The last decade witnessed significant progress in angle-resolved photoemission spectroscopy (ARPES) and its applications. Today, ARPES experiments with 2-meV energy resolution and $0.2\ifmmode^\circ\else\textdegree\fi{}$ angular resolution are a reality even for photoemission on solids. These technological advances and the improved sample quality have enabled ARPES to emerge as a leading tool in the investigation of the high-${T}_{c}$ superconductors. This paper reviews the most recent ARPES results on the cuprate superconductors and their insulating parent and sister compounds, with the purpose of providing an updated summary of the extensive literature. The low-energy excitations are discussed with emphasis on some of the most relevant issues, such as the Fermi surface and remnant Fermi surface, the superconducting gap, the pseudogap and $d$-wave-like dispersion, evidence of electronic inhomogeneity and nanoscale phase separation, the emergence of coherent quasiparticles through the superconducting transition, and many-body effects in the one-particle spectral function due to the interaction of the charge with magnetic and/or lattice degrees of freedom. Given the dynamic nature of the field, we chose to focus mainly on reviewing the experimental data, as on the experimental side a general consensus has been reached, whereas interpretations and related theoretical models can vary significantly. The first part of the paper introduces photoemission spectroscopy in the context of strongly interacting systems, along with an update on the state-of-the-art instrumentation. The second part provides an overview of the scientific issues relevant to the investigation of the low-energy electronic structure by ARPES. The rest of the paper is devoted to the experimental results from the cuprates, and the discussion is organized along conceptual lines: normal-state electronic structure, interlayer interaction, superconducting gap, coherent superconducting peak, pseudogap, electron self-energy, and collective modes. Within each topic, ARPES data from the various copper oxides are presented.

https://arxiv.org/pdf/cond-mat/0208504.pdf

Angle-resolved photoemission studies of the cuprate superconductors

We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on the common structural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVI alloys in the absence of an external magnetic field, stressing the close relationship of the sp electron bands in these materials to the band structure of the nonmagnetic AIIBVI ‘‘parent’’ semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half‐filled Mn 3d5 shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of the magnetic properties of the AII1−xMnxBVI alloys. In particular, we discuss the mechanism of the Mn++‐Mn++ exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susc...

Diluted magnetic semiconductors

A new compound composed of Nd, Fe, and a small quantity of B (about 1 wt. %) has been found, which has a tetragonal structure with lattice constants a=0.880 nm and c=1.221 nm. This phase, which has the approximate composition, 12 at. % Nd, 6 at. % B and balance Fe, possesses remarkable magnetic properties. From the approach to saturation an anisotroy constant of about 3.5 MJ/m3 can be calculated, while saturation magnetization amounts to 1.35 T. The magnetization versus temperature curve shows a Curie temperature of 585 K, which is much higher than those of the Fe and light rare earth binary compounds. Based on the new compound, sintered permanent magnets have been developed which have a record high energy product. Permanent magnet properties and physical properties of a typical specimen which has the composition Nd15B8Fe77 are as follows: Br =1.23 T, HcB =880 kA/m, HcI =960 kA/m, (BH)max =290 kJ/m3, temperature coefficient of Br =−1260 ppm/K, density=7.4 Mg/m3, specific resistivity=1.4 μΩm, Vickers hardn...

New material for permanent magnets on a base of Nd and Fe (invited)

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

Exchange anisotropy — a review

A microscopic explanation of exchange bias in thin films with compensated ferro/antiferromagnetic interfaces is presented. Full micromagnetic calculations show the interfacial exchange coupling to be relatively strong with a perpendicular orientation between the ferro/antiferromagnetic axis directions, similar to the classic ``spin-flop'' state in bulk antiferromagnets. With reasonable parameters the calculations predict bias fields comparable to those observed and provide a possible explanation for both anomalous high field rotational hysteresis and recently discovered ``positive'' exchange bias.

Calculations of Exchange Bias in Thin Films with Ferromagnetic/Antiferromagnetic Interfaces

Conversion-electron M\"ossbauer measurements have been used to study hyperfine fields in Fe/Ag(100) single-crystal multilayer films at temperatures down to 15 K. The Fe layer thicknesses corresponded to 1.0, 2.4, and 5.5 monolayers (ML). From the relative intensity of the M\"ossbauer lines we show conclusively that the orientation of the magnetic moment of the 1.0- and 2.4-ML films in zero applied field is perpendicular to the film plane while the orientation of the 5.5-ML sample is in plane at room temperature and partially out of plane at low temperatures. The low-temperature hyperfine fields are enhanced compared to bulk Fe.

Direct evidence for perpendicular spin orientations and enhanced hyperfine fields in ultrathin Fe(100) films on Ag(100).

Magnetization data are presented on sputter-deposited amorphous $R {\mathrm{Fe}}_{2}$ materials, where $R$ represents the rare-earth elements Tb, Gd, and Y. Both the Tb and Gd compounds exhibit ferrimagnetic order with Curie temperatures approximately 40% lower than the equivalent crystalline Laves phase compounds. The 0 K saturation magnetizations of the Gd amorphous and crystalline materials are both equal to 3.9${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, while in the Tb${\mathrm{Fe}}_{2}$ the magnetization is significantly lower in the amorphous phase (4.2${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ vs 5.4${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ for crystalline Tb${\mathrm{Fe}}_{2}$). The Y${\mathrm{Fe}}_{2}$ exhibits no long-range magnetic order above 3.5 K. At low temperatures large "coercive" fields appear for the Tb${\mathrm{Fe}}_{2}$ and increase greatly in magnitude at temperatures below 40 K, reaching 30 kG at 4 K. A possible model to explain this and other effects associated with a large random-directional local anisotropy field is presented.

Anomalous magnetization of amorphous Tb Fe 2 , Gd Fe 2 , and Y Fe 2

Using x-ray-absorption fine-structure measurements we have obtained clear evidence for structural anisotropy in amorphous sputter-deposited TbFe films exhibiting perpendicular magnetic anisotropy. Modeling of the data shows that perpendicular anisotropy in these films is associated with Fe-Fe and Tb-Tb pair correlations which are greater in plane and Tb-Fe correlations which are greater perpendicular to the film plane. Upon annealing at 300 \ifmmode^\circ\else\textdegree\fi{}C the measured structural anisotropy disappears and the magnetic anisotropy decreases to a level consistent with magnetoelastic interactions between the film and substrate.

N. C. Koon

Papers

Calculations of Exchange Bias in Thin Films with Ferromagnetic/Antiferromagnetic Interfaces

Direct evidence for perpendicular spin orientations and enhanced hyperfine fields in ultrathin Fe(100) films on Ag(100).

Anomalous magnetization of amorphous Tb Fe 2 , Gd Fe 2 , and Y Fe 2

Structural origins of magnetic anisotropy in sputtered amorphous Tb-Fe films

Giant magnetostriction materials