Magnetic Reordering Research Articles

Magnetic impurity inducing local defect of polarization and depletion of magnetization in magnetic cluster: blended ferron formation

This paper presents a blended ferron in a ferromagnetic cluster where the electric polarization and magnetization tailor the quasi-particle characteristics. The resulting quasi-particle has coupled acoustic-polaron and ferron characteristics. The constant competition between electric polarization and magnetization alters the effective mass thereby reducing the global inertia of the quasi-particle. The impurity significantly affects the environment, and the resulting defects in the polarization and magnetization are soliton-like. It was observed that any gain in electric polarization is conveyed by a drop in magnetization, where the hybridization of magnetization and polarization gives rise to a new quasi-particle concept: a blended ferron. The latter is manifested by the local deformation of the electric polarization and depletion of the magnetization in the cluster’s signature of magnetic reordering.

External magnetic fields prompting blended ferron magnetization and demagnetization in antiferromagnetic clusters

The paper studies the magnetization and demagnetization of a stable, spin-polarized impurity interacting with phonons and magnons, dubbed blended-ferron in an antiferromagnetic cluster and subjected to an external magnetic field. The weak magnetic field is observed enhance local magnetic reordering and blended-ferron formation. Strong magnetic field enhances ferron demagnetization (with excess spin-down population 0ph,0mag,↓ ) imitating optical polaron characteristics and enhanced ferron magnetization for excess spin-up population 0ph,0mag,↑. For the critical magnetic field, the blended ferron achieves infinite effective mass and exhibits ferromagnetism leading to a spin flop phenomenon. The spin exchange energy is observed to be modified by the phonons which together with the magnons are responsible for the blended-ferron characteristics.

Crystal and Magnetic Structures of the Ternary Ho2Ni0.8Si1.2 and Ho2Ni0.8Ge1.2 Compounds: An Example of Intermetallics Crystallizing with the Zr2Ni1-xP Prototype.

We report two new rare-earth (R) ternary intermetallic compounds—Ho2Ni0.8T1.2 with T = Si and Ge—that correspond to the R5Ni2T3 phase earlier reported to form in Dy–Ni–T and Ho–Ni–T ternary systems. The compounds crystallize in a filled version of the orthorhombic Zr2Ni1–xP-type structure with x = 0.52; their stoichiometry, determined from both single-crystal and powder X-ray diffraction data, is centered on Ho2Ni0.8T1.2 with a narrow solid solubility range for the silicide, while the germanide appears to be a line phase. In addition to R = Dy and Ho, R2Ni0.8T1.2 compounds also form for R = Y and Tb, representing the first examples of rare-earth-based compounds adopting the Zr2Ni1–xP structural prototype. Bulk magnetization data reveal the main transitions of the ferrimagnetic or ferromagnetic type at TC = 38 K for Ho2Ni0.8Si1.2 and TC = 37 K for Ho2Ni0.8Ge1.2, which are followed by subsequent magnetic reordering at lower temperatures. Neutron diffraction shows complex magnetic structures below TC with both ferromagnetic and antiferromagnetic components and magnetic propagation vector κ1 = [0, 0, 0]. Below TN ≅ 24 K (22 K) for the silicide (germanide), an additional antiferromagnetic coupling following an incommensurate magnetic propagation vector κ2 = [κx, 0, 0] appears to coexist with the first magnetic structure.

Nanomagnetism variation with fluorine content in Co(OH)F

Magnetic behaviors of cobalt hydroxide fluoride, Co(OH)F2-x Fx (x = 1.09 and 1.26), which are consisted with nanorods of ∼5 μm length and diameter ∼100 nm, obtained by a facile hydrothermal method, have been researched with the variation of fluorine content as a result of the different amount of reactant NH4F addition. Magnetic coupling performance are characterized based on the observation and analysis of magnetic susceptibility, X-ray Absorption Fine Structure (XAFS) and specific heat. Co(OH)F2-x is found to undergo an antiferromagnetic transition at 40 K. The peak temperature (T) on the transition curves shifts to lower temperature according with the increased magnetic field (H) following the rule of H2/3∞ (-T) because of the surface spin-glass behavior. The paramagnetic susceptibility can be fitted with the modified Curie–Weiss law between 100 K and 320 K. The negative Curie-Weiss temperature indicates that the antiferromagnetic coupling becomes stronger with the fluorine content. In addition, at temperatures below 5 K, the magnetic reordering was observed as spin-glass. Exchange bias behavior in Co(OH)F2-x was found after field cooling process demonstrating an exotic surface magnetic behavior generated with high fluorine contents due to the deformation of CoO6 octahedral induced large spin-glass behavior.

Structural, dielectric, impedance, and modulus spectroscopy of BaSnO3-Modified BiFeO3

A BaSnO3-modified BiFeO3 compound (i.e., Bi0.95Ba0.05Fe0.95Sn0.05O3) was synthesized by a cost-effective mixed-oxide reaction method at 850 °C. The solubility of 5% BaSnO3 in BiFeO3 (BFO) and the formation of a single-phase compound in the rhombohedral structure was checked by the Rietveld refinement method using the X-ray diffraction data. The analysis of Fourier transform infrared (FTIR) spectra reconfirmed the formation of the compound. The temperature-dependent dielectric spectrum for the sample exhibits a broad anomaly at 190 °C, which seems to be the superposition of three Gaussian peaks corresponding to the Maxwell–Wagner effect, as well as the oxygen-vacancy-induced Fe2+/Fe3+ and Sn2+/Sn4+ redox mechanism. A sharp peak at 350 °C corresponds to the magnetic reordering around the Néel temperature. Complex impedance spectroscopy along with modulus analysis confirmed the deviation from Debye-type behavior. The Cole–Cole model was used to resolve the components contributing to the loss tangent. Different models of electrical conduction were used to explain the conduction mechanism in the material. The existence of ferroelectricity in the sample was confirmed from the study of the room-temperature P–E loop. The addition of 5% BaSnO3 to BFO resulted in a 10-fold increase in the dielectric constant and the polarization accompanied by reduced tangent loss, making it attractive for device applications.

Improvement in magnetic parameters of polycrystalline barium hexaferrite by nonmagnetic cation substitution and microwave processing

Polycrystalline ZnZr substituted barium hexaferrite (BaFe12-xZnx/2Zrx/2O19 where x = 0.3, 0.5, 0.7 and 1.0) specimen have been synthesized by two different methods, namely conventional and microwave sintering. The latter has resulted in magnetoplumbite phase in 5 min at a lower temperature (1000 °C). The values of magnetic parameters of different samples are extracted from the corresponding M − H loops using law of approach to saturation magnetization. A high value of saturation magnetization (Ms = 76 emu/g) is obtained for a conventionally sintered sample. Still higher value of saturation magnetization (Ms = 104 emu/g) has been obtained for the microwave sintered cation substituted sample. The increase in the magnetization has been attributed to the magnetic reordering of iron cations in the non-magnetic Zn2+-Zr4+ substituted samples. The coercivity of the microwave processed substituted samples has been drastically reduced to 163 Oe (from 2961 Oe for conventionally sintered pristine sample). The observed decrement can be ascribed to the increase in particle size and reduction in magnetocrystalline anisotropy (2.58 × 106 erg/cc). Raman spectra of the substituted samples have shown a shift in the vibrational frequencies (characteristic of magnetoplumbite phase) with cation substitution. This suggests that the non-magnetic ZnZr cations replace Fe3+ from certain interstitial sites (4f1, 4f2, 2b and 12k).

First principles studies of hydrogen insertion effects on magnetic properties, bonding and structure reordering of UZr2

In the context of the need to recycle depleted uranium coming from nuclear waste, hydrogen absorption in uranium and mainly its alloys is an important solution. We here consider hydrogen insertion in UZr2 intermetallic leading to experimentally observed composition UZr2H6. Drastic changes are shown from density functional calculations to induce atom reordering within the metal substructures in the ground state. Particularly among different starting hypotheses for H sites, energy minimization is observed when the hydrogenated intermetallic undergoes metal substructures reordering with unmixed occupancy of Al (U) and B (Zr) sites in AlB2 type structure. Hydrogen is identified as covalently bonded within the plane of Zr metal, illustrated by anionic charged H−0.55 derived from Bader analysis of charge density. Hydrogen uptake leads to prevailing volume expansion effects versus chemical bonding ones, involving strong localization of uranium 5f states and increased magnetization versus the pristine intermetallic. Both the intermetallic and the ternary hydride are found ferromagnetic in the ground state.

Structural, electrical and magnetic characteristics of improper multiferroic: GdFeO3

Studies of dielectric, impedance, conductivity, magnetic and magneto-electric (ME) properties of GdFeO3 ceramics fabricated by chemical method are reported here. The synthesized powder is phase-pure and crystallizes in the orthorhombic crystal structure. Below 50 °C, the impedance has only grain contribution, while at higher temperatures, it has both grain and grain boundary contributions. Based on the depression angle of the Nyquist plot, the inhomogeneity of the sample is estimated. The capacitance data reveal that at low temperatures, the sample behaves as a leaky capacitor while at higher temperatures the sample shows the effect of the diffusion of thermally excited charge carriers across a barrier. In the low-frequency domain, the dielectric characteristics were explained on the basis of the Maxwell–Wagner mechanism, while in the high-frequency range those were correlated to the grain effect. The frequency dependent characteristic of the tangent loss is explained as a combined contribution from the Debye-like relaxation and dc conductivity related mechanism at higher temperatures. The temperature dependence of the dielectric characteristic and data are found to fit with two Gaussian peaks centered at 148 °C and 169 °C. While the first peak is explained on the basis of the Maxwell–Wagner mechanism, the second has its origin in magnetic reordering and the shifting of Gd3+ ions along the c-axis. The magnetic reordering also results in a sharp decrease of conductivity between 169 °C and 243 °C. The frequency dependent ac conductivity is explained on the basis of the correlated barrier hopping model and the quantum mechanical hopping model for the different frequency domain. The existence of P–E and M–H loops support its improper ferroelectric behavior and canted anti-ferromagnetism respectively. The ME coefficient of the sample is found to be 1.78 mV cm−1 Oe−1.

Multiplex magnetic field annealing evoked remarkable GMI improvement in co-based amorphous wires

We have proposed a series of novel tailoring techniques for integrating conventional vacuum annealing (CVA) and the specific (e.g. transverse- and rotated-) magnetic field annealing (as denoted by TMFA and RMFA respectively), and systematically investigated the impacts of them on the giant magnetoimpedance (GMI) properties and domain microstructure of Co-based amorphous wires. Experimental results indicated that a multiplex MFA treatment i.e, two-step CVA annealing under a rotated magnetic field of 4000Oe, can realize remarkable enhancement of GMI in comparison with the as-prepared, CVA-treated and MFA-treated wires. The GMI ratio increased firstly and then tended to be stable with increasing frequency, moreover, both permeability and GMI ratio decreased with the increase of DC magnetic field. At 13 MHz, the maximum GMI ratio [ΔZ/Zmax]max and field response sensitivity ξmax of RMFA-ed wires increased to 398.39% and 21.84%/Oe, respectively, which is 2.41 times and 3.17 times than those of 165.18% and 6.88%/Oe for the as-prepared wires. Essentially, the physical process of RMFA action is mainly described as the multi-angle induced magnetic anisotropy and atomic reordering dynamic process due to the co-action of rotatory variation magnetic field energy and thermal activation. Meanwhile, the GMI behavior of TMFA evolving from single peak (SP) to double peaks (DPs) is attributed to the increase of magnetic domain driving force (namely domain wall movement increment) and uni-directional inducing magnetic anisotropy at relatively high frequency, which modified the GMI ratio and field sensitivity to 334.61% and 33.51%/Oe, respectively. Therefore, it can be concluded that both RMFA & TMFA would be used to explore microwires with enhanced GMI property for high-performance sensor applications.

Revisiting of Specific Heat of Nonsuperconducting PrBCO Ceramics in Orthorhombic Phase: Signature of Magnetic Phase Transitions at Low Temperatures

The magnetic and electronic contributions of the Pr ions only to the specific heat C p (T) and entropy S(T) defined by ΔC p (T) and ΔS(T), respectively, are revisited at low temperatures for nonsuperconducting PrBa 2 Cu 3 O 6+x ceramics with x = 1 and 0.95. Two small anomalies are observed below the well-known anomaly due to the antiferromagnetic (AFM) ordering of the Pr sublattice at the Neel temperature T N = 17.5 and 14 K, respectively. The first one, which occurs near the transition temperature T 2 ~ 10.5 and ~9.5 K, respectively, is due to the effect of the previous spin reorientation phase transition of the Pr moments. Whereas the second one, which appears for both states at the same critical temperature T cr ~ 4-5 K, is caused by the noncollinear magnetic reordering of the Pr subsystem. A phenomenological analysis is used in the fitting procedure below T cr . The values of the associated electronic linear coefficient Δγ are found for both states fairly lower than those deduced from previous measurements on ceramics and single crystals in orthorhombic phase. In addition to the common T 3 contribution to ΔC p (T), which characterizes the Pr AFM ordering, the T 5 contribution associated with the rather significant Pr-Cu(2) magnetic coupling introduces some nonlinear magnetic effects. All results are discussed and compared with earlier reports.

Revealing orbital and magnetic phase transitions in Pr0.5Ca0.5MnO3 epitaxial thin films by resonant soft x-ray scattering

We report the study of magnetic and orbital order in epitaxial thin films grown on –. Resonant soft x-ray scattering revealed significant modifications of the magnetic order in the film as compared to the bulk. Namely (i) a different magnetic ordering wave vector, (ii) different spin directions and (iii) an additional magnetic reordering transition. We demonstrate that an analysis of the resonant scattering which is based solely on local symmetries and which does not involve a modeling of energy-dependent lineshapes allows to extract this detailed microscopic information. This approach significantly simplifies the analysis and interpretation of resonant scattering data.

Lattice and spin excitations in multiferroich-YbMnO3

Lattice and spin excitations have been studied by Raman scattering in hexagonal YbMnO3 single crystals. The temperature dependences of the phonon modes show that the E2 mode at 256 cm-1 related to the displacement of Mn and O ions in a-b plane is coupled to the spin order. The A1 phonon mode at 678 cm-1 presents a soft mode behavior at the Neel temperature. Connected to the motion of the apical oxygen ions along the c direction, this mode controls directly the Mn-Mn interactions between adjacent Mn planes and the superexchange path. Crystal field and magnon mode excitations have been identified. The temperature investigation of the spin excitations shows that the spin structure is strongly influence by the Yb-Mn interaction. Under a magnetic field along the c axis, we have investigated the magnetic reordering and its impact on the spin excitations.

Thermally induced transition from a ferromagnetic to a paramagnetic state in nanocrystalline FeAl processed by high-pressure torsion

The B2 ordered intermetallic compound FeAl shows a paramagnetic to ferromagnetic transition upon plastic deformation. The magnetic transformation is caused by the formation of a high density of antiphase boundary (APB) tubes leading to an increased number of Fe–Fe nearest neighbour pairs. In the present study it is shown that the temperature of the back transition from the ferromagnetic to the paramagnetic state depends strongly on the deformation mode. FeAl deformed by high pressure torsion (HPT) is investigated by differential scanning calorimetry, transmission electron microscopy and magnetic measurements. Based on the results of FeAl made nanocrystalline and disordered by HPT, it is concluded that the state of ferromagnetism vanishes almost completely at temperatures before re-ordering of the B2 long-range order has been encountered. This is in contrast to the findings reported for ball-milled FeAl indicating that the magnetic back transition and re-ordering occur at the same temperature. A model based on a vacancy driven change of Fe–Fe nearest neighbour configurations is proposed to explain the magnetic back transition after HPT deformation occurring at much lower temperatures.

Mechanical strain characteristics of cold worked Fe 72Al 28 and Fe 75Ni 25 alloys: A positron annihilation coincidence Doppler broadening view

Lattice deformations and texture were induced in Fe 72Al 28 and Fe 75Ni 25 alloys by filing and cold rolling. The deformations and deformation-induced atomic and magnetic domain rearrangements were studied using X-ray diffraction, magnetization measurement and positron annihilation coincidence Doppler broadening spectroscopy. It is observed that both the nonequilibrium processes are generating quite different kinds of atomic and magnetic reordering. In the filed alloys, vacancies are playing major role in manipulating material properties while in the rolled alloys texture is more important. Filing creates much more severe strain than rolling and produces large number of positron trapping centers.

Crystal andmagnetic structure of antiferromagnetic HoAuGe

HoAuGe was prepared from the elements by arc melting and subsequentannealing at 1070 K. Its crystal structure was refined fromsingle-crystal x-ray diffractometer data: a = 440.10(5) pm, c = 723.26(9) pm, V = 0.1213(1) nm3, wR2 = 0.0640, 225F2-values and ten variables. The nuclear structure was confirmedby neutron powder diffraction. HoAuGe adopts the NdPtSb-typestructure. The gold and germanium atoms form two-dimensionalinfinite [AuGe] polyanions with intralayer Au-Ge distances of260.5 pm, while the interlayer Au-Ge distances of 304.1 pm are muchlonger. The polyanions are separated by the holmium ions. Magneticsusceptibility, specific heat capacity and neutron diffractionmeasurements reveal antiferromagnetic ordering at TN = 5.6(2) K with further magnetic reordering at T1 = 3.5(2) K andT2 = 2.4(2) K. At higher temperatures Curie-Weiss behaviour isobserved with µeffexp = 10.2(2) µB andΘp = 0(1) K. From the magnetic specific heat afourfold-degenerate ground state is found. The magnetic structureat 1.3 K is described by the propagation vector k⃗ = (1/2,0,0) withthe Ho spins oriented within the bc-plane. As the temperatureincreases towards TN, the magnetic structure becomesincommensurate, which accounts for the observed additionaltransitions below TN.

Thermodynamic study of the magnetic ordering of Fe3?x Mn x Si alloys

The compounds Fe3−x Mn x Si exhibit a complex magnetic behavior for 0.6⩽x⩽1.75 involving ferromagnetic ordering followed by a reordering at lower temperature. Measurements of the thermal expansion α and the specific heat C p show only a weak anomaly at the Curie temperature, T C, whereas a large, relatively sharp peak occurs at the magnetic reordering temperature, T R. Thermal expansion measurements for the Fe2.2Mn0.8Si compound made about T R are indicative of long-range ordering that can be suppressed in an applied field of ∼0.4T. Magnetization measurements show that low fields, 1–2 mT, strongly influence the bulk magnetization. Irreversible magnetization behavior, similar to that in spin-glass systems, is displayed.

Wavevector and spin-flop transitions in cubic FeGe

Recent neutron diffraction data showing unusual temperature and magnetic-field-induced magnetic reordering in the helical spin-density wave phase of cubic FeFe are analysed in terms of a Landau-type free energy previously used to study related phenomena in isostructural MnSi. The predicted magnetic phase diagrams (H-T) exhibit novel types of first-order and second-order wavevector and spin reorientation phase transitions.

Character of the alpha - beta phase transition in solid oxygen.

Properties of the \ensuremath{\alpha} and \ensuremath{\beta} phases of solid ${\mathrm{O}}_{2}$ are calculated with a deformable-cell Monte Carlo method and the character of the associated phase transition is delineated. We find that the monoclinic \ensuremath{\alpha} phase is stable at temperatures T\ensuremath{\lesssim}18 K and in- and out-of-plane antiferromagnetic order is predicted that is in accord with experiment. The magnetic correlations appear to be long ranged. A phase transition into \ensuremath{\beta}-${\mathrm{O}}_{2}$ occurs at T=17.75\ifmmode\pm\else\textpm\fi{}0.2 K. It is first order with a calculated volume change \ensuremath{\Delta}V=0.06\ifmmode\pm\else\textpm\fi{}0.10 ${\mathrm{cm}}^{3}$/mole, and is accompanied by a magnetic transition into a highly dynamic quasihelical state with a correlation length ${l}_{c}$=8\ifmmode\pm\else\textpm\fi{}1 A\r{} at 18 K, that decreases rapidly with increasing temperature. The results indicate that ${\mathrm{O}}_{2}$ behaves as a two-dimensional magnetic system. The molecular axes exhibit temperature dependent, small angle libration about an axis normal to the basal plane and there is no evidence of precession in \ensuremath{\beta}-${\mathrm{O}}_{2}$. There is also no evidence of magnetic reordering in the \ensuremath{\alpha} phase as a precursor to the transition.

Thermal Expansion of Fe2MnSi

Measurements of the thermal expansion of FezMnSi in the temperature range 200-300 K are reported. A large, relatively narrow peak is found at the magnetic re-ordering temperature in contrast to a broad, weak anomaly at the Curie temperature. Values for the magnetic Gruneisen parameter 'Y m are derived from the thermal expansion data and previously reported specific heat data following the subtraction of a non-magnetic background.

Thermophysical properties of the intermetallic Mn3MN perovskites II. Heat capacity of manganese zinc nitride: Mn3ZnN and manganese gallium nitride: Mn3GaN

Heat-capacity measurements from 5 to 345 K for Mn3ZnN and Mn3GaN are here reported. When one lowers the temperature Mn3ZnN shows two anomalies: the first at TN = (191.4±0.1) K, sharp and narrow, and the second at TA = (127.5±0.1) K. The transitions are due to magnetic ordering and lattice expansion, and to magnetic re-ordering and lattice contraction, respectively. Moreover, both transitions have first-order character. Mn3GaN shows only one anomaly at TN = (278.5±0.1) K, sharp and narrow, due to the magnetic ordering and an abrupt lattice contraction. The equilibrium molar thermodynamic properties at 298.15 K are Cp,m/RSm∘(T)/R{Hm∘(T)−Hm∘(0)}/RK−{Gm∘(T)−Hm∘(0)}/RTMn2ZnN14.5618.8782992.78.841Mn3GaN14.8418.7722965.28.827The analysis of the results below 10 K yields the low-temperature electronic coefficients: γ = (0.022±0.001) J·K−2·mol−1 for Mn3ZnN and γ = (0.038±0.002) J·K−2·mol−1 for Mn3GaN. The existence of a variation in γ in the transition at TA for the Zn compound is clearly derived. For the Ga compound no γ change was detected, but an anomalous electronic contribution was noted.