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Magnetic properties of high Tc superconductors
Vacuum/volume 39/numbers Printed in Great Britain
718lpages
859 to 864/l
0042-207X/89$3.00+.00
989
Pergamon
Press plc
Abstracts
Magnetic properties of high Z’,superconductors* A Weidinger, Hahn-Meitner-Institut, Strasse 100, 1000 Berlin 39, FRG
Bereich
P,
Glienicker
There is growing evidence that magnetic interactions play an important role in high-T, superconductivity. Experimentally, it was shown that slight changes in the stoichiometry of the highT, compounds cause a transition from superconducting to magnetically ordered phases and vice versa. Theoretically, the close relation between antiferromagnetic ordering and high-T, superconductivity was established in many papers. Recently, magnetic fluctuations were introduced explicitly as the case for the pairing of charge carriers in high-T, superconductors. In the present paper, a survey of the magnetic properties of high-T, superconductors and related compounds are presented. Special emphasis will be given to the recently discovered coexistence of magnetic correlations and superconductivity at low temperatures. Possible theoretical implications are discussed. * Invited
turbed yy-angular correlations (PAC). A first study of the electric field gradient at surfaces was performed with PAC for In (111) surfaces, where the sensitivity to growth processes has been demonstrated’. More recently, investigations of Cu surfaces have been carried out, exhibiting a clear influence of co-adsorbed Clatoms on the surface field gradient*. NMR measurements with nuclear-spin-polarized alkali-metal atoms adsorbed on W (1 IO) surfaces were reported, yielding information on averaged field gradients probed by the diffusing probe atoms’. Also MGssbauer spectroscopy has been applied to Fe (110) surfaces, for which detailed information on the surface hyperfinc fields has been gained“. In this paper our present knowledge on surface hyperfine fields, especially on electric surface field gradients, acting at metal surfaces are reviewed. It is shown that the electric surface field gradient can serve as a fingerprint for the detection of probe sites at surfaces and diffusion phenomena. Acknowledgement This work gemeinschaft,
is supported by Bonn (SFB 306).
the
Dcutsche
Forschungs-
References Electron and ion emission from individual atoms* Hans-Werner Fink, IBM Research Division, Laboratory, 8803 Riischlikon, Switzerland
Ziirich
Research
By using field ion techniques it has been possible to create atomic arrangements that emit electrons or ions from a region in space confined to an individual atom or a small cluster made up of no more than six atoms. These ultra-sharp tips constitute point sources for electrons or noble gas ions. The properties of the resulting ensemble of particles will be presented in view of their density, angular spread and energy distribution. The ability to image surfaces by means of a low-energy (1.5 eV) electron beam as well as prospective applications that accompany the small size (e.g. coherence) of the source will also be discussed. * Invited.
‘Surface studies with hyperfine probes* G Schatz, Universitiit Konstanz,
7750 Konstanz,
FRG
The interest in the study of microscopic phenomena at surfaces via electromagnetic hyperfine fields has increased rapidly during I he last few years. The efforts in this research area have been concentrated on applications of hyperfine techniques like nuclear magnetic resonance (NMR), Mtissbauer spectroscopy and per-
’ W KGrner, W Keppner, B Lehndorff-Junges and G Schatz, Phys Reo Let?, 49, 1735 (1982). 2T Klas, J Voigt, W Keppner, R Wesche and G Schatz, Phys Reo Lett, 57, 1068 (1986). 3 B Horn, E Koch and D Fick, Phys Ret Lerr, 53, 364 (1984). a J Korecki and U Gradmann, Phys Ret: Left, 55, 249 I (I 9X5) ; Europhys Left, 2, 651 (1986). * Invited.
Applications of high spatial resolution XPS C M Demanet, VG ScientiJic Limited, The Birches Industrial Estate, Imberhorne Lane, East Grinstead, West Sussex, RH19 1 UB, UK XPS has the advantage over the commonly-used technique for surface analysis of being non-destructive and providing chemical information. It is also particularly suited to the study of many of the new materials which, like most composite materials, are insulators. However, until recently it suffered from relatively poor spatial resolution (limited at best to 150 Atm). A recent break through in XPS instrumentation allows the 150 pm barrier to be broken and provides high spatial resolution XPS analysis. Examples of applications of high spatial resolution XPS on technologically important materials are given to illustrate the power of the technique.
859
718lpages
859 to 864/l
0042-207X/89$3.00+.00
989
Pergamon
Press plc
Abstracts
Magnetic properties of high Z’,superconductors* A Weidinger, Hahn-Meitner-Institut, Strasse 100, 1000 Berlin 39, FRG
Bereich
P,
Glienicker
There is growing evidence that magnetic interactions play an important role in high-T, superconductivity. Experimentally, it was shown that slight changes in the stoichiometry of the highT, compounds cause a transition from superconducting to magnetically ordered phases and vice versa. Theoretically, the close relation between antiferromagnetic ordering and high-T, superconductivity was established in many papers. Recently, magnetic fluctuations were introduced explicitly as the case for the pairing of charge carriers in high-T, superconductors. In the present paper, a survey of the magnetic properties of high-T, superconductors and related compounds are presented. Special emphasis will be given to the recently discovered coexistence of magnetic correlations and superconductivity at low temperatures. Possible theoretical implications are discussed. * Invited
turbed yy-angular correlations (PAC). A first study of the electric field gradient at surfaces was performed with PAC for In (111) surfaces, where the sensitivity to growth processes has been demonstrated’. More recently, investigations of Cu surfaces have been carried out, exhibiting a clear influence of co-adsorbed Clatoms on the surface field gradient*. NMR measurements with nuclear-spin-polarized alkali-metal atoms adsorbed on W (1 IO) surfaces were reported, yielding information on averaged field gradients probed by the diffusing probe atoms’. Also MGssbauer spectroscopy has been applied to Fe (110) surfaces, for which detailed information on the surface hyperfinc fields has been gained“. In this paper our present knowledge on surface hyperfine fields, especially on electric surface field gradients, acting at metal surfaces are reviewed. It is shown that the electric surface field gradient can serve as a fingerprint for the detection of probe sites at surfaces and diffusion phenomena. Acknowledgement This work gemeinschaft,
is supported by Bonn (SFB 306).
the
Dcutsche
Forschungs-
References Electron and ion emission from individual atoms* Hans-Werner Fink, IBM Research Division, Laboratory, 8803 Riischlikon, Switzerland
Ziirich
Research
By using field ion techniques it has been possible to create atomic arrangements that emit electrons or ions from a region in space confined to an individual atom or a small cluster made up of no more than six atoms. These ultra-sharp tips constitute point sources for electrons or noble gas ions. The properties of the resulting ensemble of particles will be presented in view of their density, angular spread and energy distribution. The ability to image surfaces by means of a low-energy (1.5 eV) electron beam as well as prospective applications that accompany the small size (e.g. coherence) of the source will also be discussed. * Invited.
‘Surface studies with hyperfine probes* G Schatz, Universitiit Konstanz,
7750 Konstanz,
FRG
The interest in the study of microscopic phenomena at surfaces via electromagnetic hyperfine fields has increased rapidly during I he last few years. The efforts in this research area have been concentrated on applications of hyperfine techniques like nuclear magnetic resonance (NMR), Mtissbauer spectroscopy and per-
’ W KGrner, W Keppner, B Lehndorff-Junges and G Schatz, Phys Reo Let?, 49, 1735 (1982). 2T Klas, J Voigt, W Keppner, R Wesche and G Schatz, Phys Reo Lett, 57, 1068 (1986). 3 B Horn, E Koch and D Fick, Phys Ret Lerr, 53, 364 (1984). a J Korecki and U Gradmann, Phys Ret: Left, 55, 249 I (I 9X5) ; Europhys Left, 2, 651 (1986). * Invited.
Applications of high spatial resolution XPS C M Demanet, VG ScientiJic Limited, The Birches Industrial Estate, Imberhorne Lane, East Grinstead, West Sussex, RH19 1 UB, UK XPS has the advantage over the commonly-used technique for surface analysis of being non-destructive and providing chemical information. It is also particularly suited to the study of many of the new materials which, like most composite materials, are insulators. However, until recently it suffered from relatively poor spatial resolution (limited at best to 150 Atm). A recent break through in XPS instrumentation allows the 150 pm barrier to be broken and provides high spatial resolution XPS analysis. Examples of applications of high spatial resolution XPS on technologically important materials are given to illustrate the power of the technique.
859