Doctor of Philosophy (PhD)


Physics and Astronomy

Document Type

Restricted Dissertation


The interactions between magnetic moments and electrons are essential in creating many of the unique properties of magnetic systems. In this thesis, I focused on two Fe-based systems employing multiple experimental techniques to investigate the coupling between localized magnetic moments and conducting charge carriers in two systems with tendencies to order into itinerant magnetic phases.\\ With systematic investigations of Fe$_{1-y}$Co$_y$Si, we discovered a field depended non-Fermi-Liquid (non-FL) behavior near its insulator-metal-transition (IMT) that appears to share the same mechanism as previously discovered in Mn doped FeSi - the underscreened Kondo effect.\\ A similar interaction of the charge carrier moments screening $S=1$ impurity moments are found in the $y\approx0.01$ range of Co doped FeSi as in Fe$_{1-x}$Mn$_x$Si. %From magnetic property study, we observed a systematic increase of the Weiss temperature from Mn doping to Co doping. And $\Theta_w$ remains negative in the very low doping range of Fe$_{1-y}$Co$_y$Si. We have also found that the impurity moment in the low doping range of the Fe$_{1-y}$Co$_y$Si is $S=1$, similar as in Mn doped Si. The conductivity results indicate a field dependent non-FL behavior at IMT of Fe$_{1-y}$Co$_y$Si that transitions to a disordered FL dependence with the application of magnetic field or by increasing the density of Co substitutions. However, a small region of Co-substitution between $0.01



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Committee Chair

DiTusa, John