STUDY OF ATOMIC AND MAGNETIC CORRELATIONS IN FERROMAGNETIC NI-ALLOYS

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HIND AHMED ABDU ADAWI
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Saudi Digital Library
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The study of quantum phase transitions is a promising route for understanding the origin of unusual properties in strongly correlated electron systems. Recent theories predict a new quantum critical point (QCP) with exotic properties such as an observable quantum Griffiths phase in disordered itinerant systems. Previous studies on disordered ferromagnetic (FM) system Ni1−xVx showed only “signs” of magnetic clusters close to the critical concentration xc where FM is destroyed. This dissertation provides direct evidence of magnetic correlations at various length scales and fluctuations at different time scales close to the QCP using Ni-V and Ni-Cr samples. Polarized small-angle neutron scattering (SANS) measurements reveal short-range magnetic correlations in Ni-V samples close to QCP. This polarization study also supports long-range magnetic correlations within macroscopic domains. The structure characterization of Ni-Cr confirms a high-quality chemical structure with random atomic distribution after optimizing the annealing protocol. Muon spin rotation (µSR) measurements successfully show the advantage of Ni-Cr. The response is not dominated by any strong nuclear moment like Ni-V. The µSR asymmetry of Ni1−xCrx close to xc reveals magnetic order at low temperatures with coexisting dynamic clusters. Both SANS and µSR measurements support that the long-range FM order and short-range fluctuations are present in FM alloys Ni-V and Ni-Cr close to QCP.
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