A stable and reproducible superconductivity transition between 80 and 93 K has been unambiguously observed both resistively and magnetically in a new Y-Ba-Cu-O compound system at ambient pressure. An estimated upper critical field H c2(0) between 80 and 180 T was obtained.

https://link.aps.org/pdf/10.1103/PhysRevLett.58.908

Superconductivity at 93 K in a new mixed-phase Y-Ba-Cu-O compound system at ambient pressure

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

/pdf/high-k-gate-dielectrics-current-status-and-materials-zjvba0c4u8.pdf

High-κ gate dielectrics: Current status and materials properties considerations

The oxide superconductors, particularly those recently discovered that are based on La2CuO4have a set of peculiarities that suggest a common, unique mechanism: they tend in every case to occur near a metal-insulator transition into an odd-electron insulator with peculiar magnetic properties. This insulating phase is proposed to be the long-sought “resonating-valence-bond” state or “quantum spin liquid” hypothesized in 1973. This insulating magnetic phase is favored by low spin, low dimensionality, and magnetic frustration. The preexisting magnetic singlet pairs of the insulating state become charged superconducting pairs when the insulator is doped sufficiently strongly. The mechanism for superconductivity is hence predominantly electronic and magnetic, although weak phonon interactions may favor the state. Many unusual properties are predicted, especially of the insulating state.

http://science.sciencemag.org/content/sci/235/4793/1196.full.pdf

The resonating valence bond state in La2CuO4 and superconductivity

A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La0.67Ca0.33MnOx. Epitaxial films that are grown on LaAIO3 substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and ∼1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.

http://science.sciencemag.org/content/sci/264/5157/413.full.pdf

Thousandfold Change in Resistivity in Magnetoresistive La-Ca-Mn-O Films

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

We describe a new class of low‐carrier‐density magnetic materials based on lanthanide‐substituted scandium and yttrium pnictides. In general, these III‐V compounds have energy gaps in the vicinty of 1 eV, and like most of the lanthanide pnictides, form in the B1 (rocksalt) structure. Substitution of rare earths for Y or Sc to form solid solutions is readily achieved. For example, we have produced GdxY1−xN by reactive magnetron cosputtering, and obtained epitaxial growth on sapphire substrates resulting in high‐quality single‐crystal thin films. These films exhibit moderately low carrier densities and high mobilities, and have interesting magnetic properties at low temperatures. In this paper we present a preliminary look at some of the properties of these materials.

Magnetic Behavior of Diluted Lanthanoid-Pnictide Systems

The upper critical field of most polycrystalline NbN thin films is anisotropic. with the perpendicular critical field H c2 ( \perp ) larger than the parallel critical field-H c2 (∥). We have measured the angular dependence H c2 (Θ) for samples with both a columnar and non-columnar microstructure. In both cases we find a rounded maximum near H c2 ( \perp ). The shape of H c2 (Θ), combined with the known microstructure of the films and the linear temperature dependence of H c2 for both field orientations leads us to conclude that the mechanism responsible for this anisotropy is an anisotropic conductivity in the film, probably due to differences in the grain boundary resistance in the plane of the film and normal to the film. In contrast, a single crystal film shows only surface superconductivity.

Microstructure, resistivity and the anisotropy of the upper critical field in NbN thin films

The magnetic flux noise generated by films and crystals of B${\mathrm{i}}_{2}$S${\mathrm{r}}_{2}$CaC${\mathrm{u}}_{2}$ ${\mathrm{O}}_{8+y}$ and YB${\mathrm{a}}_{2}$C${\mathrm{u}}_{3}$ ${\mathrm{O}}_{7\ensuremath{-}x}$, up to 30 \ensuremath{\mu}m thick and cooled in nominally zero magnetic field, has been measured at opposing surfaces by two dc superconducting quantum interference devices. For both materials, the noise sources at the two surfaces were highly correlated at specific temperatures in a given cooldown. This result suggests that the observed vortices moved as rigid rods. At other temperatures, the noise was mostly uncorrelated, suggesting that the relevant vortices were pinned at more than one point along their length.

Correlation of Vortex Motion in High- Tc Superconductors

In this paper, FeCoB amorphous thin films were deposited on glass substrates using a triode sputtering source under a uniform applied magnetic field. The as-deposited films exhibit a low coercivity of /spl sim/1.7 Oe, a high anisotropy field of /spl sim/37 Oe and 4/spl pi/M/sub s//spl sim/17.5 kG, when sputtered with a bias voltage of 180 V. The large anisotropy fields and saturations in these films result in a ferromagnetic resonance frequency as high as /spl sim/2.63 GHz, a relative permeability /spl mu/' of /spl sim/400-500 and a low dissipation /spl mu/" of 10-30 in the frequency range of 0.1-1 GHz. Upon subsequent annealing at 200-400/spl deg/C for 2 hrs, the magnetic properties of the films are found to be affected significantly. The magnetic properties of the as-deposited and the annealed films have been compared with a considering of the microstructure modification during annealing.

Effect of post-annealing on ultra-high frequency properties of amorphous FE-CO-B thin films

We have investigated the properties of NiFe2O4 thin films prepared by laser ablation of a stoichiometric NiFe2O4 target. Textured polycrystalline films were obtained on a‐SiO2 as well as on various substrates with Au, Ag, Pt, and MgF2 buffer layers. Epitaxially oriented films were obtained on MgO, (1102)‐oriented Al2O3, (1120)‐oriented Al2O3, Y‐stabilized ZrO2 (YSZ), and SrTiO3, although the crystalline quality of the films varied. Contamination by diffusion from the substrate and strains induced by both lattice constant mismatch and differential thermal expansion degraded the magnetic properties of the films, and in some cases decreased the electrical resistivity as well. By choosing the right substrate (YSZ), temperature (600 °C), and PO2 (0.01 mT), we are able to prepare epitaxial films with bulk saturation magnetization (Ms=270 G) and fairly low anisotropy (K∼105 erg/cm3) as inferred by torque magnetometry. These films and bilayers are expected to be useful in a variety of fundamental investigations...

R. B. van Dover

Papers

Magnetic Behavior of Diluted Lanthanoid-Pnictide Systems

Microstructure, resistivity and the anisotropy of the upper critical field in NbN thin films

Correlation of Vortex Motion in High- Tc Superconductors

Effect of post-annealing on ultra-high frequency properties of amorphous FE-CO-B thin films

Deposition and properties of NiFe2O4 thin films (abstract)