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Type of Document Dissertation Author Yeo, Sunmog Author's Email Address sunmog@magnet.fsu.edu URN etd-11112003-065129 Title Doping Effects on the Kondo Lattice Materials: FeSi, CeCoIn5, and YbInCu4 Degree Doctor of Philosophy Department Physics, Department of Advisory Committee
Advisor Name Title Zachary Fisk Committee Chair Jorge Piekarewicz Committee Member Naresh Dalal Committee Member Nicholas Bonesteel Committee Member Stephan von Molnar Committee Member Keywords
- Kondo Lattice
- Mixed Valence State
- Kondo Insulator
- Heavy Fermion Superconductor
Date of Defense 2003-11-04 Availability unrestricted Abstract We constructed the phase diagram through theanalysis of magnetic, thermal and transport measurements on single
crystals. The phase diagram shows a first-order transition from a
Kondo insulator (exponentially activated properties) to a
ferromagnetic metal at a critical concentration, $x_{
m c} sim
0.25$. The field dependence of the magnetization ($M(H)$) shows
that the saturation moment of $x = 0.27$ is 10 times larger than
that of $x = 0.24$. The spin gap of $x = 0.24$, 167K, is quite
close to the transition temperature of $x = 0.27$, 150K,
indicating that the characteristic energies of the two competing
phases, i.e. the Curie temperature and the spin gap of the Kondo
insulator, are essentially equal at the critical concentration.
For $x < x_{
m c}$, spin gap, transport gap and resistivity
minimum systematically decrease with increasing $x$. Saturation
moments and specific heat coefficients are almost zero for $x <
x_{
m c}$. The temperature dependence of magnetic susceptibility
($chi (T)$) for $x = 0.2$ shows a broad maximum around 200K,
indicating that the broad maximum temperature decreases with $x$
for $x < x_{
m c}$. The variable range hopping analysis suggests
the existence of the localized state for this region.
For $x > x_{
m c}$, the data break into two distinct regimes:
$x_{
m c} < x < sim 0.5$ and $sim 0.5 < x leq 1$. For $x_{
m
c} < x < sim 0.5$, $chi (T)$ does not displays a sharp
transition at $T_{
m c}$ and $M(H)$ increases with increasing
fields. The temperature dependence of the resistivity ($
ho (T)$)
shows metallic behavior. However, it does not have any kink at
$T_{
m c}$. In contrast, for $sim 0.5 < x leq 1$, $chi (T)$
displays a sharp transition at $T_{
m c}$ and $M(H)$ saturates at
$H sim 0.3$T. $
ho (T)$ has a kink at $T_{
m c}$. Based on the
Kondo insulator picture, we can explain the specific heat
coefficient $gamma$ evolution with $x$.
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