Magnetic and crystalline microstructure of nanocrystalline metals studied by neutron and synchrotron radiation scattering

Radosław Przeniosło 2Rolf Hempelmann 1Izabela Sosnowska 2

1. University of Saarbruecken, Institute of Physical Chemistry, Saarbrücken 66123, Germany
2. Warsaw University, Institute of Experimental Physics (IEP UW), Hoża 69, Warszawa 00-681, Poland

Abstract



The crystalline and magnetic microstruture of nanocrystalline Ni (n-Ni), Co (n-Co) and Cr (n-Cr) have been studied by means of X-ray and neutron diffraction as well as small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS). The nanocrystalline samples obtained by electrodeposition have crystallite sizes between 10 nm and 60 nm and relative densities of the order of 95%. SANS and SAXS studies show that the crystalline microstructure has fractal-like density correlations with coherence lengths exceeding the limitations o the SAS techniques, i.e. above 100 nm. The magnetic ordering of n-Ni and n-Co at RT is made of ferromagnetic domains with sizes exceeding a single crystallite. The magnetic ordering of n-Cr and polycrystalline Cr (poly-Cr) has been studied with powder neutron diffraction at temperatures between 2 K and 300 K. The magnetic ordering of n-Cr is antiferromagnetic between RT and 240 K. At 240 K the magnetic ordering changes and a part of the material adopts a transverse spin density wave (TSDW) ordering. The spin-flip transition from the TSDW to the longitudinal LDSW ordering is supressed and about 40 % of the volume has the TSDW ordering stabilized down to 2 K. The thermal lattice expansion of the material becomes negative around the magnetic phase transition near 240 K. The values of the magnetic moments of the simple antiferromagnetic and TSDW orderings observed at 2K are in agreement with the magnetic moments observed in single crystals and poly-Cr.

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Presentation: invited oral at E-MRS Fall Meeting 2003, Symposium B, by Radosław Przeniosło
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-06-11 15:16
Revised:   2009-06-08 12:55
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