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Instruments / Technical Area	Publication Details	Published
I06-Nanoscience	Robust ferromagnetism of chromium nanoparticles formed in superfluid helium Shengfu Yang , Cheng Feng , Daniel Spence , Aula M. A. A. Al Hindawi , Elspeth Latimer , Andrew M. Ellis , Chris Binns , Davide Peddis , Sarnjeet S. Dhesi , Liying Zhang , Yafei Zhang , Kalliopi N. Trohidou , Marianna Vasilakaki , Nikolaos Ntallis , Ian Maclaren , Frank M. F. De Groot Advanced Materials DOI: 10.1002/adma.201604277 Diamond Proposal Number(s): [11485] Open Access Show Abstract ▼ Abstract: Chromium nanoparticles are formed using superfluid helium droplets as the nanoreactors, which are strongly ferromagnetic. The transition from antiferromagentism to ferromagnetism is attributed to atomic scale disorder in chromium nanoparticles, leading to abundant unbalanced surface spins. Theoretical modeling confirms a frustrated aggregation process in superfluid helium due to the antiferromagnetic nature of chromium.	Oct 2016
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
I06-Nanoscience	Exchange bias in Fe@Cr core-shell nanoparticles Chris Binns , Muhammad Qureshi , Davide Peddis , Steve Baker , Paul Howes , Adrian Boatwright , Stuart Cavill , Sarnjeet S. Dhesi , Leonardo Lari , Roland Kröger , Sean Langridge Nano Letters 13 (7), 3334 - 3339 DOI: 10.1021/nl401587t Show Abstract ▼ Abstract: We have used X-ray magnetic circular dichroism and magnetometry to study isolated Fe@Cr core–shell nanoparticles with an Fe core diameter of 2.7 nm (850 atoms) and a Cr shell thickness varying between 1 and 2 monolayers. The addition of Cr shells significantly reduces the spin moment but does not change the orbital moment. At least two Cr atomic layers are required to stabilize a ferromagnetic/antiferromagnetic interface and generate the associated exchange bias and increase in coercivity.	Jun 2013
I18-Microfocus Spectroscopy	Probing atomic structure in magnetic core/shell nanoparticles using synchrotron radiation S. H. Baker , M. Roy , S. C. Thornton , M. Qureshi , C. Binns Journal Of Physics: Condensed Matter 22 (38) DOI: 10.1088/0953-8984/22/38/385301 Show Abstract ▼ Abstract: Core/shell Fe/Cu and Fe/Au nanoparticles were prepared directly by deposition from the gas phase. A detailed study of the atomic structure in both the cores and shells of the nanoparticles was undertaken by means of extended absorption fine structure (EXAFS) measurements. For Fe/Cu nanoparticles, a Cu shell ∼20 monolayers thick appears similar in structure to bulk Cu and is sufficient to cause the structure in the Fe core to switch from body centred cubic (bcc; as in bulk Fe) to face centred cubic. This is not the case for thinner Cu shells, 12 monolayers in thickness, in which there is a considerable contraction in nearest-neighbour interatomic distance as the shell structure changes to bcc. In Fe/Au nanoparticles, the crystal structure in the Fe core remains bcc for all Au thicknesses although there is some stretching of the lattice. In thin Au shells ∼2 monolayers thick, there is strong contraction in interatomic distances. There does not appear to be significant alloying at the Fe/Au interface.	Sep 2010
I06-Nanoscience	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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