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Instruments / Technical Area	Publication Details	Published	Actions
I06-Nanoscience	Exchange-bias via nanosegregation in novel Fe 2–x Mn 1+x Al ( x = –0.25, 0, 0.25) Heusler films Samer Kurdi , Massimo Ghidini , Giorgio Divitini , Bhaskaran Nair , Ahmed Kursumovic , Paola Tiberto , Sarnjeet Dhesi , Zoe Barber Nanoscale Advances DOI: 10.1039/C9NA00689C Diamond Proposal Number(s): [17563] Open Access Show Abstract ▼ Abstract: Exchange-bias has been reported in bulk nanocrystalline Fe2MnAl, but individual thin films of this Heusler alloy have never been studied so far. Here we study the structural and magnetic properties of nanocrystalline thin films of Fe2–xMn1+xAl (x = –0.25, 0, 0.25) obtained by sputtering and ex-situ post-deposition annealing. We find that Fe2MnAl films display exchange-bias, and that varying Mn concentration determines the magnitude of the effect, which can be either enhanced (in Fe1.75Mn1.25Al) or suppressed (in Fe2.25Mn0.75Al). X-ray diffraction (XRD) shows that our films present a mixed L21-B2 Heusler structure where increasing Mn concentration favors the partial transformation of the L21 phase into the B2 phase. Scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX) reveal that this composition-driven L21→B2 transformation is accompanied by phase segregation at the nanoscale. As a result, the Fe2–xMn1+xAl films that show exchange-bias (x = 0, 0.25) are heterogeneous, with nanograins of an Fe-rich phase embedded in a Mn-rich matrix (a non-negative matrix factorisation algorithm was used to give an indication of the phase composition from EDX data). Our comparative analysis of XRD, magnetometry and X-ray magnetic circular dichroism (XMCD), shows that Fe-rich nanograins and Mn-rich matrix are composed of a ferromagnetic L21 phase and an antiferromagnetic B2 phase, respectively, thus revealing that exchange-coupling between these two phases is the cause of the exchange-bias effect. Our work should inspire the development of single-layer, environmentally-friendly spin valve devices based on nanocomposite Heusler films.	May 2020
I20-Scanning-X-ray spectroscopy (XAS/XES)	Extracting structural information of Au colloids at ultra-dilute concentrations: identification of growth during nanoparticle immobilization George F. Tierney , Donato Decarolis , Norli Abdullah , Scott M. Rogers , Shusaku Hayama , Martha Briceno De Gutierrez , Alberto Villa , C. Richard A. Catlow , Paul Collier , Nikolaos Dimitratos , Peter Wells Nanoscale Advances 4 DOI: 10.1039/C9NA00159J Diamond Proposal Number(s): [17283] Open Access Show Abstract ▼ Abstract: Sol-immobilization is increasingly used to achieve supported metal nanoparticles (NPs) with controllable size and shape; it affords a high degree of control of the metal particle size and yields a narrow particle size distribution. Using state-of-the-art beamlines, we demonstrate how X-ray absorption fine structure (XAFS) techniques are now able to provide accurate structural information on nano-sized colloidal Au solutions at μM concentrations. This study demonstrates: (i) the size of Au colloids can be accurately tuned by adjusting the temperature of reduction, (ii) Au concentration, from 50 μM to 1000 μM, has little influence on the average size of colloidal Au NPs in solution and (iii) the immobilization step is responsible for significant growth in Au particle size, which is further exacerbated at increased Au concentrations. The work presented demonstrates that an increased understanding of the primary steps in sol-immobilization allows improved optimization of materials for catalytic applications.	May 2019

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