This review summarizes recent developments in the theory of spin glasses, as well as pertinent experimental data. The most characteristic properties of spin glass systems are described, and related phenomena in other glassy systems (dielectric and orientational glasses) are mentioned. The Edwards-Anderson model of spin glasses and its treatment within the replica method and mean-field theory are outlined, and concepts such as "frustration," "broken replica symmetry," "broken ergodicity," etc., are discussed. The dynamic approach to describing the spin glass transition is emphasized. Monte Carlo simulations of spin glasses and the insight gained by them are described. Other topics discussed include site-disorder models, phenomenological theories for the frozen phase and its excitations, phase diagrams in which spin glass order and ferromagnetism or antiferromagnetism compete, the Ne\'el model of superparamagnetism and related approaches, and possible connections between spin glasses and other topics in the theory of disordered condensed-matter systems.

Spin glasses: Experimental facts, theoretical concepts, and open questions

Amorphous alloys were first developed over 40 years ago and found applications as magnetic core or reinforcement added to other materials. The scope of applications is limited due to the small thickness in the region of only tens of microns. The research effort in the past two decades, mainly pioneered by a Japanese- and a US-group of scientists, has substantially relaxed this size constrain. Some bulk metallic glasses can have tensile strength up to 3000 MPa with good corrosion resistance, reasonable toughness, low internal friction and good processability. Bulk metallic glasses are now being used in consumer electronic industries, sporting goods industries, etc. In this paper, the authors reviewed the recent development of new alloy systems of bulk metallic glasses. The properties and processing technologies relevant to the industrial applications of these alloys are also discussed here. The behaviors of bulk metallic glasses under extreme conditions such as high pressure and low temperature are especially addressed in this review. In order that the scope of applications can be broadened, the understanding of the glass-forming criteria is important for the design of new alloy systems and also the processing techniques.

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Shek-MaterSciEng04-Bulk%20Metallic%20Glasses.pdf

Bulk metallic glasses

The elastic properties, elastic models and elastic perspectives of metallic glasses

Although the vast majority of high-$T_c$ cuprate superconductors are hole-doped, a small family of electron-doped compounds exists. Under investigated until recently, there has been tremendous recent progress in their characterization. A consistent view is being reached on a number of formerly contentious issues, such as their order parameter symmetry, phase diagram, and normal state electronic structure. Many other aspects have been revealed exhibiting both their similarities and differences with the hole-doped compounds. This review summarizes the current experimental status of these materials, with a goal to providing a snapshot of our current understanding of electron-doped cuprates. When possible we put our results in the context of the hole-doped compounds. We attempt to synthesize this information into a consistent view on a number of topics important to both this material class as well as the overall cuprate phenomenology including the phase diagram, the superconducting order parameter symmetry, phase separation, pseudogap effects, the role of competing orders, the spin-density wave mean-field description of the normal state, and electron-phonon coupling.

Progress and perspectives on electron-doped cuprates

In 1897 Guillaume1 discovered that face-centred cubic alloys of iron and nickel with a nickel concentration of around 35 atomic per cent exhibit anomalously low (almost zero) thermal expansion over a wide temperature range. This effect, known as the Invar effect, has since been found in various ordered and random alloys and even in amorphous materials2. Other physical properties of Invar systems, such as atomic volume, elastic modulus, heat capacity, magnetization and Curie (or Neel) temperature, also show anomalous behaviour. Invar alloys are used in instrumentation, for example as hair springs in watches. It has long been realized that the effect is related to magnetism2,3; but a full understanding is still lacking. Here we present ab initio calculations of the volume dependences of magnetic and thermodynamic properties for the most typical Invar system, a random face-centred cubic iron–nickel alloy, in which we allow for non-collinear spin alignments—that is, spins that may be canted with respect to the average magnetization direction. We find that the magnetic structure is characterized, even at zero temperature, by a continuous transition from the ferromagnetic state at high volumes to a disordered non-collinear configuration at low volumes. There is an additional, comparable contribution to the net magnetization from the changes in the amplitudes of the local magnetic moments. The non-collinearity gives rise to an anomalous volume dependence of the binding energy, and explains other peculiarities of Invar systems.

Origin of the Invar effect in iron–nickel alloys

We report magnetic susceptibility, electrical resistivity, and Hall-effect measurements on single crystals from the $n$-type high- ${T}_{c}$ superconducting system ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4\ensuremath{-}\ensuremath{\delta}}$. Using an improved reduction technique, we find that bulk superconductivity can be established over the broad Ce concentration range $0.04\ensuremath{\le}x\ensuremath{\le}0.17$. The new superconducting phase diagram and the systematics of the electronic transport properties resemble those observed in the overdoped concentration range of the $p$-type high- ${T}_{c}$ superconductors.

Extended Superconducting Concentration Range Observed in Pr 2-x Ce x CuO 4-δ

The bulk moduli of rocksalt-type divalent and trivalent rare-earth ($R$) monochalcogenides exhibit a linear relationship when plotted on a log-log scale against the unit-cell volume, but fall on two distinct straight lines according to the effective valence product of the compound. By comparing the bulk modulus ratio of the $R$ monochalcogenide to the alkali halide at the same volume, we have estimated the effective ionic charges. These charges are found to be 1.7\ifmmode\pm\else\textpm\fi{}0.03 and 1.85\ifmmode\pm\else\textpm\fi{}0.05 for the ${R}^{2+}$ and ${R}^{3+}$ compounds, respectively, as against 2 and 2.45 expected from their valence products. The behavior of NaCl-type Ce monopnictides is somewhat anomalous.

Effective ionic charge and bulk modulus scaling in rocksalt-structured rare-earth compounds

We report magnetic and electric measurements on $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ with up to 15 at.% substitution of Ni, Fe, and Zn for Cu in the insulating state ($\ensuremath{\delta}\ensuremath{\simeq}1$) and the metallic state ($\ensuremath{\delta}\ensuremath{\simeq}0.1$). The concentration dependence of the Pauli susceptibility and the electrical conductivity indicates that the shift of the Fermi energy towards the mobility edge with increasing degree of substitution is one important mechanism for the suppression of the superconducting transition temperature. In the insulating antiferromagnetic state the Fe and Ni spins are very weakly coupled to the Cu spins. The Ni spins remain paramagnetic down to the lowest measuring temperature of 3 K, the Fe spins order at 5 K, independent of the Fe concentration. The N\'eel temperature depends weakly on the Fe and Zn concentration but decreases strongly with the Ni concentration. This different behavior reflects the different site preference for the substitution in the insulating state, namely Cu(2) for Ni and Cu(1) for Fe and Zn.

Influence of Ni, Fe, and Zn substitution on the superconducting and antiferromagnetic state of YBa2Cu3O7- delta.

Superconductivity in Bi2Sr2CaCu2O8+ delta single crystals doped with Fe, Ni, and Zn.

/pdf/acoustic-mode-vibrational-anharmonicity-related-to-the-19150ylc8j.pdf

H. Bach

Papers

Extended Superconducting Concentration Range Observed in Pr 2-x Ce x CuO 4-δ

Effective ionic charge and bulk modulus scaling in rocksalt-structured rare-earth compounds

Influence of Ni, Fe, and Zn substitution on the superconducting and antiferromagnetic state of YBa2Cu3O7- delta.

Superconductivity in Bi2Sr2CaCu2O8+ delta single crystals doped with Fe, Ni, and Zn.

Acoustic-mode vibrational anharmonicity related to the anomalous thermal expansion of Invar iron alloys.