Electrical resistivity rho, magnetic susceptibility chi, magnetization M and specific heat measurements are reported on a singlecrystalline sample of CePd5Al2, showing successive antiferromagnetic orderings at T_N1=4.1 K and T_N2=2.9 K. The temperature dependence of T_N1 shows a Kondo metal behavior with large anisotropy, rho_c/rho_a=3.2 at 20 K, and opening of a superzone gap along the tetragona c-direction below T_N1. Both T_N1 and T_N2 gradually increase with applying pressure up to 2.5 GPa. The data of chi(T) and M(B) in the paramagnetic state were analyzed using a crystalline electric field (CEF) model. It led to a Kramers doublet ground state with wave functions consisting primarily of |+-5/2>, whose energy level is isolated from the excited states by 230 and 300 K. This CEF effect gives rise to the large anisotropy in the paramagnetic state. In the ordered state, the uniaxial magnetic anisotropy is manifested as M_c/M_a=20 in B=5 T and at 1.9 K, and chi_c/chi_a=25 in B=0.1 T and at 4 K. This huge uniaxial magnetic anisotropy in the antiferromagnetic states can be interpreted in terms of isotropic magnetic interaction among the Ce^{3+} moments governed by the strong CEF. In powder neutron diffraction experiments, magnetic reflections were observed owing to the antiferromagnetic ordered states below T_N1, however, no additional reflection was found below T_N2.
La0.67Sr0.33MnO3 (LSMO) thin films under compressive strain have an orthorhombic symmetry with (1-10)o and (001)o in-plane orientations. (The subscript o denotes the orthorhombic symmetry.) Here, we grew LSMO on cubic (LaAlO3)0.3-(Sr2AlTaO6)0.7 (LSAT) substrates and observed a uniaxial contribution to the magnetic anisotropy which is related to the orthorhombic crystal structure. Since the lattice mismatch is equal in the two directions, the general understanding of anisotropy in LSMO, which relates the uniaxial anisotropy to differences in strain, cannot explain the results. These findings su…
The Mn2BO4 single crystals have been grown using the flux technique. The careful study crystal structure and magnetic properties have been carried out. The antiferromagnet transition at TN = 26 K has been traced through the dc magnetization and specific heat temperature dependences. The magnetic uniaxial anisotropy has been detected with easy axis of magnetization lying in ab-plane. A reduction of the effective magnetic moment value is assigned to the non-quenched orbital moment of Jahn-Teller Mn3+ ions. Based on the superexchange interactions calculations the magnetic behavior is discussed.
We investigate ground-state properties of a one-dimensional S=1 spin-orbital model with or without uniaxial single-ion anisotropy. By means of the density matrix renormalization group method, we compute the ground-state energy, the magnetization curves and the correlation functions. We discuss how the ground-state properties depend on the two exchange couplings for orbital and spin sectors. The phase diagram obtained is compared with that for the S=1/2 model. We also address the effect of uniaxial single-ion anisotropy.
We use inelastic neutron scattering to study the temperature and energy dependence of the spin excitation anisotropy in uniaxial-strained electron-doped iron pnictide BaFe$_{1.9}$Ni$_{0.1}$As$_2$ near optimal superconductivity ($T_c=20$ K). Our work has been motivated by the observation of in-plane resistivity anisotropy in the paramagnetic tetragonal phase of electron-underdoped iron pnictides under uniaxial pressure, which has been attributed to a spin-driven Ising-nematic state or orbital ordering. Here we show that the spin excitation anisotropy, a signature of the spin-driven Ising-nemati…
We provide evidence of an intermediate Haldane phase in a spin-2 quantum chain. By combining effective field theory and numerical approaches, we show that the phase diagram of the proposed model includes SO(5) Haldane, intermediate Haldane, and large-D phases. We determine the characteristic properties of these phases, including edge states, string order parameters, and degeneracies in the entanglement spectrum. The symmetries responsible for the degeneracy patterns observed in the entanglement spectrum are also discussed.
${\rm CaRuO_3}$ is a paramagnetic metal and since its low temperature resistivity is described by $ρ=ρ_0+AT^γ$ with $γ\sim 1.5$, it is also considered a non-Fermi liquid (NFL) metal. We have performed extensive magnetoresistance and Hall effect measurements of untwinned epitaxial films of ${\rm CaRuO_3}$. These measurements reveal that ${\rm CaRuO_3}$ exhibits uniaxial magnetocrystalline anisotropy. In addition, the low-temperature NFL behavior is most effectively suppressed when a magnetic field is applied along the easy axis, suggesting that critical spin fluctuations, possibly due to proxim…
Classical ground state of the isotropic Heisenberg spin Hamiltonian on a primitive Bravais lattice is known to be a single-Q planar spin spiral. A uniaxial anisotropy and external magnetic field distort this structure by generating the higher-order Fourier harmonics at wave-vectors nQ in the spatial spin configuration. These features are not captured in the formalism based on the Luttinger-Tisza theorem, where the classical ground state energy is minimized under the ``weak'' condition on the length of the spins. We discuss why the correct solution is lost in that approach and present an altern…
We present a detailed study on the magnetic properties, including anisotropy, reversal fields, and magnetization reversal processes, of well characterized half-metallic epitaxial La0.7Sr0.3MnO3 (LSMO) thin films grown onto SrTiO3 (STO) substrates with three different surface orientations, i.e. (001), (110) and (1-18). The latter shows step edges oriented parallel to the [110] (in-plane) crystallographic direction. Room temperature high resolution vectorial Kerr magnetometry measurements have been performed at different applied magnetic field directions in the whole angular range. In general, t…
The spin dynamics of the semiclassical Heisenberg model with uniaxial anisotropy, on the layered triangular lattice with antiferromagnetic coupling for both intralayer nearest neighbor interaction and interlayer interaction is studied both in the ordered phase and in the paramagnetic phase, using the Monte Carlo-molecular dynamics technique. The important quantities calculated are the full dynamic structure function $S(\bf q, ω)$, the chiral dynamic structure function $S_{chi}(ω)$, the static order parameter and some thermodynamic quantities. Our results show the existence of propagating modes…
Ground-state phase diagrams and magnetization curves of a spin-1 Heisenberg diamond cluster with two different coupling constants and uniaxial single-ion anisotropy are investigated in a presence of the external magnetic field with the help of exact diagonalization methods. It is shown that the spin-1 Heisenberg diamond cluster exhibits several remarkable quantum ground states, which are manifested in zero- and low-temperature magnetization curves as intermediate plateaus at one-quarter, one-half and three-quarters of the saturation magnetization. It is found that the width of the fractional m…
We study the effects of transverse magnetic fields on the $S=1$ one-dimensional Kondo lattice model with a uniaxial anisotropy using the density matrix renormalization group. The model can be regarded as a simplified one for analyzing the Ising ferromagnetic superconductor URhGe. We find various phases such as ferromagnetic and antiferromagnetic phases, Kondo plateau (KP) phases, Tomonaga-Luttinger liquids, and fully polarized phases. In the KP phase, a pseudoplateau emerges in the magnetization due to strongly bound pairs between the local and the conduction electron spins. This is why we cal…
One dimensional S=1 XXZ chains with uniaxial single-ion-type anisotropy are studied by numerical exact diagonalization of finite size systems. The numerical data are analyzed using conformal field theory, the level spectroscopy, phenomenological renormalization group and finite size scaling method. We thus present the first quantitatively reliable ground state phase diagram of this model. The ground states of this model contain the Haldane phase, large-D phase, Néel phase, two XY phases and the ferromagnetic phase. There are four different types of transitions between these phases: the Brezins…
Magnetic skyrmions, vortex-like topological spin textures, have attracted much interest in a wide range of research fields from fundamental physics to spintronics applications. Recently, growing attention has also been paid to antiskyrmions emerging in opposite topological charge in non-centrosymmetric magnets with $D_{2\mathrm{d}}$ or $S_4$ symmetry. In these magnets, complex interplay among anisotropic Dzyaloshinskii-Moriya interaction, uniaxial magnetic anisotropy, and magnetic dipolar interactions generates a variety of magnetic structures. However, the relation between the stability of an…
The thermodynamic properties of S>=1 ferromagnetic chains with an easy-axis single-ion anisotropy are investigated at arbitrary temperatures by both a Green-function approach, based on a decoupling of three-spin operator products, and by exact diagonalizations of chains with up to N=12 sites using periodic boundary conditions. A good agreement between the results of both approaches is found. For the S=1 chain, the temperature dependence of the specific heat reveals two maxima, if the ratio of the anisotropy energy D and the exchange energy J exceeds a characteristic value, D/J >7.4, and only o…
Ca3Co2O6 is a system exhibiting a series of fascinating properties, including magnetization plateaus and remarkably slow dynamics at low-T. These properties are intimately related to the geometrical frustration, which results from a particular combination of features: (i) the chains are arranged on a triangular lattice; (ii) there is a large uniaxial anisotropy; (iii) the intrachain and interchain couplings are ferromagnetic and antiferromagnetic, respectively. The uniaxial anisotropy is thus an issue of crucial importance for the analysis of the physical properties of Ca3Co2O6. However, it tu…
The influence of uniaxial single-ion anisotropy -DSz^2 on the magnetic and thermal properties of Heisenberg antiferromagnets (AFMs) is investigated. The uniaxial anisotropy is treated exactly and the Heisenberg interactions are treated within unified molecular field theory (MFT) [Phys. Rev. B 91, 064427 (1915)], where thermodynamic variables are expressed in terms of directly measurable parameters. The properties of collinear AFMs with ordering along the z axis (D > 0) in applied fields Hz = 0 are calculated versus D and temperature T. The high-field average magnetization per spin muz(Hz,D,T) …
We explore the field induced magnetic phases of an $S=1$ $XXZ$ model with single-ion anisotropy and large Ising-like anisotropy on a Shastry Sutherland lattice over a wide range of Hamiltonian parameters and applied magnetic field. The multitude of ground state phases are characterized in detail in terms of their thermodynamic properties and the underlying classical (Ising limit) spin arrangements for the plateau phases are identified by calculating the static structure factors. The enlarged local Hilbert space of the $S=1$ spins results in several new ground state phases that are not realized…
We report giant anisotropy in thermoelectric power factor ($S^2σ$) of marcasite structure-type PtSb$_{1.4}$Sn$_{0.6}$. PtSb$_{1.4}$Sn$_{0.6}$, synthesized using ambient pressure flux growth method upon mixing Sb and Sn on the same atomic site, is a new phase different from both PtSb$_2$ and PtSn$_2$ that crystallize in the cubic $Pa\bar{3}$ pyrite and $Fm\bar{3}m$ fluorite unit cell symmetry, respectively. Giant difference in $S^2σ$ for heat flow applied along different principal directions of the orthorhombic unit cell mostly stems from anisotropic Seebeck coefficients.
Surface magnetic domains of a UCoGa single crystal during magnetization/demagnetization processes in increasing/decreasing magnetic fields were investigated by means of magnetic-force-microscopy (MFM) images at low temperatures. The observed domain structure is typical for a ferromagnet with strong uniaxial anisotropy. The evolution of magnetic domains during cooling of the crystal below TC has also been manifested by MFM images. Analysis of the available data reveals that the high uniaxial magnetocrystalline energy in combination with the relatively small ferromagnetic exchange interaction in…
Crossover and Changeover in Spin-1 Kitaev-$Γ$ Chain with Uniaxial Single-ion Anisotropy
Nanjing University of Aeronautics and Astronautics（南京航空航天大学）；Beijing Computational Science Research Center（北京计算科学研究中心）；Nankai University（南开大学）；Beijing University of Posts and Telecommunications（北京邮电大学）；Lanzhou University（兰州大学）；Zhejiang University（浙江大学）
Uniaxial phase of the axial quadrupole spin-1 magnet in an external magnetic field is investigated. A case where the system includes single-ion anisotropy and anisotropic biquadratic exchange interaction the most general form, is considered. It is proved, that the molecular field approximation of the relative magnetization does not depend on temperature and increases linearly with the external magnetic field. Two branches of the spin excitation spectrum are derived. Condition of mitigation of the spectrum defines the boundary between the axial quadrupole and angular phases. The critical temper…
The quantum Fisher information is of considerable interest not only for quantum metrology but also because it is a useful entanglement measure for finite temperature mixed states. In particular, it estimates the degree to which multipartite entanglement is present. Recent results have related the quantum Fisher information to experimentally measurable probes. While in principle possible, a direct evaluation of the quantum Fisher information at finite temperatures is technically challenging and here we show that a simple estimate can be obtained for materials where the single mode approximation…
When Heisenberg spins interact antiferromagnetically on a triangular lattice and nearest-neighbor interactions dominate, the ground state is 120$^{\circ}$ antiferromagnetism. In this work, we probe the response of this state to lifting the triangular symmetry, through investigation of the triangular antiferromagnet PdCrO$_2$ under uniaxial stress by neutron diffraction and resistivity measurements. The periodicity of the magnetic order is found to change rapidly with applied stress; the rate of change indicates that the magnetic anisotropy is roughly forty times the stress-induced bond length …
Anisotropic electron-phonon interaction is shown to lead to the anisotropic polaron effect. The resulting anisotropy of the polaron band is an exponential function of the electron-phonon coupling and might be as big as $10^3$. This also makes anisotropy very sensitive to small changes of coupling and implies wide variations of anisotropy among compounds of similar structure. The isotope effect on mass anisotropy is predicted. Polaron masses are obtained by an exact Quantum Monte Carlo method. Implications for high-temperature superconductors are briefly discussed.
The phase diagram of the XXZ spin-1 quantum magnet on the kagome lattice is studied for all cases where the $J_z$ coupling is antiferromagnetic. In the zero magnetic field case, the six previously introduced phases, found using various methods, are: the nondegenerate gapped photon phase which breaks no space symmetry or spin symmetry; the six-fold degenerate phase with plaquette order, which breaks both time reversal symmetry and translational symmetry; the "superfluid" (ferromagnetic) phase with an in-plane global U(1) symmetry broken, when $J_{xy} < 0$; the $\sqrt{3}\times\sqrt{3}$ order whe…
We have performed nuclear quadrupole resonance and nuclear magnetic resonance measurements on UCoAl with strong Ising-type anisotropy under $b$- and $c$-axes uniaxial pressure. In the $b$-axis uniaxial pressure ($P_{\parallel b}$) measurement, we observed an increase in the metamagnetic transition field with increasing $P_{\parallel b}$. In the $c$-axis uniaxial pressure ($P_{\parallel c}$) measurement, on the other hand, we observed a ferromagnetic transition in zero magnetic field along the $c$-axis above $P_{\parallel c}$ = 0.08 GPa. The anomaly of the nuclear spin-lattice relaxation rate d…
The transport properties of a large-spin molecule strongly coupled to ferromagnetic leads in the presence of transverse magnetic anisotropy are studied theoretically. The relevant spectral functions, linear-response conductance and the tunnel magnetoresistance are calculated by means of the numerical renormalization group method. We study the dependence of transport characteristics on orbital level position, uniaxial and transverse anisotropies, external magnetic field and temperature. It is shown that while uniaxial magnetic anisotropy leads to the suppression of the Kondo effect, finite tran…
We study uniaxially strained graphene under the influence of non-uniform magnetic fields perpendicular to the material sample with a coordinate independent strain tensor. For that purpose, we solve the Dirac equation with anisotropic Fermi velocity and explore the conditions upon which such an equation possesses a supersymmetric structure in the quantum mechanical sense through examples. Working in a Laudau-like gauge, wave functions and energy eigenvalues are found analytically in terms of the magnetic field intensity, the anisotropy scales and other relevant parameters that shape the magneti…
Resistivity measurements were carried out up to 8 GPa on single crystal and polycrystalline samples of CeCu2Si2 from differing sources in the homogeneity range. The anisotropic response to current direction and small uniaxial stresses was explored, taking advantage of the quasi-hydrostatic environment of the Bridgman anvil cell. It was found that both the superconducting transition temperature Tc and the normal state properties are very sensitive to uniaxial stress, which leads to a shift of the valence instability pressure Pv and a small but significant change in Tc for different orientations…
We employed small-angle neutron scattering to demonstrate that the magnetic skyrmion lattice can be realized in bulk chiral magnets as a thermodynamically stable state at temperatures much lower than the ordering temperature of the material. This is in the regime where temperature fluctuations become completely irrelevant to the formation of the topologically non-trivial magnetic texture. In this attempt we focused on the model helimagnet MnSi, in which the skyrmion lattice was previously well characterized and shown to exist only in a very narrow phase pocket close to the Curie temperature of…
We theoretically propose that giant magnetochiral anisotropy is achieved in Weyl semimetals in noncentrosymmetric crystals as a consequence of the chiral anomaly. The magnetochiral anisotropy is the nonlinearity of the resistivity $ρ$ that depends on the current $\boldsymbol{I}$ and the magnetic field $\boldsymbol{B}$ as $ρ=ρ_0 (1 + γ\boldsymbol{I} \cdot \boldsymbol{B})$, and can be applied to rectifier devices controlled by $\boldsymbol{B}$. We derive the formula for the coefficient $γ$ in noncentrosymmetric Weyl semimetals. The obtained formula for $γ$ shows that the magnetochiral anisotropy…
We have studied anisotropic magnetoresistance (MR) and magnetization with rotating magnetic field (B) within $CuO_2$ plane in lightly doped AF $Nd_{2-x}Ce_xCuO_{4}$. \emph{A giant anisotropy} in MR is observed at low temperature below 5 K. The c-axis resistivity can be tuned about one order of magnitude just by changing B direction within $CuO_2$ plane and a scaling behavior between out-of-plane and in-plane MR is found. A "Spin valve" effect is proposed to understand the giant anisotropy of out-of-plane MR and the evolution of scaling parameters with the external field. It is found that the f…
