The intermetallic compound U${\mathrm{Ru}}_{2}$${\mathrm{Si}}_{2}$ can be classified as a heavy-fermion system because of its large linear specific-heat coefficient $\ensuremath{\gamma}=180$ mJ/mol\ifmmode\cdot\else\textperiodcentered\fi{}${\mathrm{K}}^{2}$. Susceptibility, magnetization, and measurements on single-crystal samples indicate both magnetic phase transition at 17.5 K superconducting 0.8 K. properties are highly anisotropic.

Scanning tunneling spectroscopy was used to investigate single crystals and thin films of La(1-x)Ca(x)MnO(3) (with x about 0.3), which exhibit colossal magnetoresistance. The different spectroscopic signatures the insulating (paramagnetic) metallic (ferromagnetic) phases enable their spatial extent be imaged down a lateral scale order 10 nanometers. Above bulk transition temperature T(c), images show mostly behavior. Below phase separation is observed where inhomogeneous structures more...

The theory for thermally assisted flux flow (TAFF) in the limit of small driving forces is used to derive exact expressions time-dependent behaviour magnetisation and permeability. problem especially relevant high-temperature superconductors where large variations transition temperature DC fields are observed as a function frequency probing AC field. parameters extensively discussed relation present understanding pinning.

Neutron scattering demonstrates the coexistence of antiferromagnetic order and superconductivity below 1 K in heavy-electron system ${\mathrm{URu}}_{2}$${\mathrm{Si}}_{2}$. It is found that upper (17.5 K) transition to an phase with a (100) modulation wave vector spins along tetragonal c-axis. The ordered moment unusually small, (0.03\ifmmode\pm\else\textpm\fi{}0.01)${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$. However, spin waves develop from damped, finite-gap excitations above...

This Colloquium reviews the 25 year quest to understand continuous (second-order), mean-field-like phase transition occurring at 17.5 K in ${\mathrm{URu}}_{2}{\mathrm{Si}}_{2}$. About ten years ago, term ``hidden order'' (HO) was coined and has since been utilized describe unknown ordered state, whose origin cannot be disclosed by conventional solid-state probes, such as x rays, neutrons, or muons. The HO is able support superconductivity lower temperatures...

Antiferromagnetic order and fluctuations in the heavy-fermion superconductor ${\mathrm{URu}}_{2}$${\mathrm{Si}}_{2}$ have been studied by magnetic neutron scattering. Below ${\mathit{T}}_{\mathit{N}}$=17.5 K, is a type-I antiferromagnet with an anomalously small ordered moment of (0.04\ifmmode\pm\else\textpm\fi{}0.01)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ polarized along tetragonal c axis. Dispersive resonant excitations exist state zone-center gap 0.43 THz. The are large dipolar matrix...

The complex ac susceptibility of the two-dimensional Ising spin glass ${\mathrm{Rb}}_{2}$${\mathrm{Cu}}_{0.782}$${\mathrm{Co}}_{0.218}$${\mathrm{F}}_{4}$ is measured as a function temperature and frequency. results are first analyzed in terms Cole-Cole formalism. It found that median relaxation time ${\ensuremath{\tau}}_{c}$ diverges towards ${T}_{c}$=0 K over many 16 decades according to activated dynamics, i.e.,...

We present low-temperature volume thermal expansion, beta, and specific heat, C, measurements on high-quality single crystals of CeNi2Ge2 YbRh2(Si0.95Ge0.05)(2) which are located very near to quantum critical points. For both systems, beta shows a more singular temperature dependence than thus the Grüneisen ratio Gamma proportional beta/C diverges as T-->0. CeNi2Ge2, our results in accordance with spin-density wave (SDW) scenario for three-dimensional spin fluctuations. By contrast, observed...

Electrical-resistivity measurements \ensuremath{\rho}(T,H) on single-crystal ${\mathrm{URu}}_{2}$${\mathrm{Si}}_{2}$ have been performed between 0.3 and 300 K in fields up to 7 T. \ensuremath{\rho}(T) is highly anisotropic with the 300-K values parallel a c axes differing by factor of 2. Both directions exhibit d\ensuremath{\rho}/dT<0 down 80 K, followed steep decrease \ensuremath{\rho} below 50 K. An upper antiferromagnetic transition clearly discerned ``Cr-like'' anomaly at...

Heavy electronic states originating from the f atomic orbitals underlie a rich variety of quantum phases matter. We use scale imaging and spectroscopy with scanning tunneling microscope to examine novel that emerge uranium in URu(2)Si(2). find that, as temperature is lowered, partial screening electrons' spins gives rise spatially modulated Kondo-Fano resonance maximal between surface U atoms. At T = 17.5 K, URu(2)Si(2) known undergo second-order phase transition Kondo lattice state into...

Zero-field muon-spin-resonance and lower-critical-field data are presented for a wide range of Th concentrations in ${\mathrm{U}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Th}}_{\mathit{x}}$${\mathrm{Be}}_{13}$, spanning the region where both superconducting second, lower-temperature phase transition observed. Overall T-x boundaries assigned discussed according to nature lower transition. Arguments associating with possible magnetic (time-reversal--violating) state given.

Uncovering the symmetry of a hidden order Cooling matter generally makes it more ordered and may induce dramatic transitions: Think water becoming ice. With increased comes loss symmetry; in its liquid form will look same however you rotate it, whereas ice not. Kung et al. studied properties mysteriously phase material URu 2 Si that appears at 17.5 K. They shone laser light on crystal shifts frequency light. The electron orbitals uranium had handedness to them alternated between atomic...

We have performed elastic neutron-scattering experiments on the heavy-electron compound URu_2Si_2 for pressure P up to 2.8 GPa. found that antiferrmagnetic (100) Bragg reflection below T_m ~ 17.5 K is strongly enhanced by applying pressure. For < 1.1 GPa, staggered moment mu_o at 1.4 increases linearly from 0.017(3) mu_B 0.25(2) mu_B, while slightly a rate 1 K/GPa, roughly following transition temperature T_o determined macroscopic anomalies. also observed sharp phase P_c 1.5 above which...

URh_2Ge_2 occupies an extraordinary position among the heavy-electron 122-compounds, by exhibiting a previously unidentified form of magnetic correlations at low temperatures, instead usual antiferromagnetism. Here we present new results ac and dc susceptibilities, specific heat neutron diffraction on single-crystalline as-grown URh_2Ge_2. These data clearly indicate that crystallographic disorder local scale produces spin glass behavior in sample. We therefore conclude is 3D Ising-like,...

We report the magnetic susceptibility, specific heat and dielectric constant for high-purity polycrystalline samples of three hexagonal manganites: YMnO3, LuMnO3 ScMnO3. These materials can exhibit a ferroelectric transition at very high temperatures (TFE>700 K). At lower there is ordering frustrated Mn3+ spins (S = 2) on triangular Mn lattice (YMnO3: TN 71 K; LuMnO3: 90 K ScMnO3: 130 The characterized by sharp kink in susceptibility below which it continues to increase due frustration...

The low-temperature phase of the dilute Ising antiferromagnet ${\mathrm{Fe}}_{0.55}$${\mathrm{Mg}}_{0.45}$${\mathrm{Cl}}_{2}$ in zero field is studied by specific-heat, ac-susceptibility, and neutron-scattering experiments. We find that this phase, spin-glass behavior antiferromagnetic long-range order coexist. Such a mixed-order predicted mean-field theory reentrant spin-glasses, but has never been observed before.

New measurements of the ac susceptibility in zero field for a (${\mathrm{Eu}}_{0.2}$${\mathrm{Sr}}_{0.8}$)S single crystal are reported. For first time spin-glass we can resolve frequency dependence inphase component ${\ensuremath{\chi}}^{\ensuremath{'}}$ (dispersion) as well out-of-phase ${\ensuremath{\chi}}^{\ensuremath{'}\ensuremath{'}}$ (absorption). From these studies clear change dynamic behavior system around freezing temperature is found, which be related to large ferromagnetic...

We have measured the ac susceptibility for $\mathrm{Au}\mathrm{Mn}$ containing 2.98 at.% Mn. Below spin-glass freezing temperature ${T}_{f}$ a small frequency dependence of $\ensuremath{\chi}$ is found. The application an external magnetic field near shows distinct reduction ${\ensuremath{\chi}}^{\ensuremath{'}}$. A comparison behavior with that other metallic alloys manganese made.

We report a comprehensive electronic structure investigation of the paramagnetic (PM), large moment antiferromagnetic (LMAF), and hidden order (HO) phases URu$_2$Si$_2$. have performed relativistic full-potential calculations on basis density functional theory (DFT), employing different exchange-correlation functionals to treat electron correlations within open $5f$-shell uranium. Specifically, we investigate---through comparison between calculated low-temperature experimental...

Over the past few years two new descriptive terms have entered lexicon of magnetism: spin glass and mictomagnet. Both these apply to non‐dilute magnetic alloys where there is a random freezing impurity moments at distinct temperature which gives rise sharp peak in low field susceptibility sudden splitting Mössbauer spectrum, along with remanence, irreversibility relaxation. Spin refers mainly lower concentration regime long range indirect RKKY interaction responsbile for cooperative spins....