Anisotropic Magnetic Response Research Articles

Anisotropic magnetic, transport and thermodynamic properties of novel tetragonal Ce2RhGa12 compound

We report on a comprehensive study of the magnetization, resistivity and heat capacity on the single crystals of Ce2RhGa12 synthesized using Ga flux. Single crystal X-ray diffraction data confirm the tetragonal Pb/nbm structure of Ce2RhGa12, which is isostructural to Ce2PdGa12. Ce2RhGa12 orders antiferromagnetically at TN=3.5K and exhibits anisotropic magnetic behavior, inferred from the magnetization and resistivity data, taken along the two principal crystallographic directions of the crystal, viz., along [100] and [001]. The anisotropic magnetic response of Ce2RhGa12 establishes [001] as the easy axis of magnetization, and a weak meta-magnetic transition is also observed in the magnetic isotherm at 2K along the same axis. A sharp peak in specific heat signals the bulk antiferromagnetic transition at TN=3.5K, which shifts to lower temperatures in low applied fields. The electrical resistivity along the two directions shows metallic behavior from 300K down to 1.8K and establishes Ce2RhGa12 as a normal, trivalent cerium compound.

Metric-signature topological transitions in dispersive metamaterials.

The metric signature topological transitions associated with the propagation of electromagnetic waves in a dispersive metamaterial with frequency-dependent and anisotropic dielectric and magnetic responses are examined in the present work. The components of the reciprocal-space metric tensor depend upon both the electric permittivity and magnetic permeability of the metamaterial, which are taken as Drude-like dispersive models. A thorough study of the frequency dependence of the metric tensor is presented which leads to the possibility of topological transitions of the isofrequency surface determining the wave dynamics inside the medium, to a diverging photonic density of states at some range of frequencies, and to the existence of large wave vectors' modes propagating through the metamaterial.

Localization of polymer-grafted maghemite nanoparticles in a hemisphere of Janus polymer particles prepared by a self-organized precipitation (SORP) method

Microspheric Janus particles with maghemite nanoparticles (NPs) in the hemisphere were investigated. Poly(styrene) (PS)-grafted maghemite NPs were embedded into the PS phase of a PS–poly(isoprene) (PI) Janus polymer particle prepared by a Self-organized Precipitation (SORP) method. The obtained Janus particles showed magnetic field responsive drifts and rotation in water. Potential application in electric paper pixels can be expected from the anisotropic magnetic response of the particle.

Gouy phase of optical beams in anisotropic indefinite metamaterials

The Gouy phase shift of optical beams in anisotropic indefinite metamaterials displays extraordinary characteristics because of the presence of anisotropic magnetic and electric responses. We propose a simple interpretation of these characteristics from the unusual dispersion relation of the optical waves in the metamaterials, which influences the expectation value of the axial propagation constant of the focused beam.

Construction of invisibility cloaks of arbitrary shape and size using planar layers of metamaterials

Transformation optics (TO) is a powerful tool for the design of electromagnetic and optical devices with novel functionality derived from the unusual properties of the transformation media. In general, the fabrication of TO media is challenging, requiring spatially varying material properties with both anisotropic electric and magnetic responses. Though metamaterials have been proposed as a path for achieving such complex media, the required properties arising from the most general transformations remain elusive, and cannot implemented by state-of-the-art fabrication techniques. Here, we propose faceted approximations of TO media of arbitrary shape in which the volume of the TO device is divided into flat metamaterial layers. These layers can be readily implemented by standard fabrication and stacking techniques. We illustrate our approximation approach for the specific example of a two-dimensional, omnidirectional “invisibility cloak,” and quantify its performance using the total scattering cross section as a practical figure of merit.

Impedance technique for modeling electromagnetic wave propagation in anisotropic and gyrotropic media

A convenient and physically unambiguous interpretation of the invariant embedding technique is discussed in application to problems of electromagnetic wave propagation in complex media characterized by anisotropic and gyrotropic dielectric or magnetic response.

Magnetic anisotropy in thin films of Prussian blue analogues

The magnetic anisotropy of thin $(\ensuremath{\sim}200\text{ }\text{nm})$ and thick $(\ensuremath{\sim}2\text{ }\ensuremath{\mu}\text{m})$ films and of polycrystalline (diameters $\ensuremath{\sim}60\text{ }\text{nm}$) powders of the Prussian blue analogue ${\text{Rb}}_{0.7}{\text{Ni}}_{4.0}{[\text{Cr}{(\text{CN})}_{6}]}_{2.9}\ensuremath{\cdot}n{\text{H}}_{2}\text{O}$, a ferromagnetic material with ${T}_{c}\ensuremath{\sim}70\text{ }\text{K}$, have been investigated by magnetization, ESR at 50 and 116 GHz, and variable-temperature x-ray diffraction (XRD). The origin of the anisotropic magnetic response cannot be attributed to the direct influence of the solid support but the film growth protocol that preserves an organized two-dimensional film is important. In addition, the anisotropy does not arise from an anisotropic $g$ tensor nor from magnetolattice variations above and below ${T}_{c}$. By considering effects due to magnetic domains and demagnetization factors, the analysis provides reasonable descriptions of the low- and high-field data, thereby identifying the origin of the magnetic anisotropy.

Ring Current Model and Anisotropic Magnetic Response of Cyclopropane.

Three-dimensional models of the quantum mechanical current density, induced in the electron cloud of the cyclopropane molecule by a uniform magnetic field applied either along the C3 or the C2 symmetry axes (indicated by B∥ and B⊥, respectively), have been constructed via extended calculations. These models of near Hartree−Fock quality, previously shown to provide a good agreement between computed and observed values of magnetic tensors, have been used to interpret the magnitude of the diagonal components of susceptibility (χ), nuclear shielding of carbon (σC) and hydrogen (σH), and shielding at the center of mass (σCM). The source of the exceptionally large in-plane component σ⊥CM, dominating the anomalous average σavCM, is shown to be a strong delocalized current flowing around the methylene moieties and the noncyclic CH2−CH2 fragment. The total current strength for a magnetic field applied in the direction of a C2 symmetry axis is 15.7 nA/T, approximately 1.5 times larger than that calculated for B∥. T...

Magnetocrystalline anisotropy in RAu 2Ge 2 (R = La, Ce and Pr) single crystals

Anisotropic magnetic properties of single crystalline RAu 2Ge 2 (R=La, Ce and Pr) compounds are reported. LaAu 2Ge 2 exhibits a Pauli-paramagnetic behaviour whereas CeAu 2Ge 2 and PrAu 2Ge 2 show an antiferromagnetic ordering with Nèel temperatures T N = 13.5 and 9 K, respectively. The anisotropic magnetic response of Ce and Pr compounds establishes [0 0 1] as the easy axis of magnetization and a sharp spin-flip type metamagnetic transition is observed in the magnetic isotherms with H // [0 0 1]. The transport and magnetotransport behaviour of these compounds, in particular LaAu 2Ge 2, indicate an anisotropic Fermi surface. The magnetoresistivity of CeAu 2Ge 2 apparently reveals the presence of a residual Kondo interaction. A crystal electric field analysis of the anisotropic susceptibility in conjunction with the experimentally inferred Schottky heat capacity enables us to propose a crystal electric field level scheme for Ce and Pr compounds. For CeAu 2Ge 2 our values are in excellent agreement with the previous reports on neutron diffraction. The heat capacity data in LaAu 2Ge 2 show clearly the existence of Einstein contribution to the heat capacity.

Micromagnetic modeling of magnetization processes in FePt polytwin crystals

Magnetization processes in FePt polytwin crystals of L10 phase under external magnetic fields along different crystallographic directions are studied by using micromagnetic modeling. Computer simulations show highly anisotropic magnetic response of FePt polytwin crystals, and reveal strong effects of twin boundaries on magnetic domain structure evolutions. Due to high magnetocrystalline anisotropy of L10 phase, magnetic domain rotation is suppressed while magnetic domain wall motion plays a dominant role in magnetization processes. It is found that magnetostatic interaction between magnetic domains in neighboring twin crystals generates magnetic charges at the twin boundaries, which produce an internal magnetic field. The competition between the internal and external magnetic fields determines magnetic domain structures and their evolution paths, explaining the different characteristics of the magnetization curves under applied magnetic fields along different directions.

Synthesis of L1 0 Fe–Pd films by electrodeposition and thermal annealing

Fe–Pd alloy films have been prepared by electrochemical deposition from an alkaline electrolyte containing Fe sulfate, Pd chloride and 5-sulfosalicylic acid onto polycrystalline titanium substrates. The as-deposited films were nanocrystalline and magnetically soft (coercivity ∼ 25 Oe). L1 0 Fe–Pd films with a (1 1 1) preferred orientation were obtained by post-deposition thermal annealing of films with composition about 37 at% Fe in an (Ar + 5% H 2) gas flow at 500 °C. Such films exhibit hard magnetic properties, with a coercivity up to 1880 Oe, and a slightly anisotropic magnetic response, with a larger in-plane remanence. Preliminary magnetic investigations support magnetization switching through pinning of domain walls.

Gas-plasma compressional wave coupling by momentum transfer

Pressure disturbances in a gas-plasma mixed fluid will result in a hybrid response, with magnetosonic plasma waves coupled to acoustic waves in the neutral gas. In the analytical and numerical treatment presented here, we demonstrate the evolution of the total fluid medium response under a variety of conditions, with the gas-plasma linkage achieved by additional coupling terms in the momentum equations of each species. The significance of this treatment lies in the consideration of density perturbations in such fluids: there is no ‘pure’ mode response, only a collective one in which elements of the characteristics of each component are present. For example, an initially isotropic gas sound wave can trigger an anisotropic magnetic response in the plasma, with the character of each being blended in the global evolution. Hence sound waves do not remain wholly isotropic, and magnetic responses are less constrained by pure magnetoplasma dynamics.

Anisotropic magnetic response of a chiral conducting film

We use tilted magnetic fields to study the magnetoresistance of the chiral sheath of edge states that transports charge through GaAs/AlGaAs multilayers in the integer quantum Hall regime. The magnetic field component perpendicular to the layer planes ${\mathbf{B}}_{z}$ establishes the quantum Hall state, while the in-plane field ${\mathbf{B}}_{\mathrm{plane}}$ is either perpendicular or parallel to the edge-state sheath on a given mesa wall. We find orientation-dependent response of the sheath's vertical conductivity to ${\mathbf{B}}_{\mathrm{plane}},$ with lower conductivity for fields that link flux through the sheath.

Evidence for unconventional superconductivity inUPt3from magnetic torque studies

We studied the anisotropic magnetic response of the internal superconducting phases of ${\mathrm{UPt}}_{3}$ and its anisotropic magnetic susceptibility with a capacitive torque meter which is very sensitive in high fields. Experiments were performed at temperatures down to 20 mK and at various angles between the c axis (hexagonal structure) and $\stackrel{\ensuremath{\rightarrow}}{B},$ ranging from 16\ifmmode^\circ\else\textdegree\fi{} to 82\ifmmode^\circ\else\textdegree\fi{}. The samples were four single crystals grown with different methods and subjected to different annealing procedures. The normal state susceptibility has a maximum around 20 K for $\stackrel{\ensuremath{\rightarrow}}{B}$ in the $a\ensuremath{-}b$ plane which we followed up to 14 T. It may arise from hybridized uranium ion states split by the hexagonal crystal field. The magnetization curves in the superconducting (SC) regime show strong irreversibilities which are highly sample dependent. They are not correlated with the internal SC phase lines but continue up to a line of fields that lies parallel to the ${B}_{c2}$ curve and even follows its kink at the tetracritical point ${(T}^{\ensuremath{\star}}{,B}^{\ensuremath{\star}}).$ In the cleanest sample this line is shifted to fields well below the $B\ensuremath{-}C$ internal phase line which then manifests itself in a pronounced kink of the magnetization curve indicating an enhanced Ginzburg-Landau parameter $\ensuremath{\kappa}.$ In another sample the $B\ensuremath{-}C$ phase line between two of the three internal SC states could be detected even in the hysteretic region. The enhanced Ginzburg-Landau parameter $\ensuremath{\kappa}$ means a larger penetration depth and/or a shorter coherence length, clear evidence for the unconventional character of the $B\ensuremath{-}C$ phase transition. With our cleanest sample we also observe an anomalous peak effect, a region of enhanced flux pinning near ${B}_{c2},$ which is probably related to the Fulde-Ferrell-Larkin-Ovchinnikov state. In yet another sample we find a crossing of the up-down magnetization curves, also near ${B}_{c2},$ but with reversed orientation of the magnetization loops. We interpret this in terms of different flux pinning in the two main crystal directions, possibly in relation to the peak effect which is, however, masked in this sample by strong irreversibilities.

Anisotropic Magnetic Response in the Superconducting Mixed State of UPt3.

Equilibrium magnetization ${M}_{\mathrm{eq}}$ of the superconducting mixed state of UP${\mathrm{t}}_{3}$ has been measured as a function of field. At low temperatures, the discontinuity of ${\mathrm{dM}}_{\mathrm{eq}}/dH$ at the upper critical field ${H}_{c2}$ exhibits marked anisotropy between the two principal directions of the hexagonal crystal, being indiscernibly small for $H\ensuremath{\perp}c$, where the normal state paramagnetic susceptibility is largest. The results are not simply explained by the effective mass anisotropy nor by the ordinary paramagnetic effect of a spin-singlet pairing; they are rather in favor of an odd-parity pairing with an appreciable anisotropy in the pair-spin correlation.

Theory of anisotropic hybridization-broadened magnetic response in cerium and actinide systems.

Inelastic-neutron-scattering measurements on cerium and plutonium monopnictides, thought to have moderately delocalized f electrons, yield magnetic-excitation spectra with anisotropic dispersion; while reasonably sharp excitations have been observed only for USb and UTe among presumably more-delocalized uranium monopnictides and monochalcogenides. For UTe the broadening as well as the dispersion is quite anisotropic. We have now extended our previous theory for the magnetic behavior of hybridizing partially delocalized f-electron systems to include hybridization-induced relaxation effects in the magnetic response, and this work and results are reported in the present paper

Magnetic excitations of the intermediate-valence compound YbCu 2Si 2, measured on a single crystal

Neutron inelastic scattering from single crystals of YbCu 2Si 2 shows a weakly anisotropic magnetic response consisting principally of two broad humps around 3 and ≈7.5THz. While anisotropic single crystal susceptibility and Mossbauer effect data can be fitted reasonably well within an ICF picture, the model does not account very well for the observed neutron inelastic scattering whose origin may be more complex.