tricritical point for appropriate values of the system parameters, triple and isolated critical points can be also found. Depending on the Hamiltonian parameters, single, double and para hysteresis regions are explicitly determined.