Browsing by Author "Cottrell, SP"

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    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.
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    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
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    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.