Antiferromagnetic Phase Transition Research Articles

Ce site dilution effects in the antiferromagnetic heavy fermion CeIn3

La-doped intermetallic single crystals of ${{\mathrm{Ce}}_{1}}_{\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{In}}_{3}$ were synthesized via an In self-flux method throughout the entire range $(x=0--1)$. The prototypical heavy-fermion compound ${\mathrm{CeIn}}_{3}$ shows an antiferromagnetic phase transition at 10.1 K and becomes superconducting near a critical pressure where ${T}_{N}$ is completely suppressed. As the La concentration increases, Ce moments are diluted, and the lattice constant increases linearly, satisfying Vegard's law. The electrical resistivity of the high-quality single crystals of ${{\mathrm{Ce}}_{1}}_{\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{In}}_{3}$ shows a gradual suppression of ${T}_{N}$ to 0 K at approximately ${x}_{c}=0.65$. The sign of the slope of the low-temperature resistivity vs temperature changes from positive to negative in the vicinity of the critical concentration ${x}_{c}$, indicating a change in the Kondo ground states from the Kondo lattice to the Kondo impurity state. In the Kondo lattice state $(x<{x}_{c})$, the coherence temperature $(=50\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ assigned as the peak in the resistivity is almost independent of the La concentration. In the Kondo impurity state $(x>{x}_{c})$, on the other hand, a kinklike feature in the resistivity appears at $\ensuremath{\sim}50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and persists up to $x=0.97$, indicating a change of the Kondo scattering owing to the crystalline electric field effects. These results suggest that the critical concentration is closely connected to the emergence of the Kondo coherence state.

Giant low-field cryogenic magnetocaloric effect in polycrystalline LiErF4 compound

Antiferromagnetic LiErF4 has attracted extensive attention due to its dipolar interaction domination and quantum fluctuations action. In the present work, the crystal structure, cryogenic magnetic properties, and magnetocaloric effect (MCE) of polycrystalline LiErF4 compound are investigated. Crystallographic study shows that the compound crystallizes in the tetragonal scheelite structure with I41/a space group. It exhibits an antiferromagnetic (AFM) phase transition around 0.4 K, accompanied by a giant cryogenic MCE. At 1.3 K, the maximum values of magnetic entropy changes are 24.3 J/kg⋅K, 33.1 J/kg⋅K, and 49.0 J/kg⋅K under the low magnetic field change of 0–0.6 T, 0–1 T, and 0–2 T, respectively. The giant MCE observed above Néel temperature T N is probably due to the strong quantum fluctuations, which cause a large ratio of the unreleased magnetic entropy existing above the phase transition temperature. The outstanding low-field MCE below 2 K makes the LiErF4 compound an attractive candidate for the magnetic refrigeration at the ultra-low temperature.

How electrons Coulomb repulsion changes graphene band structure

Base on effective medium theory we introduce a multi sites method for calculation of realistic energy bands of strongly correlated systems. We found due to approximated self energy, the density of states that obtained directly by calculated local Green function does not reflects system energy bands truly. By using this method we investigated how electrons repulsion renormalizes graphene bands. Graphene realistic bands calculated in both the dynamical mean field theory (DMFT) and four sites beyond super cell approximation for different repulsions. Our calculated interacting graphene bands illustrate a semi metal to a Mott insulator anti ferromagnetic phase transition at repulsions u = 2.2 t and u = 0.6 t for DMFT and four sites beyond super cell approximation respectively. These values are much less than finite size quantum Monte Carlo calculation prediction. We showed that the graphene bands are very sensitive to electrons repulsions and this phase transition happens at low repulsions in comparison to graphene band width.

Anisotropic large magnetoresistance and Fermi surface topology of terbium monoantimonide

Rare-earth monopnictides have received a great deal of attention for their exotic magnetic and electronic properties. Here, we grow high-quality TbSb single crystals, and perform their magnetization, specific heat and transport measurements, and band structure calculations. In this compound, an antiferromagnetic phase transition emerges at ∼14.5 K (TN), below which metamagnetic behaviors can be observed. Specific heat data suggest that Γ4 triplet state dominates the ground magnetic properties, and thus gives rise to weak magnetic anisotropy. Analogous to other isostructural counterparts, TbSb shows extreme magnetoresistance and triangular temperature-field phase diagram. Hall resistivity measurements reveal that carrier concentrations and mobilities change their values in different magnetic states. These findings are supported by the theoretical calculations from which the effect of magnetic orderings on Fermi surface topology can be determined. Nevertheless, the magnetoresistance below and above TN in TbSb shares similar angle dependences, and follows the fashions as observed in those nonmagnetic sister compounds because of its weak anisotropy in magnetization. Our studies uncover the spin ordering effects on angular magnetoresistance and electronic band structures of TbSb, and could be employed to understand the related issues in other systems with similar magnetic behaviors.

Large magnetocaloric effect in Ho2Pd2Pb

We report the magnetocaloric effect (MCE) in a polycrystalline plumbide sample of Ho2Pd2Pb. Arc-melted Ho2Pd2Pb crystallizes in Mo2B2Fe type of tetragonal crystal structure and shows an antiferromagnetic behaviour with Néel temperature of 4.5 K. The Arrott plots indicate that Ho2Pd2Pb undergoes a second order antiferromagnetic phase transition. The calculated isothermal magnetic entropy change (ΔSm), and relative power cooling (refrigeration capacity) for a change of field 0–8 T are 17.8 J kg−1 K−1, and 680(497) J kg−1 respectively. The obtained results revealed that Ho2Pd2Pb belongs to a family of large MCE magnetic materials.

Exact and many-body perturbation solutions of the Hubbard model applied to linear chains

This study reports on the accuracy of the GW approximation for the treatment of the Hubbard model compared to exact diagonalization (ED) results. We consider not only global quantities, such as the total energy and the density of states, but also the spatial and spin symmetry of wavefunctions via the analysis of the local density of states. GW is part of the more general Green’s function approach used to develop many-body approximations. We show that, for small linear chains, the GW approximation corrects the mean-field (MF) approach by reducing the total energy and the magnetization obtained from the MF approximation. The GW energy gap is in better agreement with ED, especially in systems of an even number of atoms where, in contrast to the MF approximation, no plateau is observed below the artificial predicted phase transition. In terms of density of states, the GW approximation induces quasi-particles and side satellite peaks via a splitting process of MF peaks. At the same time, GW slightly modifies the localization (e.g., edges or center) of states. We also use the GW approximation results in the context of Löwdin’s symmetry dilemma and show that GW predicts an artificial paramagnetic–antiferromagnetic phase transition at a higher Hubbard parameter than MF does.

QMC study of the chiral Heisenberg Gross-Neveu universality class

We investigate a quantum criticality of an antiferromagnetic phase transition in the Hubbard model on a square lattice with a d-wave pairing field by large-scale auxiliary-field quantum Monte Carlo simulations. Since the d-wave pairing filed induces Dirac cones in the non-interacting single-particle spectrum, the quantum criticality should correspond to the chiral Heisenberg universality class in terms of the Gross-Neveu theory, which is the same as those expected in the Hubbard model on the honeycomb lattice, despite the unit cells being different (e.g., they contain one and two sites, respectively). We show that both the two phase transitions, expected to occur on the square and on the honeycomb lattices, indeed have the same quantum criticality. We also argue that details of the models, i.e., the way of counting the total number N of fermion components and the anisotropy of the Dirac cones, do not change the critical exponents.

Green Function Treatment of the Barocaloric Effect in Mn3GaN

Following our previous work on the magnetocaloric compounds FeMnAsxP[Formula: see text], we obtain thermomagnetic properties for the barocaloric antiperovskite Mn3GaN, which has been investigated in recent years in view of its thermal response under pressure cycling. Its structure displays canting of spins and a volume dilation in the antiferromagnetic (AFM) transition, related to magnetoelastic coupling. A random-phase-approximation (RPA) Green function theoretical treatment is applied to a two-exchange parameter Heisenberg model, and the canting of the spins orientation in the (111) planes of the structure is considered in the model. The observed first-order AFM phase transitions are reproduced by the introduction of a biquadratic spin term in the Hamiltonian, coupled to the volume dilation in the transition. The model is able to predict a greater stability for the canted spin structure as compared with conventional AFM, if the magnitudes of Mn magnetic moments in these structures are taken from the literature. The calculations of quantities of interest for barocaloric applications reproduce quite well the available data on temperature changes and latent heat under pressure cycling, at adiabatic and isothermal conditions, respectively.

Nature of field-induced antiferromagnetic order in Zn-doped CeCoIn5 and its connection to quantum criticality in the pure compound

Quantum criticality plays an important role in the unconventional nature of superconductivity in strongly correlated electron systems. However, the intrinsic antiferromagnetic (AFM) order parameter responsible for quantum criticality has been unidentified in the prototypical unconventional superconductor ${\mathrm{CeCoIn}}_{5}$. In this work, magnetization and specific-heat measurements for $\mathrm{CeCo}{({\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Zn}}_{x})}_{5}$ with $x\ensuremath{\le}0.07$ demonstrate that the field-induced AFM order develops with Zn doping, along with a continuous increase in its critical field up to 10 T at $x=0.07$. The weak signals associated with the AFM phase transition strongly suggest spatially inhomogeneous evolution of the AFM phase, whose feature becomes pronounced with decreasing the Zn concentration. The temperature, magnetic field, and Zn concentration phase diagram is constructed from those experimental results. It is found that, in this diagram, extrapolating the $x$ dependence of the AFM critical field yields the value of $\ensuremath{\approx}5\phantom{\rule{4pt}{0ex}}\mathrm{T}$ for $x\ensuremath{\rightarrow}0$, which coincides with the location of the quantum critical point in ${\mathrm{CeCoIn}}_{5}$. The specific heat shows $\ensuremath{-}lnT$ diverging behavior characteristic of the non-Fermi-liquid state at the AFM critical fields for all of the $x$ range. The scaling analysis for the specific-heat data above critical fields leads to continuous variations of the scaling parameters as a function of $x$. These findings provide strong evidence that the quantum critical fluctuations in ${\mathrm{CeCoIn}}_{5}$ originate from the order parameter corresponding to the field-induced AFM state observed in Zn-doped systems.

Effect of thermal stress on non-collinear antiferromagnetic phase transitions in antiperovskite Mn3GaN compounds with Mn3SbN inclusions

In the designed (1-x)Mn3GaN-xMn3SbN (0.2 ≤ x ≤ 0.8) heterogeneous system, modulating the non-collinear antiferromagnetic (AFM) phase transitions of antiperovskite Mn3GaN using thermal stress is realized for the first time. With growing the Mn3SbN secondary phase, the Neel temperature (TN) of Mn3GaN phase shifts down by 40 K and then disappears, but another magnetic transition below TN appears and shifts up by 125 K. The neutron powder diffraction (NPD) results of the sample with x = 0.6 show that the magnetic transition below TN ascribed to the decreasing Mn–Mn distance (dMn–Mn) and spin re-orientation from Γ5g to a new non-collinear M2 AFM phase. By the NPD analysis, the dMn–Mn of the Mn3GaN phase decreases from 2.75527(4) Å to 2.73925(3) Å, and the angles of the spin rotations for Mn1/Mn2, Mn3-1, and Mn3-2 atoms in M2 AFM during the spin re-orientation process are 90°, 60°, and 60°, respectively. Negative thermal expansion behaviors and caloric effects associated with Γ5g phase transitions are investigated systematically. Further, the thermal stress could be regulated by adjusting the proportion of Mn3GaN and Mn3SbN phases with mismatched thermal expansion, which could be estimated even up to GPa according to Clausius–Clapeyron relation.

Effect of Dzyaloshinskii-Moriya Interaction on Heisenberg Antiferromagnetic Spin Chain in the Presence of a Longitudinal Magnetic Field

Using functional integral method for the Heisenberg antiferromagnetic spin chain with the added Dzyaloshinskii-Moriya Interaction in the presence of the longitudinal magnetic field, we find out expression for free energy of the spin chain via spin fluctuations, from which quantities characterize the antiferromagnetic order and phase transition such as staggered and total magnetizations derived. From that, we deduce the significant effect of the Dzyaloshinskii-Moriya interaction on the reduction of the antiferromagnetic order and show that the total magnetization can be deviated from the initial one under the influence of canting of the spins due to a combination of the Dzyaloshinskii-Moriya interaction and the magnetic field. Besides, the remarkable role of the transverse spin fluctuations due to the above factors on the antiferromagnetic behaviours of the spin chain is also indicated.

Small-moment antiferromagnetic ordering in single-crystalline La2Ni7

Single crystals of La2Ni7 have been grown out of a binary, La-Ni melt. Temperature dependent, zero magnetic field, specific heat, electrical resistivity, and low field magnetization measurements indicate that there is a series of antiferromagnetic phase transitions at T1 = 61.0 \pm 0.2 K, T2 = 56.5 \pm 0.2 K and T3 = 42.2 \pm 0.2 K. The three specific heat anomalies found at these temperatures qualitatively have very small entropy changes associated with them and the anisotropic M(H) data saturate at ~ 0.12 {\mu}B/Ni; both observations strongly suggesting the AFM order is associated with very small, itinerant, moments. Anisotropic, H||c and H{\perp}c, {\rho}(H) and M(H) isotherms as well as constant field, {\rho}(T) and M(T) sweeps manifest signatures of multiple phase lines and result in H-T phase diagrams that are clearly anisotropic. Analysis of M(T) and M(H) data allow for the identification of the two lower temperature magnetically ordered states as antiferromagnetically ordered, with the moments aligned along the crystallographic c-axis, and the higher temperature, T2 < T < T1, state as having a finite ferromagnetic component. In addition, the metamagnetic transition at low temperatures, for H applied along the crystallographic c-axis (H||c) appears to be a near classic example of a spin-flop transition, resulting in a field stabilized antiferromagnetic state with the moments ordered perpendicular to the c-axis. Although the small moment ordering, and existence of multiple phase transitions in field and temperature, suggesting an energetic proximity of these states, could foretell a degree of pressure sensitivity, our measurements of R(T) for applied pressures up to 2.0 GPa indicate that there is very little pressure dependence of T1, T2 and T3.

Electrical and Magnetic Properties of SmSb Single Crystals at Low Temperatures

On SmSb single crystals synthesized from elements, the electrical resistance R and magnetization M were measured as functions of temperature and magnetic field. A large magnetoresistance is observed over the entire temperature range of 2-300 K, increasing significantly with decreasing temperature. The temperature dependence of the magnetization exhibits a singularity at the transition temperature to the antiferromagnetic state TN=2.3 K. At temperatures below 8 K, de Haas--van Alphen oscillations are observed in the M(H) dependences, the frequencies of which do not change upon the transition through TN. Linear extrapolation of the dependence of the Landau indices N on the reciprocal of the magnetic field 1/B to zero gives the value NT=2 K=0.75, which indicates the presence of the Berry phase and a nontrivial band topology in the SmSb compound. Keywords: samarium monoantimonide, magnetization, magnetoresistance, antiferromagnetic phase transition, de Haas-van Alphen magnetic oscillations, Berry phase.

Теплофизические свойства мультиферроиков Bi-=SUB=-1-x-=/SUB=-Tm-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

Investigations of the heat capacity, thermal diffusivity, and thermal conductivity of multiferroics Bi1-xTmxFeO3 (x = 0, 0.05, 0.10, 0.20) have been carried out in the high temperature range of 300-1200 K. and thermal conductivity in the region of phase transitions. The temperature dependences of the specific heat for compositions with x = 0.10 and 0.20 exhibit an additional anomaly characteristic of the phase transition at T = 580 K. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions are considered. The temperature dependence of the average phonon mean free path is determined.

Thermophysical properties of multiferroics Bi-=SUB=-1-x-=/SUB=-Tm-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

Investigations of the heat capacity, thermal diffusivity, and thermal conductivity of multiferroics Bi1-xTmxFeO3 (x=0, 0.05, 0.10, 0.20) have been carried out in the high temperature range of 300-1200 K. and thermal conductivity in the region of phase transitions. The temperature dependences of the specific heat for compositions with x=0.10 and 0.20 exhibit an additional anomaly characteristic of the phase transition at T=580 K. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions are considered. The temperature dependence of the average phonon mean free path is determined. Keywords: multiferroics, heat capacity, thermal diffusivity, thermal conductivity.

Antiferromagnetic quaternary chalco-halide Ba3(FeS4)I with long Fe⋯Fe distances

A new chalco-halide Ba3(FeS4)I was synthesized, which shows a remarkable antiferromagnetic phase transition at 108 K realized by the novel Fe–S⋯S–Fe super–super exchanges.

Tunable Strong Coupling of Mechanical Resonance between Spatially Separated FePS3 Nanodrums.

Coupled nanomechanical resonators made of two-dimensional materials are promising for processing information with mechanical modes. However, the challenge for these systems is to control the coupling. Here, we demonstrate strong coupling of motion between two suspended membranes of the magnetic 2D material FePS3. We describe a tunable electromechanical mechanism for control over both the resonance frequency and the coupling strength using a gate voltage electrode under each membrane. We show that the coupling can be utilized for transferring data between drums by amplitude modulation. Finally, we also study the temperature dependence of the coupling and how it is affected by the antiferromagnetic phase transition characteristic of this material. The presented electrical coupling of resonant magnetic 2D membranes holds the promise of transferring mechanical energy over a distance at low electrical power, thus enabling novel data readout and information processing technologies.

Structural, vibrational, thermal, and magnetic properties of mullite‐type NdMnTiO5 ceramic

AbstractMullite‐type RMn2O5 (R = Y, rare‐earth element) ceramics are of ongoing research attention because of their interesting crystal‐chemical and magnetic properties. We report nuclear and magnetic structures of NdMnTiO5 together with its spectroscopic, thermogravimetric, and magnetic properties. The polycrystalline sample is prepared by solid‐state synthesis and characterized from neutron and X‐ray powder diffraction data Rietveld refinements. NdMnTiO5 crystallizes in the orthorhombic space group Pbam with metric parameter a = 755.20(1) pm, b = 869.91(1) pm, c = 582.42(1) pm, and V = 382.62(1) 106 pm3. The Mn3+ and Ti4+ cations are observed to be located in the octahedral and pyramidal sites, respectively. The vibrational features in these polyhedral sites are characterized by Raman and Fourier transform infrared spectroscopes. The higher decomposition temperature of NdMnTiO5, compared to other RMn2O5 phases, is explained in terms of the higher bond strength of Ti‐O bonds than those of Mn‐O bonds. Temperature‐dependent DC magnetic susceptibility suggests a paramagnetic to antiferromagnetic phase transition at 43(1) K. Inverse susceptibility in the paramagnetic region above 120 K follows the Curie‐Weiss law, resulting in a magnetic moment of 6.33(1) μB per formula unit. Neutron diffraction data collected at 7.5 K reveal that the magnetic moments of Nd3+ and Mn3+ in NdMnTiO5 are incommensurately ordered with a propagation vector k = (0, 0.238, 0.117).

Spin dynamics of the spin-chain antiferromagnet RbFeS2

We report transport and inelastic neutron scattering studies on electronic properties and spin dynamics of the quasi-one-dimensional spin-chain antiferromagnet ${\mathrm{RbFeS}}_{2}$. An antiferromagnetic phase transition at ${T}_{N}\ensuremath{\approx}195$ K and dispersive spin waves with a spin gap of 5 meV are observed. By modeling the spin excitation spectra using linear spin wave theory, intra and interchain exchange interactions are found to be $S{J}_{1}=100(5)$ meV and $S{J}_{3}=0.9(3)$ meV, respectively, together with a small single-ion anisotropy of $S{D}_{zz}=0.04(1)$ meV. Comparison with previous results for other materials in the same class of ${\mathrm{Fe}}^{3+}$ spin-chain systems reveals that although the magnetic order sizes show significant variation from 1.8 to $3.0\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$ within the family of materials, the exchange interactions $SJ$ are nevertheless quite similar, analogous to the iron pnictide superconductors where both localized and delocalized electrons contribute to the spin dynamics.

Colossal Magnetoresistance in Ti Lightly Doped Cr2Se3 Single Crystals with a Layered Structure.

Stoichiometric Cr2Se3 single crystals are particular layer-structured antiferromagnets, which possess a noncollinear spin configuration, weak ferromagnetic moments, moderate magnetoresistance (MR ∼14.3%), and poor metallic conductivity below the antiferromagnetic phase transition. Here, we report an interesting >16 000% colossal magnetoresistance (CMR) effect in Ti (1.5 atomic percent) lightly doped Cr2Se3 single crystals. Such a CMR is approximately 1143 times larger than that of the stoichiometric Cr2Se3 crystals and is rarely observed in layered antiferromagnets and is attributed to the frustrated spin configuration. Moreover, the Ti doping not only dramatically changes the electronic conductivity of the Cr2Se3 crystal from a bad metal to a semiconductor with a gap of ∼15 meV but also induces a change in the magnetic anisotropy of the Cr2Se3 crystal from strong out-of-plane to weak in-plane. Further, magnetotransport measurements reveal that the low-field MR scales with the square of the reduced magnetization, which is a signature of CMR materials. The layered Ti:Cr2Se3 with the CMR effect could be used as two-dimensional (2D) heterostructure building blocks to provide colossal negative MR in spintronic devices.