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We study states with spontaneous spin current, emerging in frustrated antiferromagnetic spin-$S$ chains subject to a strong external magnetic field. As a numerical tool, we use a non-Abelian symmetry realization of the density matrix renormalization group. The field dependence of the order parameter and the critical exponents are presented for zigzag chains with S=1/2, 1, 3/2, and 2.
We investigate the dependence of the electrical resistivity of $\sim 60 $nm thick single crystalline graphite samples on the defect concentration produced by proton irradiation at very low fluences. We show that the resistivity decreases few percent at room temperature after inducing defects at concentrations as low as $\sim 0.1 $ppm due to the increase in the carrier density, in agreement with theoretical estimates. The overall results indicate that the carrier densities measured in graphite are not intrinsic but related to defects and impurities.
We present a model to describe complex phases observed at mesoscopic scales in ultrathin magnetic films. The model is based on the interaction between dipolar as well as quadrupolar magnetic moments. In the special case of strong perpendicular crystal anisotropy, we show that quadrupolar degrees of freedom associated with orientation of domain walls are essential in order to correctly describe the observed phenomenology of domain formation. A nematic phase characterized by orientational order of domain walls (stripe-like) but without translational order is predicted. This isotropic-nematic transition belongs to the Kosterlitz-Thouless type in the thermodynamic limit. However, we found that in actual experimental scales, the fluctuations of the nematic order parameter are regularized by the sample size, and orientational long range order, as predicted by mean field, should be observable. The transition may be completely characterized experimentally from measurements of the magnetic structure factor as well as from the non-linear in-plane magnetic susceptibility.
The effects of pressure generated in a liquid medium, clamp, pressure cell on the in-plane and c-axis resistance, temperature-dependent Hall coefficient and low temperature, magnetoresistance in CaFe2As2 are presented. The T - P phase diagram, including the observation of a complete superconducting transition in resistivity, delineated in earlier studies is found to be highly reproducible. The Hall resistivity and low temperature magnetoresistance are sensitive to different states/phases observed in CaFe2As2. Auxiliary measurements under uniaxial, c-axis, pressure are in general agreement with the liquid medium clamp cell results with some difference in critical pressure values and pressure derivatives. The data may be viewed as supporting the potential importance of non-hydrostatic components of pressure in inducing superconductivity in CaFe2As2.
We explored the anomalously low moment in MnSi found by experiment (~0.4 $μ_{\text{B}}$/Mn) vs the moment predicted by density functional theory (~1.0 $μ_{\text{B}}$/Mn). With the addition of a Hubbard-U correction, we found several solutions with lower moments. These lower moment solutions show an unusual magnetic order and a magnetic quadrupole moment. The behavior of the moment under pressure does not follow the experimental trend.
Investigations of molecular magnets are driven both by prospective applications in future storage technology or quantum computing as well as by fundamental questions. Nowadays numerical simulation techniques and computer capabilities make it possible to investigate spin Hamiltonians with realistic arrangements of local anisotropy tensors. In this contribution I will discuss the magnetic response of a small spin system with special emphasis on non-collinear alignments of the local anisotropy axes.
We present a brief overview on some of the most significant achievements obtained by means of NMR and muSR techniques in highly frustrated magnets. First the basic quantities measured by the two techniques will be presented and their connection to the microscopic static and dynamical spin susceptibility recalled. Then the main findings will be outlined, starting from the most simple frustrated units, the molecular nanomagnets, to artificially built frustrated systems as $^{3}$He on graphite, to magnets with a macroscopically degenerate ground-state as the ones on a pyrochlore or kagomé lattices.
Single crystalline Ba(Fe(1-x)TMx)2As2 (TM = Rh, Pd) series have been grown and characterized by structural, thermodynamic and transport measurements. These measurements show that the structural/magnetic phase transitions, found in pure BaFe2As2 at 134 K, are suppressed monotonically by the doping and that superconductivity can be stablized over a dome-like region. Temperature-composition (T-x) phase diagrams based on electrical transport and magnetization measurements are constructed and compared to those of the Ba(Fe(1-x)TMx)2As2 (TM = Co, Ni) series. Despite the generic difference between 3d and 4d shells and the specific, conspicuous differences in the changes to the unit cell parameters, the effects of Rh doping are exceptionally similar to the effects of Co doping and the effects of Pd doping are exceptionally similar to the effects of Ni doping. These data show that whereas the structural / antiferromagnetic phase transition temperatures can be parameterized by x and the superconducting transition temperature can be parameterized by some combination of x and e, the number of extra electrons associated with the TM doping, the transition temperatures of 3d- and 4d- doped BaFe2As2 can not be simply parameterized by the changes in the unit cell dimensions or their ratios.
We have performed x-ray linear and circular magnetic dichroism experiments at the Mn L2,3-edge of the La0.7Sr0.3MnO3 ultra thin films. Our measurements show that the antiferromagnetic (AF) insulating phase is stabilized by the interfacial rearrangement of the Mn 3d orbitals, despite the relevant magnetostriction anisotropic effect on the double-exchange ferromagnetic (FM) metallic phase. As a consequence, the Mn atomic magnetic moment orientation and how it reacts to strain differ in the FM and AF phases. In some cases a FM insulating (FMI) phase adds to the AF and FM. Its peculiar magnetic properties include in-plane magnetic anisotropy and partial release of the orbital moment quenching. Nevertheless the FMI phase appears little coupled to the other ones.
A giant diamagnetism in the Co$_{2}$CrAl compounds, in both bulk and thin film, below a certain temperature ($T_z$) was observed. Above $T_z$, the compound behaves as an ordinary ferromagnet. The diamagnetic alignment might be initiated by the Landau diamagnetism because of the half-metallic properties and the pinning of the diamagnetism is preserved by the peculiar electronic structures.
We find the dynamical exponent $z = 3$ antiferromagnetic (AF) quantum critical point (QCP) in the heavy fermion quantum transition beyond the standard framework of the Hertz-Moriya-Millis theory with $z = 2$. Based on the U(1) slave-fermion representation of the Anderson lattice model, we show the continuous transition from an antiferromagnetic metal to a heavy fermion Fermi liquid, where the heavy fermion phase consists of two fluids, differentiated from the slave-boson theory. Thermodynamics and transport of the $z = 3$ AF QCP are shown to be consistent with the well known non-Fermi liquid physics such as the divergent Grüneisen ratio with an exponent 2/3 and temperature-linear resistivity. In particular, the uniform spin susceptibility turns out to diverge with an exponent 2/3, the hallmark of the $z = 3$ AF QCP described by deconfined bosonic spinons.
We develop a first-principles scheme based on the continued fraction approach an d ultrasoft pseudopotentials to calculate K-edge X-ray absorption spectra in solids. The method allows for calculations of K-edge X-ray absorption spectra in transition metal and rare-earths compounds with substantially reduced cutoffs respect to the norm-conserving case. We validate the method by calculating Si and O K-edges in $α$ quartz, Cu K-edge in Copper and in La$_2$CuO$_4$. For the case of Si and O edges in $α$ quartz and in Copper we obtain a good agreement with experimental data. In the Cu K-edge spectra of La$_2$CuO$_4$, a material considered a real challeng e for density functional theory we attribute all the near-edge and far-edge peaks to single particle excitations.
X-Ray diffraction, ac susceptibility and electrical resistivity measurements were performed in order to investigate the effect of Ag substitution for Pr in the polycrystalline Pr$_{1-x}$Ag$_x$MnO$_3$ (0.0$\leq$x$\leq$0.25) manganites. The XRD results show that the samples crystallize in the O'-orthorhombic structure with a cooperative Jahn-Teller deformation. We give evidence that the Ag$^{+}$ is not substituted at the Pr$^{3+}$ site in the PrMnO$_{3}$ structure. The increase of $T_{C}$ up to 130 K is suggested to be due to further oxidation of manganite grains by the oxygen released from the metallic silver at high temperatures. No metal-insulator transition was observed in the samples.
Magnetic resonant X ray scattering experiments have been performed on a single crystal of EuFe_2As_2 at the Eu L_3 absorption edge. This has permitted us to determine for the first time the orientation of Eu magnetic moments in the antiferromagnetic ordered phase below T_N=19 K as parallel to the a-axis. In addition, non-resonant magnetic X ray measurements indicate that Fe magnetic moments align along the same direction in the spin density wave phase (T<T_S~190 K). Temperature dependences indicate that the onset of the Eu AFM phase barely affects the Fe magnetic sublattice.
Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc = 0.68 K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN = 10 K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions.
The in-plane thermal conductivity $κ$ of the iron selenide superconductor FeSe$_x$ ($T_c$ = 8.8 K) were measured down to 120 mK and up to 14.5 T ($\simeq 3/4 H_{c2}$). In zero field, the residual linear term $κ_0/T$ at $ T \to 0$ is only about 16 $μ$W K$^{-2}$ cm$^{-1}$, less than 4% of its normal state value. Such a small $κ_0/T$ does not support the existence of nodes in the superconducting gap. More importantly, the field dependence of $κ_0/T$ in FeSe$_x$ is very similar to that in NbSe$_2$, a typical multi-gap s-wave superconductor. We consider our data as strong evidence for multi-gap nodeless superconductivity in FeSe$_x$. This kind of superconducting gap structure may be generic for all Fe-based superconductors.
The ground state of Fermions in a 1D trap with $δ$ function interaction is studied mathematically with group theory ideas.
More discussion from the theory is suggested