Sublattice Anisotropy Research Articles

Raman spectroscopy study and dielectric anomalies in Bi1-xEux AFM FeO3 thin films.

BiFeO3 is a multiferroic material, so its ferroelectric and ferromagnetic properties are coupled. Due to the presence of magneto-electric coupling in the system, magnetic changes are obvious in the dielectric spectra. As a thin film of BFO exhibits a weak magnetic moment, dielectric analysis can be utilized to observe different magnetic transitions. In the present work, thin films of Eu3+ substituted BiFeO3 are prepared to stabilize the Perovskite phase. The role of Eu3+ substitution in triggering the structural phase transformation is analyzed using Raman analysis. Capacitance and dissipation spectrum as a function of temperature for various Eu3+ concentrations are studied in detail. The presence of various transitions is observed in the dielectric permittivity. The possible origin of the transitions in permittivity spectra is discussed in terms of spin-lattice and charge interactions and their degrees of freedom. Substitution with rare-earth ions significantly affects the system's magnetic characteristic, including contribution from magnetization from sub-lattice and magnetic anisotropy. Eu3+ substitution led to the change in the spin reorientation axis, which has been explained in terms of phenomenological and microscopic variation in magnetization due to the contribution from the rare earth ion.

Ferrimagnetism in the mean-field approximation of a mixed spin Ising nanowire system

A ferrimagnetic mixed spin square Blume-Capel Ising nanowire system on spin-1 core and spin-3/2 outer shell have been investigated. The general formula for the temperature dependence of the equilibrium magnetization of the system is presented. The ferrimagnetic core-shell nanosystem shows a compensation point when the exchange interactions are changed for different values of the single-ion anisotropies of shell sublattices and core ones, respectively. So, one can examine interesting phenomena are compensation behaviors and the free energy of the nanosystem, where these phenomena found that the mixed-spin square Blume-Capel Ising nanosystem which is being considered has two compensation temperatures in the range of −0.8≤DB|J1|≤−0.4, respectively.

Competition of single-ion anisotropy of Sm and Dy ions during the spin-reorientation transition in (Nd1–x–y Sm x Dy y )(FeCo)B supermagnets

It has been found that an increase in the Sm concentration in the range x = 0.05–0.18 in (Nd1‒x‒ySmxDyy)(FeCo)B supermagnets leads to a shift in the spin-reorientation transition temperature to higher values, whereas a Dy addition results in a decrease in the transition temperature. Single-ion anisotropy of Sm and Dy ions has different symmetry, making contributions of opposite signs to the resulting magnetic anisotropy of the lattice. Therefore, the threshold temperature TS of the spin-reorientation transition, which is determined by the balance of magnetic anisotropies of sublattices, can be controlled using ions with different symmetries.

Spin reorientation and magnetic structure of HoCo12B6 ferrimagnetic compound

The magnetic phase diagram is determined by combining magnetization measurements, ac susceptibility and neutron diffraction. The crystal and magnetic structures are also investigated. The HoCo12B6 compound exhibits ferrimagnetic behavior below TC = 147 K. Two antiferromagnetically coupled sublattices cancel out at the compensation temperature TComp = 46 K. HoCo12B6 undergoes a spin reorientation transition at TSR = 76 K; the easy magnetization axis changes from axial to basal plane upon heating. The magnitude of the magnetic moments and their orientation are described and discussed. It is revealed that HoCo12B6 compound exhibits a commensurate magnetic structure below TSR and an incommensurate one slightly above TSR. Significantly different magnetic moments have been observed on the two Co crystal sites, a very low magnetic moment of 0.14 μB being refined on the Co 18 g position. In addition, the second order crystal electric-field parameter at the rare-earth site is determined. This result is discussed and used to explain the observed spin reorientation transition by a competition between the Co and Ho sublattice anisotropy.

Realising Haldane's vision for a Chern insulator in buckled lattices

The Chern insulator displays a quantum Hall effect with no net magnetic field. Proposed by Haldane over 20 years ago, it laid the foundation for the fields of topological order, unconventional quantum Hall effects, and topological insulators. Despite enormous impact over two decades, Haldane's original vision of a staggered magnetic field within a crystal lattice has been prohibitively difficult to realise. In fact, in the original paper Haldane stresses his idea is probably merely a toy model. I show that buckled lattices with only simple hopping terms, within in-plane magnetic fields, can realise these models, requiring no exotic interactions or experimental parameters. As a concrete example of this very broad, and remarkably simple principle, I consider silicene, a honeycomb lattice with out-of-plane sublattice anisotropy, in an in-plane magnetic field, and show that it is a Chern insulator, even at negligibly small magnetic fields, which is analogous to Haldane's original model.

Monte Carlo simulation of step effect on molecular‐based magnets

AbstractMonte Carlo simulation has been used in detail to study the step effect of the hysteresis loop for a ferrimagnetic mixed spin‐2 and spin‐5/2 Ising model on a honeycomb lattice. The results indicate that the hysteresis loops exhibit an obvious step effect and various shapes for different single‐ion anisotropies and exchange couplings at very low temperature. Under a longitudinal magnetic field (h > 0 or h < 0), we have obtained 2S + 1 magnetic plateaus for different single‐ion anisotropies at low temperature. The existence of triple and double hysteresis loop patterns has been found in the system. It is shown that the sublattice anisotropy and the interlayer exchange coupling strongly affect the coercivity of the system. The influence of the interlayer exchange couplings on the total magnetization, susceptibility, internal energy and specific heat with temperature are numerically examined in the absence of the longitudinal field.

Crystal structure and magnetic properties of Lu 2Co 17− xSi x single crystals

Single crystals of Lu 2Co 17− x Si x within the homogeneity range of Si substitution for Co (0 ≤ x ≤ 3.4) were grown by the Czochralski method. Magnetization measurements have revealed that the parent Lu 2Co 17 compound has a spin-reorientation transition (SRT) from the easy-plane to the easy-axis at elevated temperatures which occurs as 2 second-order phase transitions, the “plane-cone” at T SR1 ≈ 670 K and the “cone-axis” at T SR2 ≈ 730 K. The effect of Si substitution for Co on magnetic anisotropy and spin-reorientations of Lu 2Co 17 was studied. In Lu 2Co 16Si, the SRTs shift towards lower temperatures ( T SR1 ≈ 75 K, T SR2 ≈ 130 K) and disappear for compounds with Si content x > 1 where the anisotropy is uniaxial over the whole range of magnetic ordering. A phenomenological discussion of Co sublattice anisotropy, with reference to the model of individual site contribution to magnetic anisotropy (ISA) is provided.

A neutron diffraction study of the hexagonal pseudo-ternary compounds ErMn 6− xFe xSn 6 ( x = 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0)

The hexagonal ErMn 6− x Fe x Sn 6 solid solution (0.2 < x < 4) has been studied by magnetisation measurements and neutron diffraction. The ordering temperature of the T = (Mn,Fe) sublattice almost continuously increases from T = 386 K for x = 0.2 to T = 498 K for x = 4. The T sublattice orders in the successive magnetic structures helimagnetic H1, antiferromagnetic AF2, helimagnetic H2 and antiferromagnetic AF1 with increasing iron content. While structures AF2 and H1 were already observed in ternary Mn compounds and AF1 in ternary iron compounds, the structure H2 is of a new kind characterized by an AF slab around the Er(1a) site. At low temperature, a change of the easy direction of the Er moment from easy plane to easy axis is observed. The iron-rich compounds display a ferromagnetic order of the Er sublattice. A new kind of magnetic structure characterized by a sine-wave modulated arrangement with a propagating vector Q = (0, 0, q z ) is also observed. The evolution of the magnetic properties (enhancement of the AF character of the (Mn,Fe) sublattice and magnetocrystalline anisotropy of erbium) is discussed.

Study of the magnetostrictive strains in Pr 6Fe 11Ga 3 alloy

Magnetoelastic properties of the Pr 6Fe 11Ga 3 alloy are studied by magnetostriction and thermal expansion measurements. The effects of short- and long-range magnetic ordering processes about Curie temperature clearly appear in the temperature dependence of the spontaneous magnetostriction as two increasing steps with decreasing temperatures. Thermal variations of the total magnetocrystalline anisotropy introduce pronounce changes in the isofield curves of the forced magnetostriction as a negative minimum below 200 K, a compensation phenomena about 250 K, and a positive maximum between 250 K and T c=320 K. The observed behavior of magnetostriction is discussed in terms of the competitive anisotropies of Pr and Fe sublattices and coupling magnetostrictive constants.

Magnetic anisotropy of La0.75Sm0.25Mn2Si2 compound

The magnetic anisotropy of theLa0.75Sm0.25Mn2Si2 compound, whichhas a layered ThCr2Si2-type crystal structure, has been studied using a quasi-single-crystalline sample. It wasfound that the compound possesses a strong uniaxial magnetic anisotropy in bothmagnetically ordered and paramagnetic states. The magnetic anisotropy of the compoundis mainly due to the Mn sublattice anisotropy. In the ferromagnetic state at 180 K,the magnetization process is characterized by the magnetic anisotropy constantK1 = 6 × 106 erg cm−3. In the paramagnetic state, a considerable anisotropy of paramagnetic Curie temperatureΔθp ≈ 35 Kand an appreciable difference between values of the effective magnetic moment measured along thec-axis and in thebasal plane, Δμeff≈0.4 μB per formula unit, has been observed. The natural layered structure of the compound andpartial unquenching of the Mn orbital momentum have been considered as possible reasonsfor the observed strong magnetic anisotropy.

Magnetization studies ofRMn6Ge6−xGaxsingle crystals (R=Sc,Y, Gd–Lu;0.63⩽x⩽1.00)

The magnetic properties of single crystals of rare-earth compounds of composition $R{\mathrm{Mn}}_{6}{\mathrm{Ge}}_{6\ensuremath{-}x}{\mathrm{Ga}}_{x}$ $(x\ensuremath{\approx}1)$ have been studied. In these compounds, the Mn sublattice orders ferromagnetically with a preferred moment direction perpendicular to the $c$ axis. In the compounds in which also the $R$ component carries a magnetic moment, the latter couple antiparallel to the Mn moments. Upon cooling from room temperature to cryogenic temperatures, the $R$-sublattice anisotropy becomes the dominant contribution to the total magnetocrystalline anisotropy, which leads to a spin-reorientation transition at intermediate temperatures for $R=\mathrm{Tb}\ensuremath{-}\mathrm{Yb}$. At low temperatures, the preferred moment directions are characterized by an easy axis for $R=\mathrm{Tb}$, Er, Tm, and Yb and by an easy cone for $R=\mathrm{Dy}$ and Ho. A satisfactory account of the observed preferred moment directions has been given in terms of crystal-field theory. Measurements of the magnetization in the main crystallographic directions have been made in high magnetic fields, up to about 55 T. The interplay between the antiferromagnetic intersublattice $R$-Mn coupling and the magnetocrystalline anisotropy leads to field-induced magnetic phase transitions which are particularly pronounced in the compounds with Ho, Er and Tm.

Spin reorientation in ErCo 10− xFe xMo 2 compounds

The spin reorientation in ErCo 10− x Fe x Mo 2 ( x=0, 1, 2, 3 and 4) compounds has been studied by measurements of the temperature dependence of the magnetization. The spin reorientation in this system is due to the competing anisotropies of the erbium and the transition-metal sublattice. A decrease of the transition-metal sublattice anisotropy is believed to be the reason of the observed increase of the spin-reorientation temperature with increasing Fe content.

Transformations of magnetic phase diagram as a result of insertion of hydrogen and nitrogen atoms in the crystalline lattice of R2Fe17 compounds

The effect of hydrogen and nitrogen insertions on the magnetic properties (Curie temperatures, saturation magnetization, magnetocrystalline anisotropy) of R2Fe17 compounds have been studied. Structural and magnetic investigations have been performed by means of X-ray diffraction, torque and pendulum magnetometer techniques and high-field magnetization measurements on R2Fe17Hx single crystals and on magnetically aligned powder samples of R2Fe17Ny. The hydrides and nitrides still retain the structure of their parent compounds, but the unit cell volumes are expanded. The Curie temperatures are increased by both hydrogenation and nitrogenation. Magnetic phase diagrams of the investigated compounds have been obtained. The effects of the nitrogen and the hydrogen atoms on the rare-earth sublattice anisotropy have been found to be opposite and this is determined by the orientation of the quadrupole moment q of the asymmetric 4f shell with respect to the direction of the resulting magnetic moment of 4f electrons.

Second-order spin reorientation reform in the two-sublattice ferrimagnetic system

Temperature dependence of the spontaneous magnetization and its derivatives reveal the existence of second-order spin reorientation reform (SOSRR) in the two-sublattice ferrimagnetic system. The variation of the competition between two sublattice moments and that between two sublattice anisotropies gives rise to eight types of temperature dependences of the spontaneous magnetization. An example of the phase diagram for the conditions for different types of thermal curves was delineated by means of numerical calculation. Phase diagrams related to SOSRR transitions were depicted by analyzing the exchange-anisotropy flow in the exchange-anisotropy space.

Spin reorientations in La 2− xDy xCo 14B and Y 2− xTb xCo 14B compounds

We have studied the effect of magnetic dilution on the spin-reorientation transition in the tetragonal La 2− x Dy x Co 14B and Y 2− x Tb x Co 14B compounds. Spin orientations in these compounds arise from a competition between the Dy(Tb)-sublattice anisotropy and the Co-sublattice anisotropy. The former dominates at low temperatures, favoring an easy magnetization direction parallel to the c-axis. The latter dominates at high temperatures and favors an easy direction perpendicular to the c-axis. As expected, the spin-reorientation-transition temperature decreases with increasing magnetic dilution. In compounds belonging to the middle concentration range of the La 2− x Dy x Co 14B system, we observed two spin-reorientation-transition temperatures. This has been explained by the occurrence of regions of slightly different Dy concentration. Magnetic phase diagrams have been presented for the La 2− x Dy x Co 14B and Y 2− x Tb x Co 14B systems.

Spin reorientations in La 2− xHo xCo 14B compounds

We have studied the occurrence of spin–reorientation transitions in the tetragonal La 2− x Ho x Co 14B compounds in the concentration range 0.2≤ x≤1.8. Spin orientations in these compounds arise from the competition between the Ho-sublattice anisotropy and the Co sublattice anisotropy. The former dominates at low temperatures, favouring an easy-cone direction of the magnetization at the lowest temperatures followed by an easy magnetization direction parallel to the c-axis at intermediate temperatures. The Co-sublattice anisotropy dominates at high temperatures and favours an easy direction perpendicular to the c-axis. A magnetic phase diagram is presented.

Hydrogenation effects on the magnetic and crystal-field interactions in theR2Fe14BHx(R=Gd,Pr,Dy)compounds

The magnetic properties of the ${R}_{2}{\mathrm{Fe}}_{14}{\mathrm{BH}}_{x}$ $(R=\mathrm{Gd},\mathrm{Pr},$ and Dy) compounds have been studied by measuring low-field ac magnetic susceptibility vs temperature and magnetization vs temperature and applied magnetic field on magnetically aligned samples. A strong reduction in the magnetocrystalline anisotropy of the Gd-based compounds is observed, and the compounds remain axial in the measured temperature range. A hydrogen induced spin reorientation transition (HISRT) takes place in the ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{14}{\mathrm{BH}}_{x}$ series for $x&gt;~1,$ with the transition temperature ${T}_{s}$ increasing with increasing hydrogen content. In the ${\mathrm{Pr}}_{2}{\mathrm{Fe}}_{14}{\mathrm{BH}}_{x}$ compounds no HISRT is found, however for $0&lt;x&lt;~3$ we observe first-order magnetization processes (FOMP), with the critical field ${H}_{c}$ decreasing with increasing hydrogen content. For the ${\mathrm{Pr}}_{2}{\mathrm{Fe}}_{14}{\mathrm{BH}}_{5.5}$ compound the reduction is so strong that ${H}_{c}\ensuremath{\approx}0,$ and the compound remains in a conical phase in the studied temperature range (5 -- 470 K). We have combined analytical methods and a crystalline electric field-mean field model to obtain a quantitative evaluation of the effect of hydrogenation on the magnetic and crystal-field interactions. We have found that the observed behavior in the Gd, Dy, and Pr series can be explained by a decrease of the Fe sublattice anisotropy and by a decrease (in the Dy and Pr series) of the crystal-field parameters ${B}_{n0}$ $(n=2,$ 4, and 6) under hydrogenation. The hydrogen induced variations of the R-Fe exchange interaction seem to have a minor influence on the observed magnetic behavior.

Spin-reorientation and anisotropy of the magnetization in single crystalline Ho 2Co 15Si 2

We have studied the magnetic properties of a Ho 2Co 15Si 2 single crystal. The easy magnetization direction is parallel to the c-axis in an extended temperature region below the Curie temperature. A spin-reorientation transition takes place at 323 K, leading to an easy magnetization direction perpendicular to the c-axis below this temperature. We have compared the present results with those obtained previously on various R 2Co 17 single crystals and found that Si substitution not only leads to a sign reversal in the Co sublattice anisotropy but also leads to a substantial anisotropy of the saturation magnetization. Sign and magnitude of the magnetization anisotropy are conserved during the spin-reorientation transition.

Study of structural and magnetic properties and exchange interactions in (Y 1− xGd x) 3Fe 27.5Ti 1.5 [ x=0, 0.2, 0.5, 0.8, 1.0

The alloys (Y 1− x Gd x ) 3Fe 27.5Ti 1.5 [ x=0, 0.2, 0.5, 0.8, 1.0] were prepared and structurally characterized by the Rietveld analysis of powder X-ray diffraction patterns. The saturation magnetization at 5 K as well as at 300 K monotonically decreased with increasing Gd concentration, due to the antiferromagnetic ordering between the Gd and Fe magnetic moments. The Curie temperature increased from 386 K for x=0 to 525 K for x=1.0. The molecular field coefficients for different exchange interactions were estimated from the mean field analysis of the Curie temperatures of Y 3Fe 27.5Ti 1.5 and Gd 3Fe 27.5Ti 1.5. From these coefficients, the Curie temperatures calculated for the intermediate concentrations were found to agree with the observed values. A Wigner–Seitz cell approach has been employed for the analysis of 57Fe Mössbauer spectra. The average hyperfine fields at 30 and 300 K increased with increase of Gd concentration. The Fe sublattice anisotropy, determined from the XRD of magnetically aligned samples, has planar nature.

Magnetocrystalline anisotropy and magnetostriction of H and N modified R 2Fe 17 compounds (R=Y, Tb, Dy, Ho, Er)

The effects of the hydrogen and the nitrogen on the magnetocrystalline anisotropy (MCA) and magnetostriction of R 2Fe 17M (R=Y, Tb, Dy, Ho, Er; M=H, N) compounds are studied. The signs of the first MCA constants of a rare-earth (R) sublattice are in agreement with the sign of the Stevens factors of R ions for all R 2Fe 17M compounds studied. The effects of the nitrogen and the hydrogen atoms on rare-earth sublattice anisotropy have been found to be opposite. Both hydrogenation and nitrogenation lead to the reduction and change in the signs of the magnetostriction.