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Instruments / Technical Area	Publication Details	Published
I18-Microfocus Spectroscopy	Structure and magnetism in Cr-embedded Co nanoparticles Steve Baker , Mustafa Kurt , Mervyn Roy , Martin Lees , Chris Binns Journal Of Physics: Condensed Matter 28 DOI: 10.1088/0953-8984/28/4/046003 Diamond Proposal Number(s): [538, 12400] Show Abstract ▼ Abstract: We present the results of an investigation into the atomic structure and magnetism of 2 nm diameter Co nanoparticles embedded in an antiferromagnetic Cr matrix. The nanocomposite films used in this study were prepared by co-deposition directly from the gas phase, using a gas aggregation source for the Co nanoparticles and a molecular beam epitaxy (MBE) source for the Cr matrix material. Co K and Cr K edge extended x-ray absorption fine structure (EXAFS) experiments were performed in order to investigate atomic structure in the embedded nanoparticles and matrix respectively, while magnetism was investigated by means of a vibrating sample magnetometer. The atomic structure type of the Co nanoparticles is the same as that of the Cr matrix (bcc) although with a degree of disorder. The net Co moment per atom in the Co/Cr nanocomposite films is significantly reduced from the value for bulk Co, and decreases as the proportion of Co nanoparticles in the film is decreased; for the sample with the most dilute concentration of Co nanoparticles (4.9% by volume), the net Co moment was 0.25 μ B/atom. After field cooling to below 30 K all samples showed an exchange bias, which was largest for the most dilute sample. Both the structural and magnetic results point towards a degree of alloying at the nanoparticle/matrix interface, leading to a core/shell structure in the embedded nanoparticles consisting of an antiferromagnetic CoCr alloy shell surrounding a reduced ferromagnetic Co core.	Feb 2016
I07-Surface & interface diffraction	Silicon Σ13(5 0 1) grain boundary interface structure determined by bicrystal Bragg rod X-ray scattering P. Howes , S. Rhead , M. Roy , C. Nicklin , J. Rawle , C. Norris Acta Materialia 61 (15), 5694 - 5701 DOI: 10.1016/j.actamat.2013.06.011 Show Abstract ▼ Abstract: The atomic structure of the silicon ?13(5 0 1) symmetric tilt grain boundary interface has been determined using Bragg rod X-ray scattering. In contrast to conventional structural studies of grain boundary structure using transmission electron microscopy, this approach allows the non-destructive measurement of macroscopic samples. The interface was found to have a single structure that is fully fourfold coordinated. X-ray diffraction data were measured at Beamline I07 at the Diamond Light Source	Jul 2013
I07-Surface & interface diffraction	X-ray diffraction study of a Si & sigma 13 symmetric tilt grain boundary S. D. Rhead , P. B. Howes , M. Roy , J. L. Rawle , C. Nicklin , C. Norris Diamond Light Source Proceedings 1 SRMS 2011 DOI: 10.1017/S2044820110000523 Diamond Proposal Number(s): [2072] Show Abstract ▼ Abstract: We present an X-ray diffraction study of a semiconductor symmetric tilt grain boundary. The theory of crystal truncation rod scattering is extended to bicrystal interfaces and compared with experimental data measured at the Diamond Light Source.	Oct 2010
Detectors	Simple filters enable x-ray polarization measurements Adrian Martindale , Nigel Bannister , Daniel Cotton , George Fraser , Kenneth Harris , Benson Kariuki , Ben Palmer , Steve Collins , Greg Solan , Andrew Armitage , Mervyn Roy Spie Newsroom SPIE Newsroom DOI: 10.1117/2.1200904.1585 Show Abstract ▼ Abstract: Measurements of the degree and angle of polarization of emission from astronomical sources enable physical characterization of the objects and environmental conditions from which the photons originate. However, a lack of suitable instrumentation in the x-ray and gamma-ray regimes has been frustrating astronomers for over three decades. To date, only one unambiguous astrophysical x-ray polarization measurement has been obtained: the Crab Nebula was observed to exhibit 19% linear polarization at 2.6keV.	Apr 2009
I06-Nanoscience (XPEEM)	Loss of long-range magnetic order in a nanoparticle assembly due to random anisotropy C. Binns , P. B. Howes , S. H. Baker , P. Steadman , M. Roy , M. J. Everard , A. Rushforth , S. S. Dhesi , H. Marchetto , A. Potenza Journal Of Physics: Condensed Matter 20 (5) DOI: 10.1088/0953-8984/20/5/055213 Diamond Proposal Number(s): [051] Show Abstract ▼ Abstract: We have used soft x-ray photoemission electron microscopy (XPEEM) combined with x-ray magnetic circular dichroism (XMCD) and DC SQUID (superconducting quantum interference device) magnetometry to probe the magnetic ground state in Fe thin films produced by depositing size-selected gas-phase Fe nanoparticles with a diameter of 1.7 nm (~200 atoms) onto Si substrates. The depositions were carried out in ultrahigh vacuum conditions and thicknesses of the deposited film in the range 550 nm were studied. The magnetometry data are consistent with the film forming a correlated super-spin glass with a magnetic correlation length ~5 nm. The XPEEM magnetic maps from the cluster-assembled films were compared to those for a conventional thin Fe film with a thickness of 20 nm produced by a molecular beam epitaxy (MBE) source. Whereas a normal magnetic domain structure is observed in the conventional MBE thin film, no domain structure could be observed in any of the nanoparticle films down to the resolution limit of the XMCD based XPEEM (100 nm) confirming the ground state indicated by the magnetometry measurements. This observation is consistent with the theoretical prediction that an arbitrarily weak random anisotropy field will destroy long-range magnetic order.	Feb 2008

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