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Magnetic impurity

About: Magnetic impurity is a research topic. Over the lifetime, 3711 publications have been published within this topic receiving 70047 citations.


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TL;DR: It is proposed thatferromagnetic exchange here, and in dilute ferromagnetic nitrides, is mediated by shallow donor electrons that form bound magnetic polarons, which overlap to create a spin-split impurity band.
Abstract: Dilute ferromagnetic oxides having Curie temperatures far in excess of 300 K and exceptionally large ordered moments per transition-metal cation challenge our understanding of magnetism in solids. These materials are high-k dielectrics with degenerate or thermally activated n-type semiconductivity. Conventional super-exchange or double-exchange interactions cannot produce long-range magnetic order at concentrations of magnetic cations of a few percent. We propose that ferromagnetic exchange here, and in dilute ferromagnetic nitrides, is mediated by shallow donor electrons that form bound magnetic polarons, which overlap to create a spin-split impurity band. The Curie temperature in the mean-field approximation varies as (xdelta)(1/2) where x and delta are the concentrations of magnetic cations and donors, respectively. High Curie temperatures arise only when empty minority-spin or majority-spin d states lie at the Fermi level in the impurity band. The magnetic phase diagram includes regions of semiconducting and metallic ferromagnetism, cluster paramagnetism, spin glass and canted antiferromagnetism.

2,743 citations

Journal ArticleDOI
TL;DR: In this article, a linear specific heat at low temperatures for glass follows naturally from general considerations on the glassy state, and the experimentally observed anomalous low-temperature thermal conductivity is predicted.
Abstract: We show that a linear specific heat at low temperatures for glass follows naturally from general considerations on the glassy state. From the same considerations we obtain the experimentally observed anomalous low-temperature thermal conductivity, and we predict an ultrasonic attenuation which increases at low temperatures. Possible relationships with the linear specific heat in magnetic impurity systems are pointed out. We suggest experimental study of the relaxation of thermal and other properties.

2,578 citations

Journal ArticleDOI
TL;DR: In this article, the theory of impurity conduction was introduced and the following conclusions were drawn: 1) impurity can be inferred from impurity, and 2) impur-ture conduction can be predicted.
Abstract: (1961). The theory of impurity conduction. Advances in Physics: Vol. 10, No. 38, pp. 107-163.

1,170 citations

Journal ArticleDOI
TL;DR: In this article, the authors provide a unified framework for describing quasi-localized states in the vicinity of impurity sites in conventional and unconventional superconductors and show that these fluctuations affect the density of states and are, strictly speaking, gapless in the presence of an arbitrarily small concentration of magnetic impurities.
Abstract: We review recent developments in our understanding of how impurities influence the electronic states in the bulk of superconductors. Our focus is on the quasi-localized states in the vicinity of impurity sites in conventional and unconventional superconductors and our goal is to provide a unified framework for their description. The non-magnetic impurity resonances in unconventional superconductors are directly related to the Yu-Shiba-Rusinov states around magnetic impurities in conventional s-wave systems. We review the physics behind these states, including quantum phase transition between screened and unscreened impurity, and emphasize recent work on d-wave superconductors. The bound states are most spectacularly seen in scanning tunneling spectroscopy measurements on high-$T_c$ cuprates, which we describe in detail. We also discuss very recent progress on the states coupled to impurity sites which have their own dynamics, and impurity resonances in the presence of an order competing with superconductivity. Last part of the review is devoted to influence of local deviations of the impurity concentration from its average value on the density of states in s-wave superconductors. We review how these fluctuations affect the density of states and show that s-wave superconductors are, strictly speaking, gapless in the presence of an arbitrarily small concentration of magnetic impurities.

968 citations

Journal ArticleDOI
TL;DR: In this paper, the polarization of graphene is calculated exactly within the random phase approximation for arbitrary frequency, wavevector and doping, and the dynamical polarization for low q and arbitrary ω is employed to calculate the dispersion relation and the decay rate of plasmons and acoustic phonons.
Abstract: The polarization of graphene is calculated exactly within the random phase approximation for arbitrary frequency, wavevector and doping. At finite doping, the static susceptibility saturates to a constant value for low momenta. At q = 2kF it has a discontinuity only in the second derivative. In the presence of a charged impurity this results in Friedel oscillations which decay with the same power law as the Thomas–Fermi contribution, the latter being always dominant. The spin density oscillations in the presence of a magnetic impurity are also calculated. The dynamical polarization for low q and arbitrary ω is employed to calculate the dispersion relation and the decay rate of plasmons and acoustic phonons as a function of doping. The low screening of graphene, combined with the absence of a gap, leads to a significant stiffening of the longitudinal acoustic lattice vibrations.

953 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20236
202225
202152
202044
201957
201869