J. E. Crow

Bio: J. E. Crow is an academic researcher from Temple University. The author has contributed to research in topics: Kondo effect & Magnetic susceptibility. The author has an hindex of 15, co-authored 63 publications receiving 1037 citations.

Magnetic order of Pr in PrBa2Cu3O7.

Abstract: The magnetic order of Pr in nonsuperconducting PrBa{sub 2}Cu{sub 3}O{sub 7} has been studied by specific-heat, susceptibility, and neutron-diffraction measurements. The basic ordering consists of a simple antiferromagnetic arrangement, with a saturated moment of 0.24{mu}{sub {ital B}} and a Neel temperature {ital T}{sub {ital N}} of {similar to}17 K, which is two orders of magnitude higher than expected from either dipolar or Rudeman-Kittel-Kasuya-Yosida interactions alone. The small moment, along with the large value of the low-temperature electronic specific-heat coefficient {gamma} of 196 mJ/mol K{sup 2}, suggests that there is substantial {ital f}-electron character at the Fermi level.

Resistive behavior and intermediate valence effects in La1−xCexPd3 and CePd3−xRhx

Abstract: The electrical resistivity of CePd3, La1−xCexPd3, CeRhxPd3−x and Ce Pd3+x systems has been measured from helium temperature to 300 K. The resistivity of pure CePd3 rises from 125 μ Ω cm to 150 μ Ω cm as one cools from 300 K to 100 K. Below 100 K the resisitivity drops dramatically to 10 μ Ω cm at low temperatures. The same qualitative behavior, though less pronounced, is observed in other systems such as CeSn3 which like CePd3 are believed to be of intermediate valence. For x<0.3 the system La1−xCexPd3 is believed to be trivalent. We observe Kondo‐like behavior in this regime. For x near unity we observe that extremely small amounts of La eliminate the rapid fall in resistivity observed below 100 K for pure CePd3. These results suggest that this fall off is due to some type of cooperative Ce ion hehavior. The CeRhxPd3−x system allows one to monitor the effect on resistivity of varying the Ce valence from 3.45 in CePd3 to 4 in CeRh.64Pd2.36. We find that the magnitude of the resistivity rise (upon cooling from 300 K to low temperature) decreases as the Ce valence increases towards four.

Observation of magnetic-field-induced superconductivity in a heavy-fermion antiferromagnet: CePb3.

Abstract: We report here an entirely new phenomenon, namely magnetic-field-induced superconductivity in Ce${\mathrm{Pb}}_{3}$, a system which at zero field is a heavy-fermion antiferromagnet. This phenomenon is novel in several respects. It is the first reported heavy-fermion magnetic-field-induced superconductor. It is also the first reported magnetic-field-induced superconductor that is also an antiferromagnet. Moreover, it has the simplest crystal structure, ${\mathrm{Cu}}_{3}$Au, of any known heavy-fermion or magnetic-field-induced superconductor.

Interaction of H 2 O with a high-temperature superconductor

Abstract: The effect of water on the high-temperature superconductor YBa/sub 2/Cu/sub 3/O/sub 7/ has been studied. Photoemission measurements show that water modifies valence-band states, reduces the number of inequivalent Ba sites and induces O 1s corelevel components at 534 and 531 eV. The 534-eV core-level component is coincident with that of cryosorbed ice and the enhanced 531-eV component is due to a new water-induced bonding environment in the superconductor;this is most probably a hydroxyl species. Changes in the Ba core-level appearance suggest that water may be preferentially modifying YBa/sub 2/CuO/sub 7/ in a way that affects the Ba atomic environment. The effect of water on superconductivity and its possible implications for bulk superconducting transport in ceramics is discussed. Previous reports suggesting oxygen dimerization below T/sub c/, as well as other reported changes in the spectrum, are improbable in view of these present results

Exact results in the theory of magnetic alloys

Abstract: Recently it has been shown that many traditional models used for a description of dilute magnetic alloys are completely integrable and may be solved exactly without any approximation. In this article we summarize the results which have been obtained in this way. The main part of the article is devoted to the consistent and detailed account of the Bethe-Ansatz technique for the s-d exchange (Kondo) model with arbitrary impurity spin, s-d model with anisotropic exchange, degenerate exchange model and for the canonical Anderson model. The thermodynamic properties of a magnetic impurity in a non-magnetic metal host obtained by the Bethe method are considered in detail. Mainly attention is paid to the analysis of singularities associated with the formation of a localized moment, Kondo effect and mixedvalence phenomenon, which can be treated analytically. In the introductory part of the article we discuss the applicability of the models which we study in the paper to the real alloys and consider some m...

Valence fluctuation phenomena

Abstract: Valence fluctuation phenomena occur in rare-earth compounds in which the proximity of the 4f level to the Fermi energy leads to instabilities of the charge configuration (valence) and/or of the magnetic moment. The authors review the experimental results observed in the subset of such systems for which the 4f ions form a lattice with identical valence on each site. The discussion includes key thermodynamic experiments, such as susceptibility and lattice constant, and spectroscopic experiments such as XPS and neutron scattering. This is followed by a review of existing theoretical work concerning both the ground states and the isomorphic phase transitions which occur in such compounds; the emphasis is on those aspects which make valence fluctuation phenomena such a challenging many-body problem.

Magnetism in ultrathin film structures

Abstract: In this paper, we review some of the key concepts in ultrathin film magnetism which underpin nanomagnetism. We survey the results of recent experimental and theoretical studies of well characterized epitaxial structures based on Fe, Co and Ni to illustrate how intrinsic fundamental properties such as the magnetic exchange interactions, magnetic moment and magnetic anisotropies change markedly in ultrathin films as compared with their bulk counterparts, and to emphasize the role of atomic scale structure, strain and crystallinity in determining the magnetic properties. After introducing the key length scales in magnetism, we describe the 2D magnetic phase transition and survey studies of the thickness dependent Curie temperature and the critical exponents which characterize the paramagnetic–ferromagnetic phase transition. We next discuss recent experimental and theoretical results on the determination of the exchange constant, followed by an overview of measurements of the magnetic moment in the elemental 3d transition metal thin films in the various crystal phases that have been successfully stabilized, thereby illustrating the sensitivity of the magnetic moment to the local symmetry and to the atomic environment. Finally, we discuss briefly the magnetic anisotropies of Fe, Co and Ni in the fcc crystalline phase, to emphasize the role of structure and the details of the interface in influencing the magnetic properties. The dramatic effect that adsorbates can have on the magnetic anisotropies of thin magnetic films is also discussed. Our survey demonstrates that the fundamental properties, namely, the magnetic moment and magnetic anisotropies of ultrathin films have dramatically different behaviour compared with those of the bulk while the comparable size of the structural and magnetic contributions to the total energy of ultrathin structures results in an exquisitely sensitive dependence of the magnetic properties on the film structure.