Browsing by Author "Cottrell, SP"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Complex magnetic properties associated with competing local and itinerant magnetism in Pr2Co0.86Si2.88
    (Springer Nature, 2021-06-24) Kundu, M; Pakhira, S; Choudhary, R; Paudyal, D; Lakshminarasimhan, N; Avdeev, M; Cottrell, SP; Adroja, DT; Ranganathan, R; Mazumdar, C
    Ternary intermetallic compound Pr2Co0.86Si2.88 has been synthesized in single phase and characterized by x-ray diffraction, scanning electron microscopy with energy dispersive x-ray spectroscopy (SEM-EDX) analysis, magnetization, heat capacity, neutron diffraction and muon spin rotation/relaxation (μSR) measurements. The polycrystalline compound was synthesized in single phase by introducing necessary vacancies in Co/Si sites. Magnetic, heat capacity, and zero-field neutron diffraction studies reveal that the system undergoes magnetic transition below ∼4 K. Neutron diffraction measurement further reveals that the magnetic ordering is antiferromagnetic in nature with an weak ordered moment. The high temperature magnetic phase has been attributed to glassy in nature consisting of ferromagnetic clusters of itinerant (3d) Co moments as evident by the development of internal field in zero-field μSR below 50 K. The density-functional theory (DFT) calculations suggest that the low temperature magnetic transition is associated with antiferromagnetic coupling between Pr 4f and Co 3d spins. Pr moments show spin fluctuation along with unconventional orbital moment quenching due to crystal field. The evolution of the symmetry and the crystalline electric field environment of Pr-ions are also studied and compared theoretically between the elemental Pr and when it is coupled with other elements such as Co. The localized moment of Pr 4f and itinerant moment of Co 3d compete with each other below ∼20 K resulting in an unusual temperature dependence of magnetic coercivity in the system. This article is licensed under a Creative Commons Attribution 4.0 International License.
  • Thumbnail Image
    Item
    Interaction of the Mu-cyclohexadienyl radical with metallic (Au, Pt) nanoparticles in mesoporous silica
    (IOP Publishing, 2014-12-16) Xiao, J; Arseneau, DJ; Bridges, MD; Cortie, DL; Cottrell, SP; Dehn, M; Fleming, DG; Kelly, J; Kiefl, RF; MacFarlane, WA; MacLachlan, M; McKenzie, I
    μSR and ALCR techniques have been used to investigate the structure and dynamics of the Mu-cyclohexadienyl radical interacting with Au and Pt metal nanoparticles (MNPs) supported in mesoporous silica (SBA-15). Surprisingly, coherent precession signals are observed and the isotropic hyperfine coupling constants are almost the same in loaded and unloaded samples, implying that the electronic structure of MuC6H6 is only weakly perturbed by the presence of the MNPs. We propose the observed radicals are shielded from the metallic surfaces by a benzene coating on the MNPs. The Δ1 resonance is observable in MNP-loaded samples at higher temperatures than in the unloaded SBA-15. This is attributed to stronger binding of MuC6H6 to the benzene coated MNPs.. © The Authors - Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
  • No Thumbnail Available
    Item
    Muon implantation of meltallocenes: ferrocene
    (Wiley-VCH Verlag Berlin, 2006-06-18) Jayasooriya, UA; Grinter, R; Hubbard, PL; Aston, GM; Stride, JA; Hopkins, GA; Camus, L; Reid, ID; Cottrell, SP; Cox, SFJ
    Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17 T, for the low-temperature phase at 18 K. The high-temperature phase at 295 K shows that only the last feature shifted down to about 0.49 T and a muon spin relaxation peak at about 0.106 T which approaches zero field when reaching the phase transition temperature of 164 K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe-Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the SR spectra of ferrocene was estimated to be 584 K. Correlation time for the ring rotation dynamics of the Fe-Mu radical at this temperature is 3.2 ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported. © 2006, Wiley-VCH Verlag Berlin
  • No Thumbnail Available
    Item
    Muon spin relaxation study of manganese hydroxy squarate
    (Elsevier, 2008-09-01) Mole, RA; Cottrell, SP; Stride, JA; Wood, PT
    Muon spin relaxation has been used to study the magnetic phase transition and spin dynamics above T-c in Mn-2(OH)(2)(C4O4). These studies confirm previous findings of a transition to long range order, providing a more accurate determination of T-c = 12.5 K as well as indicating short range order at temperatures above the phase transition. The muon measurements are insensitive to the presence of a small quantity of manganese carbonate in the sample that tend to dominate bulk magnetic susceptibility experiments. © 2008, Elsevier Ltd.
  • Thumbnail Image
    Item
    Spin depolarization of Muonium in Mesoporous Silica
    (IOP Publishing, 2014-12-16) Dehn, MH; Arseneau, DJ; Bridges, MD; Buck, T; Cortie, DL; Cottrell, SP; Fleming, DG; Kelly, JA; MacFarlane, WA; MacLachlan, MJ; Morris, GD; McKenzie, I; Xiao, J; Kiefl, RF
    We report muon spin rotation/relaxation measurements of muonium in mesoporous silica (SBA-15) with a high specific surface area of 600 m2/g. Up to 70 percent of the incoming muons form muonium and escape efficiently into the open pores at all temperatures between 3 and 300K. We present evidence that the interaction with the silica surfaces involves both spin exchange and a transition to a diamagnetic state, possibly due to dangling bonds on the surface. At very low temperatures, below 20K, the interaction between muonium and the silica surfaces is suppressed due to a He film coating the surfaces. These results indicate that it should be possible to use muonium to probe the surfaces of uncapped nanoparticles supported in silica. © 2014 The Authors - Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.