arXiv subjects

T. A. Sayles

Publications and source records attributed to T. A. Sayles.

21 records · Page 2Linked to original sources

arXiv2005

Ferromagnetism and possible heavy fermion behavior in single crystals of NdOs$_4$Sb$_{12}$

Single crystals of the filled-skutterudite compound NdOs$_4$Sb$_{12}$ have been investigated by means of electrical resistivity, magnetization, and specific heat measurements. The NdOs$_4$Sb$_{12}$ crystals have the LaFe$_4$P$_{12}$-type cubic structure with a lattice parameter of 9.3 Å. Possible heavy-fermion behavior is inferred from specific heat measurements, which reveal a large electronic specific heat coefficient $γ\approx 520$ mJ/mol-K$^2$, corresponding to an effective mass $m^* \sim$ 98 $m_e$. Features related to a ferromagnetic transition at {$\sim$ 0.9 K} can be observed in electrical resistivity, magnetization and specific heat. Conventional Arrott-plot analysis indicates that NdOs$_4$Sb$_{12}$ conforms to mean-field ferromagnetism.

cond-mat.str-el↗

arXiv2004

Heavy Fermion Behavior, Crystalline Electric Field Effects, and Weak Ferromagnetism in SmOs_{4}Sb_{12}

The filled skutterudite compound SmOs_{4}Sb_{12} was prepared in single crystal form and characterized. The SmOs_{4}Sb_{12} crystals have the LaFe_{4}P_{12}-type structure with lattice parameter a = 9.3085 Angstroms. Specific heat measurements indicate a large electronic specific heat coefficient of ~880 mJ/mol K^{2}, from which an enhanced effective mass m^{*} ~ 170 m_{e} is estimated. The specific heat data also suggest crystalline electric field (CEF) splitting of the Sm^{3+} J = 5/2 multiplet into a Gamma_{7} doublet ground state and a Gamma_{8} quartet excited state separated by 37 K. Electrical resistivity rho(T) measurements reveal a decrease in rho(T) below ~50 K that is consistent with CEF splitting of ~33 K between a Gamma_(7) doublet ground state and Gamma_{8} quartet excited state. Specific heat and magnetic susceptibility measurements display a possible weak ferromagnetic transition at ~2.6 K, which could be an intrinsic property of SmOs_4Sb_{12} or possibly due to an unknown impurity phase.

cond-mat.str-el↗

arXiv2004

Evolution of crystalline electric field effects, superconductivity, and heavy fermion behavior in the specific heat of Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$

Specific heat $C(T)$ measurements were made on single crystals of the superconducting filled skutterudite series Pr(Os$_{1-x}$Ru$_x$)$_4$Sb$_{12}$ down to 0.6 K. Crystalline electric field fits in the normal state produced parameters which were in agreement with previous measurements. Bulk superconductivity was observed for all values of the Ru concentration $x$ with transition temperatures consistent with previous experiments, confirming a minimum in $T_{c}$ at $x=0.6$. The $C(T)$ data below $T_{c}$ appear to be more consistent with power law behavior for $x=0$ (PrOs$_4$Sb$_{12}$), and with exponential behavior for $0.05 \leq x \leq 0.2$. An enhanced electronic specific heat coefficient $γ$ was observed for $x \leq 0.4$, further supporting $x \simeq 0.6$ as a critical concentration where the physical properties abruptly change. Significant enhancement of $ΔC/T_{c}$ above the weak coupling value was only observed for $x=0$ and $x=0.05$.

cond-mat.supr-con↗