In-plane Magnetic Susceptibility Research Articles

A Significant Two-Dimensional Structural Transformation in a Coordination Polymer that Changes Its Electronic and Protonic Behavior.

A 2D-to-2D (2D: two-dimensional) structural transformation accompanying significant bond rearrangement and coordination environment change is demonstrated in a coordination polymer (CP) comprised of copper(II) ions and terephthalate (BDC2- ) ligands for the first time. When immersed in water, a free-standing membrane of 2D Cu(BDC)(DMF) (Cu-1; DMF: N,N-dimethylformamide) transforms into 2D Cu(BDC)(H2 O)2 (Cu-2) while maintaining its highly oriented layered structure. In the 2D sheet, paddlewheel-type CuII dimers coordinated with four bidentate BDC ligands in a square-planar array in Cu-1 were released to form uniform aqua-bridged CuII chains, which are cross-linked with each other by unidentate BDC ligands, in Cu-2. The present facile approach to implement the 2D-to-2D transformation accompanied by bond rearrangement, which is characteristic of CPs, leads to a marked increase in in-plane magnetic susceptibility and proton conductivity. In situ experiments in support of theoretical calculations unveiled the energy diagram that governs the unique structural transformation.

Anisotropic magnetotransport properties coupled with spiral spin modulation in a magnetic semimetal EuZnGe

We investigate the thermodynamic, magnetic, and electrical transport properties of a triangular-lattice antiferromagnet EuZnGe using single crystals grown from Eu-Zn flux in sealed tantalum tubes. Magnetic properties are found to be isotropic in the paramagnetic state while we observe an enhancement of in-plane magnetic susceptibility at the temperature near T* =11.3 K, suggesting an easy-plane anisotropy at low temperatures. Magnetic transition temperature is lower than T* as specific heat shows a peak at TN =7.6 K. We reveal the magnetic modulation along the c axis by resonant x-ray scattering at Eu L2 edge, which suggests competing magnetic interaction among Eu triangular-lattice layers. We observe a double-peak structure in the intensity profile along (0, 0, L) below TN, which is mainly composed of a dominant helical modulation with q ~ (0, 0, 0.4) coexisting with a secondary contribution from q ~ (0, 0, 0.5). We reproduce the intensity profile with a random mixture of five- and four-sublattice helices with spin rotation skipping due to hexagonal in-plane anisotropy. The metallic conductivity is highly anisotropic with the ratio rho_zz/rho_xx exceeding 10 over the entire temperature range and additionally exhibits a sharp enhancement of rho_zz at TN giving rise to rho_zz/rho_xx ~ 50, suggesting a coupling between out-of-plane electron conduction and the spiral magnetic modulations. In-plane magnetic field induces a spin-flop like transition, where the q = 0.4 peak disappears and an incommensurate peak of approximately qICM ~ 0.47 emerges, while the q = 0.5 modulation retains a finite intensity. This transition correlates with non-monotonic magnetoresistance and Hall resistivity, suggesting a significant interplay between electrons and spin structures through Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction.

Long-Time Magnetic Relaxation in Antiferromagnetic Topological Material EuCd2As2 Supported by the National Key Research and Development Program of China (Grant Nos. 2016YFA0300600 and 2018YFA0305600), the National Natural Science Foundation of China (Grant No. 11974404), the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB33000000), and the Youth Innovation Promotion Association of CAS (Grant No. 2017013).

Magnetic topological materials have attracted much attention due to the correlation between topology and magnetism. Recent studies suggest that EuCd2As2 is an antiferromagnetic topological material. Here by carrying out thorough magnetic, electrical and thermodynamic property measurements, we discover a long-time relaxation of the magnetic susceptibility in EuCd2As2. The (001) in-plane magnetic susceptibility at 5 K is found to continuously increase up to ∼10% over the time of ∼14 hours. The magnetic relaxation is anisotropic and strongly depends on the temperature and the applied magnetic field. These results will stimulate further theoretical and experimental studies to understand the origin of the relaxation process and its effect on the electronic structure and physical properties of the magnetic topological materials.

Highly anisotropic excitons and multiple phonon bound states in a van der Waals antiferromagnetic insulator.

Two-dimensional (2D) semiconductors enable the investigation of light-matter interactions in low dimensions1,2. Yet, the study of elementary photoexcitations in 2D semiconductors with intrinsic magnetic order remains a challenge due to the lack of suitable materials3,4. Here, we report the observation of excitons coupled to zigzag antiferromagnetic order in the layered antiferromagnetic insulator NiPS3. The exciton exhibits a narrow photoluminescence linewidth of roughly 350 μeV with near-unity linear polarization. When we reduce the sample thickness from five to two layers, the photoluminescence is suppressed and eventually vanishes for the monolayer. This suppression is consistent with the calculated bandgap of NiPS3, which is highly indirect for both the bilayer and the monolayer5. Furthermore, we observe strong linear dichroism (LD) over a broad spectral range. The optical anisotropy axes of LD and of photoluminescence are locked to the zigzag direction. Furthermore, their temperature dependence is reminiscent of the in-plane magnetic susceptibility anisotropy. Hence, our results indicate that LD and photoluminescence could probe the symmetry breaking magnetic order parameter of 2D magnetic materials. In addition, we observe over ten exciton-A1g-phonon bound states on the high-energy side of the exciton resonance, which we interpret as signs of a strong modulation of the ligand-to-metal charge-transfer energy by electron-lattice interactions. Our work establishes NiPS3 as a 2D platform for exploring magneto-exciton physics with strong correlations.

Electronic, magnetic, and thermodynamic properties of the kagome layer compound FeSn

Single crystals of the single Kagome layer compound FeSn are investigated using x-ray and neutron scattering, magnetic susceptibility and magnetization, heat capacity, resistivity, Hall, Seebeck, thermal expansion, thermal conductivity measurements and density functional theory (DFT). FeSn is a planar antiferromagnet below TN = 365 K and exhibits ferromagnetic magnetic order within each Kagome layer. The in-plane magnetic susceptibility is sensitive to synthesis conditions. Resistivity, Hall and Seebeck results indicate multiple bands near the Fermi energy. The resistivity of FeSn is about 3 times lower for current along the stacking direction than in the plane, suggesting that transport and the bulk electronic structure of FeSn is not quasi 2D. FeSn is an excellent metal with Rho(300K)/Rho(2K) values about 100 in both directions. While the ordered state is antiferromagnetic, high temperature susceptibility measurements indicate a ferromagnetic Curie-Weiss temperature of 173 K, reflecting the strong in-plane ferromagnetic interactions. DFT calculations show a 3D electronic structure with the Dirac nodal lines along the K-H directions in the magnetic Brillouin zone about 0.3 eV below the Fermi energy, with the Dirac dispersions at the K points gapped by spin-orbit coupling except at the H point. The magnetism, however, is highly 2D with Jin-plane/Jout-of-plane = 10. The predicted spin-wave spectrum is presented.

Enhanced moments of Eu in single crystals of the metallic helical antiferromagnetEuCo2−yAs2

The compound EuCo{2-y}As2 with the tetragonal ThCr2Si2 structure is known to contain Eu{+2} ions with spin S = 7/2 that order below a temperature TN = 47 K into an antiferromagnetic (AFM) proper helical structure with the ordered moments aligned in the tetragonal ab plane, perpendicular to the helix axis along the c axis, with no contribution from the Co atoms. Here we carry out a detailed investigation of the properties of single crystals. Enhanced ordered and effective moments of the Eu spins are found in most of our crystals. Electronic structure calculations indicate that the enhanced moments arise from polarization of the d bands, as occurs in ferromagnetic Gd metal. Electrical resistivity measurements indicate metallic behavior. The low-field in-plane magnetic susceptibilities chi{ab}(T < TN) for several crystals are reported that are fitted well by unified molecular field theory (MFT), and the Eu-Eu exchange interactions Jij are extracted from the fits. High-field magnetization M data for magnetic fields H||ab reveal what appears to be a first-order spin-flop transition followed at higher field by a second-order metamagnetic transition of unknown origin, and then by another second-order transition to the paramagnetic (PM) state. For H||c, the magnetization shows only a second-order transition from the canted AFM to the PM state, as expected. The critical fields for the AFM to PM transition are in approximate agreement with the predictions of MFT. Heat capacity Cp measurements in zero and high H are reported. Phase diagrams for H||c and H||ab versus T are constructed from the high-field M(H,T) and Cp(H,T) measurements. The magnetic part Cmag(T, H = 0) of Cp(T, H = 0) is extracted and is fitted rather well below TN by MFT, although dynamic short-range AFM order is apparent in Cmag(T) up to about 70 K, where the molar entropy attains its high-T limit of R ln8.

Evidence for short-range magnetic order in the nematic phase of FeSe from anisotropic in-plane magnetostriction and susceptibility measurements

The nature of the nematic state in FeSe remains one of the major unsolved mysteries in Fe- based superconductors. Both spin and orbital physics have been invoked to explain the origin of this phase. Here we present experimental evidence for frustrated, short-range magnetic order, as suggested by several recent theoretical works, in the nematic state of FeSe. We use a combination of magnetostriction, susceptibility and resistivity measurements to probe the in-plane anisotropies of the nematic state and its associated fluctuations. Despite the absence of long-range magnetic order in FeSe, we observe a sizable in-plane magnetic susceptibility anisotropy, which is responsible for the field-induced in-plane distortion inferred from magnetostriction measurements. Further we demonstrate that all three anisotropies in FeSe are very similar to those of BaFe2As2, which strongly suggests that the nematic phase in FeSe is also of magnetic origin.

Dichotomy between in-plane magnetic susceptibility and resistivity anisotropies in extremely strained BaFe2As2

High-temperature superconductivity in the Fe-based materials emerges when the antiferromagnetism of the parent compounds is suppressed by either doping or pressure. Closely connected to the antiferromagnetic state are entangled orbital, lattice, and nematic degrees of freedom, and one of the major goals in this field has been to determine the hierarchy of these interactions. Here we present the direct measurements and the calculations of the in-plane uniform magnetic susceptibility anisotropy of BaFe2As2, which help in determining the above hierarchy. The magnetization measurements are made possible by utilizing a simple method for applying a large symmetry-breaking strain, based on differential thermal expansion. In strong contrast to the large resistivity anisotropy above the antiferromagnetic transition at TN, the anisotropy of the in-plane magnetic susceptibility develops largely below TN. Our results imply that lattice and orbital degrees of freedom play a subdominant role in these materials.

Feasibility of real-time MR thermal dose mapping for predicting radiofrequency ablation outcome in the myocardium in vivo

BackgroundClinical treatment of cardiac arrhythmia by radiofrequency ablation (RFA) currently lacks quantitative and precise visualization of lesion formation in the myocardium during the procedure. This study aims at evaluating thermal dose (TD) imaging obtained from real-time magnetic resonance (MR) thermometry on the heart as a relevant indicator of the thermal lesion extent.MethodsMR temperature mapping based on the Proton Resonance Frequency Shift (PRFS) method was performed at 1.5 T on the heart, with 4 to 5 slices acquired per heartbeat. Respiratory motion was compensated using navigator-based slice tracking. Residual in-plane motion and related magnetic susceptibility artifacts were corrected online. The standard deviation of temperature was measured on healthy volunteers (N = 5) in both ventricles. On animals, the MR-compatible catheter was positioned and visualized in the left ventricle (LV) using a bSSFP pulse sequence with active catheter tracking. Twelve MR-guided RFA were performed on three sheep in vivo at various locations in left ventricle (LV). The dimensions of the thermal lesions measured on thermal dose images, on 3D T1-weighted (T1-w) images acquired immediately after the ablation and at gross pathology were correlated.ResultsMR thermometry uncertainty was 1.5 °C on average over more than 96% of the pixels covering the left and right ventricles, on each volunteer. On animals, catheter repositioning in the LV with active slice tracking was successfully performed and each ablation could be monitored in real-time by MR thermometry and thermal dosimetry. Thermal lesion dimensions on TD maps were found to be highly correlated with those observed on post-ablation T1-w images (R = 0.87) that also correlated (R = 0.89) with measurements at gross pathology.ConclusionsQuantitative TD mapping from real-time rapid CMR thermometry during catheter-based RFA is feasible. It provides a direct assessment of the lesion extent in the myocardium with precision in the range of one millimeter. Real-time MR thermometry and thermal dosimetry may improve safety and efficacy of the RFA procedure by offering a reliable indicator of therapy outcome during the procedure.

Ground-state properties of the triangular-lattice Heisenberg antiferromagnet with arbitrary spin quantum number s

We apply the coupled cluster method to high orders of approximation and exact diagonalizations to study the ground-state properties of the triangular-lattice spin-s Heisenberg antiferromagnet. We calculate the fundamental ground-state quantities, namely, the energy e0, the sublattice magnetization Msub, the in-plane spin stiffness ρs and the in-plane magnetic susceptibility χ for spin quantum numbers s=1/2,1,…,smax, where smax=9/2 for e0 and Msub, smax=4 for ρs and smax=3 for χ. We use the data for s≥3/2 to estimate the leading quantum corrections to the classical values of e0, Msub, ρs, and χ. In addition, we study the magnetization process, the width of the 1/3 plateau as well as the sublattice magnetizations in the plateau state as a function of the spin quantum number s.

In-Plane Transverse Susceptibility of (111)-Oriented Iron Garnet Films

Iron garnet films with various compositions Y3Fe5O12 (YIG), (LuPr)3Fe5O12 (LuPrIG), and Tm3(FeSc)5 O 12 (TmScIG) were grown by liquid phase epitaxy on gadolinium gallium garnet substrates. The angular dependences of in-plane transverse magnetic susceptibility $\chi ^\prime $ ( $\varphi $ ) were investigated to estimate their applicability as a fluxgate core. The $\chi ^\prime $ ( $\varphi $ ) dependence permitted the determination of the anisotropy field ${H}_{C}$ in the film plane. Experimentally obtained values of ${H}_{C}$ show good agreement with theoretical values and correspond to 2.5, 0.92, and 0.03 Oe for YIG, LuPrIG, and TmScIG epitaxial films, respectively. The influence of garnet composition on mechanisms of decreasing of induced in-plane anisotropy field was determined. TmScIG films exhibit about 100-fold reduction in the anisotropy in the plane of the film as compared with films of pure YIG.

Cyclotron Resonance in the Hidden-Order Phase ofURu2Si2

We report the first observation of cyclotron resonance in the hidden-order phase of ultraclean URu2Si2 crystals, which allows the full determination of angle-dependent electron-mass structure of the main Fermi-surface sheets. We find an anomalous splitting of the sharpest resonance line under in-plane magnetic-field rotation. This is most naturally explained by the domain formation, which breaks the fourfold rotational symmetry of the underlying tetragonal lattice. The results reveal the emergence of an in-plane mass anisotropy with hot spots along the [110] direction, which can account for the anisotropic in-plane magnetic susceptibility reported recently. This is consistent with the "nematic" Fermi liquid state, in which itinerant electrons have unidirectional correlations.

Weakly ferromagnetic metallic state in heavily doped Ba1−xKxMn2As2

Heavily doped Ba${}_{1\ensuremath{-}x}$K${}_{x}$Mn${}_{2}$As${}_{2}$ ($x=0.19$ and 0.26) single crystals were successfully grown and investigated by the measurements of resistivity and anisotropic magnetization. In contrast to the antiferromagnetic insulating ground state of the undoped BaMn${}_{2}$As${}_{2}$, the K-doped crystals show metallic conduction with weak ferromagnetism below $\ensuremath{\sim}$50 K and Curie--Weiss-like in-plane magnetic susceptibility above $\ensuremath{\sim}$50 K. Under high pressures up to 6 G Pa, the low-temperature metallicity changes into a state characterized by a Kondo-like resistivity minimum. Electronic structure calculations for $x=0.25$ using a $2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}1$ supercell reproduce the hole-doped metallic state. The density of states at Fermi energy has significant As-4$p$ components, indicating that the 4$p$ holes are mainly responsible for the metallic conduction. Our results suggest that the interplay between the itinerant 4$p$ holes and the local 3$d$ moments is mostly responsible for the novel metallic state.

Quasi-Two-Dimensional Fermi-Liquid State in Sr2RhO4-δ

Single crystals of layered perovskite Sr 2 RhO 4-δ (δ=0.0 and 0.1) are successfully grown by the floating-zone method. Stoichiometric single crystals (Sr 2 RhO 4.0 ) are obtained by O 2 -annealing the as-grown crystals (Sr 2 RhO 3.9 ). Sr 2 RhO 4.0 and Sr 2 RhO 3.9 show quasi-two-dimensional Fermi-liquid behavior at low temperatures, whereas there are large differences in the anisotropy of electrical resistivity ρ c (3 K)/ρ a b (3 K) and Wilson ratio R w between Sr 2 RhO 4.0 and Sr 2 RhO 3.9 : ρ c (3 K)/ρ a b (3 K) = 2400 (19000) and R w =3.8 (6.4) for Sr 2 RhO 4.0 (Sr 2 RhO 3.9 ). The differences observed between the temperature dependence of the in-plane electrical resistivity ( T <15 K), magnetic susceptibility ( T <300 K) and specific heat ( T <10 K) of Sr 2 RhO 4.0 and Sr 2 RhO 3.9 are mainly derived from those between the density of states and band structure near the corresponding Fermi level. This indicates that the changes in these physical properties, which are accompanied by oxygen defects in th...

Considerable nonlocal electronic correlations in strongly dopedNaxCoO2

The puzzling electronic correlation effects in the sodium cobaltate system are studied by means of the combination of density functional theory and the rotationally invariant slave boson (RISB) method in a cellular-cluster approach. Realistic non-local correlations are hence described in the short-range regime for finite Coulomb interactions on the underlying frustrated triangular lattice. A local Hubbard U is sufficient to model the gross in-plane magnetic behavior with doping x, namely antiferromagnetic correlations at intermediate doping and the onset of ferromagnetic order above x>3/4 with a mixed phase for 0.62<x<3/4. Important insight is thereby provided by the occupations of local cluster multiplets retrieved from the RISB framework. The extended modeling of the x$\ge$2/3 doping regime with an additional inter-site Coulomb repulsion V on an experimentally verified effective kagom\'e lattice allows to account for relevant charge-ordering physics. Therewith a fluctuating charge-density-wave state with small quasiparticle weight and a maximum in-plane magnetic susceptibility may be identified at x$\sim$3/4, just where the magnetic ordering sets in.

High-order coupled cluster method study of frustrated and unfrustrated quantum magnetsin external magnetic fields

We apply the coupled cluster method (CCM) in order to study the ground-state propertiesof the (unfrustrated) square-lattice and (frustrated) triangular-lattice spin-half Heisenbergantiferromagnets in the presence of external magnetic fields. Approximate methods aredifficult to apply to the triangular-lattice antiferromagnet because of frustration, and so,for example, the quantum Monte Carlo (QMC) method suffers from the ‘signproblem’. Results for this model in the presence of magnetic field are rarer thanthose for the square-lattice system. Here we determine and solve the basic CCMequations by using the localized approximation scheme commonly referred to as the ‘LSUBm’ approximation scheme and we carry out high-order calculations by using intensivecomputational methods. We calculate the ground-state energy, the uniform susceptibility,the total (lattice) magnetization and the local (sublattice) magnetizations as a functionof the magnetic field strength. Our results for the lattice magnetization of thesquare-lattice case compare well to the results from QMC approaches for all values of theapplied external magnetic field. We find a value for the magnetic susceptibility ofχ = 0.070 for thesquare-lattice antiferromagnet, which is also in agreement with the results from other approximate methods(e.g., χ = 0.0669 obtained via the QMC approach). Our estimate for the range of the extent of the (M/Ms =) magnetization plateau for the triangular-lattice antiferromagnet is1.37<λ<2.15, which is in good agreement with results from spin-wave theory (1.248<λ<2.145) and exactdiagonalizations (1.38<λ<2.16). Our results therefore support those from exact diagonalizationsthat indicate that the plateau begins at a higher value ofλ thanthat suggested by spin-wave theory (SWT). The CCM value for the in-plane magnetic susceptibility persite is χ = 0.065, which is below the result of SWT (evaluated to order1/S)of χSWT = 0.0794. Higher-order calculations are thus suggested for both SWT and CCMLSUBm calculations in order to determine the value ofχ for the triangular lattice conclusively.

Monte Carlo Simulation on Triple Layer Thin Film Spin Lattice in Extended Heisenberg Model

In this paper the magnetic behavior of triple layer thin film was investigated by Monte Carlo simulations. We fixed an antiferromagnetic arrangement of the lattice spins for the basal layer of the film and we studied the basal layer magnetic ordering influence on the two other layers, by calculating the out-of-plane and the in-plane magnetization, the out-of-plane and the in-plane magnetic susceptibility and the specific heat. We found out five magnetic ordering phases of the sample: ferromagnetic, antiferromagnetic, mixed phase ordering, paramagnetic and XY -like magnetic ordering of the spins, respectively.

MONTE CARLO APPROACH ON DOUBLE-LAYER MAGNETIC SPIN LATTICE IN ANISOTROPIC HEISENBERG MODEL

In this paper, we investigate the magnetic properties of double-layer thin film using Monte Carlo technique, in anisotropic Heisenberg model. The magnetization, out-of-plane and in-plane magnetic susceptibilities, and also the specific heat behaviors according to temperature are investigated in order to find out the contingent magnetic ordering phases and the critical temperatures values, for two easy-axis anisotropy parameters settings. We also calculate the relative variation rate of the critical temperature along with the easy-plane anisotropy interaction parameter distribution, and we comparatively appraise the numerical obtained results, in order to get quantitative response on the physical model parameters changes. Finally, we present a finite size effect study on magnetic susceptibility, respecting the two settings physical parameters we assumed in the paper.

Numerical Study on Magnetic Transitions in Double-Layer Spin Lattice Using Anisotropic Heisenberg Model

Monte Carlo simulations have been used to study the magnetic properties of double-layer thin film in Anisotropic Heisenberg Model with different anisotropy and direct exchange parameters, applying Metropolis algorithm. We investigate the antiferromagnetic ordering of the basal layer spins’ influence on the magnetic behavior of the superior layer. The magnetization, out-of-plane and in-plane magnetic susceptibilities, staggered magnetization and also the specific heat behaviors according to temperature are investigated in order to find out the potential magnetic ordered phases and the critical temperatures, for different parameter settings. Taking into account the balance between direct exchange and anisotropy interaction parameters we detect five different magnetic ordering states. These are: ferromagnetism, short-range ferromagnetism, antiferromagnetism, in-plane ordering and paramagnetism, which are characterized by specific properties; and we point also out some different magnetic phase transitions that can appear in the system.

DOUBLE-LAYER THIN FILMS MAGNETIC PROPERTIES DEPENDENCE ON ANISOTROPIC HEISENBERG MODEL PARAMETERS

The study of thin ferromagnetic films has become a field of great interest due to their importance for applications in magnetic-recording media, in order to create ultrahigh density magnetic data storage. Such an interest is also due to numerous specific phenomena related to the low dimension of these systems. In this paper we investigate the magnetic properties of bilayer thin film. The specific behavior of the mentioned system type is simulated using the Monte Carlo technique, in the extended anisotropic Heisenberg model. The magnetization, out-of-plane and in-plane magnetic susceptibilities behaviors according to temperature are investigated in order to find out the contingent magnetic ordering phase and the critical temperature, for two easy-axis anisotropy set parameter assignments. We have also presented the specific heat as a function of temperature for different direct exchange parameter values and we have found out a single-peak shape of the graphs, the critical point traveling to lower temperatures as the direct exchange parameter decreases, the similarity of the two presented cases being evident.