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INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION

Gebretsadik, Adane Samuel, Gebretsadik
http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816

Abstract Details

2018, PHD, Kent State University, College of Arts and Sciences / Department of Physics.
This dissertation presents a detailed study of the structural and magnetic properties of selected ferromagnetic alloys to probe the impact of "disorder" on quantum phase transition. The interplay between chemical and magnetic disorder close to a ferromagnetic quantum phase transition is investigated in the d-metal alloy Ni(1-x)V(x) and the f-metal alloys, CeT(1-x)Rh(x) (with T=Pd and Pt) by muon spin rotation (muSR) and wide-angle neutron scattering with pair distribution function (PDF) analysis. I present muon spin rotation (muSR) data and wide-angle neutron diffraction data with pair distribution function (PDF) analysis of two ferromagnetic alloys that can be driven to a paramagnetic phase by chemical substitution. Both systems, Ni(1-x)V(x), where the ferromagnetic order is suppressed at xc=0.116 and CeT(1-x)Rh(x) with xc>0.5 show indications that magnetic inhomogeneities play an important role for this quantum phase transition. muSR data of Ni(1-x)V(x) directly distinguishes finite magnetic clusters from long range magnetic order and therefore gives strong evidence for a quantum Griffiths phase extending into the ferromagnetic phase. Since the location of the V is crucial for creating the magnetic inhomogeneities, a structural investigation focusing on local pair correlations clarifies how much chemical disorder is present. It confirms that the Ni(1-x)V(x) powder samples up to x=0.15 crystallize in a random alloy fcc structure. Simulations of the local PDF with other models give inferior results. This strongly supports that in Ni-V the magnetic clusters originate from Ni-rich regions created from random occupation rather than from chemical clusters. The PDF analysis of the neutron data of the CeRh-alloys finds structural abnormalities that are directly related to magnetic inhomogeneities. All polycrystalline CeT(1-x)Rh(x) samples with 0.2< x<0.8 crystallize in the same CrB structure but show different additional phases in small concentrations. The change of lattice constants and atomic displacement parameters towards higher x indicate a large variation in Ce-Rh bond lengths. This disorder originates from the different Ce neighbor atoms, explaining nonmagnetic Ce impurities and variations in Kondo temperatures. In both systems, a direct relationship between chemical and magnetic structure is revealed that clarifies the origin of disorder for the ferromagnetic quantum phase transition.
Almut Schroeder (Advisor)
Carmen Almasan (Committee Member)
Mietek Jaroniec (Committee Member)
Maxim Dzero (Committee Member)
Robert J. Twieg (Committee Member)
122 p.
Physics
quantum phase transition; disorder; magnetic clusters; quantum Griffiths phase; neutron scattering; pair distribution function; muon spin rotation

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Citations

  • Gebretsadik, Gebretsadik, A. S. (2018). INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION [Doctoral dissertation, Kent State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816

    APA Style (7th edition)

  • Gebretsadik, Gebretsadik, Adane. INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION. 2018. Kent State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816.

    MLA Style (8th edition)

  • Gebretsadik, Gebretsadik, Adane. "INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION." Doctoral dissertation, Kent State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=kent1527609152939816

    Chicago Manual of Style (17th edition)

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© 2018, some rights reserved.Creative Commons License INTERPLAY BETWEEN CHEMICAL AND MAGNETIC DISORDER IN SELECTED ALLOYS CLOSE TO A FERROMAGNETIC QUANTUM PHASE TRANSITION by Adane Samuel Gebretsadik Gebretsadik is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by Kent State University and OhioLINK.