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The solid solution $\mathrm{Eu}{({\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Al}}_{x})}_{4}$ was grown in single crystal form to reveal a rich variety of crystallographic, magnetic, and electronic properties that differ from the isostructural end compounds ${\mathrm{EuGa}}_{4}$ and ${\mathrm{EuAl}}_{4}$, despite the similar covalent radii and electronic configurations of Ga and Al. Here we report the onset of magnetic spin reorientation and metamagnetic transitions for $x=0--1$ evidenced by magnetization and temperature-dependent specific heat measurements. ${T}_{\mathrm{N}}$ changes nonmonotonously with $x$, and it reaches a maximum around 20 K for $x=0.50$, where the $a$ lattice parameter also shows an extreme (minimum) value. Anomalies in the temperature-dependent resistivity consistent with charge density wave behavior exist only for $x=0.50$ and 1. Density functional theory calculations show increased polarization between the Ga-Al covalent bonds in the $x=0.50$ structure compared to the end compounds, such that crystallographic order and chemical pressure are proposed as the causes of the charge density wave behavior.

We present results from a numerical investigation of bilayer classical spin systems with local interactions and frustration caused by lattice geometry. We find that when two identical square planes are displaced by half a lattice constant in one direction, a transition to a uniformly twisted spin state occurs at ${J/J}_{\ensuremath{\perp}}g~0.25.$ An orthogonal state between layers is obtained in the limit $T=0$ and ${J}_{\ensuremath{\perp}}=0.$ If instead the two layers are offset along a diagonal, we obtain the phase diagram of the classical ${J}_{1}\ensuremath{-}{J}_{2}$ model. A weakly canted phase is observed at the classical transition point of ${J/J}_{\ensuremath{\perp}}=0.5,$ but frustration does not drive the system towards a state of orthogonal interlayer order. We propose a simple bilayer model with two inequivalent square lattices to study the frustrating interactions of the mixed layer pnictide oxides $({\mathrm{Sr}}_{2}{\mathrm{Mn}}_{3}{\mathrm{Pn}}_{2}{\mathrm{O}}_{2},\mathrm{ }\mathrm{Pn}=\mathrm{As},\mathrm{Sb}).$ We find a ground state composed of two independent N\'eel ordered layers when the interlayer exchange is an order of magnitude weaker than the intralayer exchange, as suggested by experiment. Evidence for local orthogonal order between the layers is found, but it occurs in regions of parameter space which are not experimentally realized.

The synthesis, crystal structure, magnetization, and resistivity of Gd-doped ${\mathrm{Eu}}_{14}{\mathrm{MnSb}}_{11}{,\mathrm{}\mathrm{Eu}}_{13.97}{\mathrm{Gd}}_{0.03}{\mathrm{MnSb}}_{11},$ are reported and compared to ${\mathrm{Eu}}_{14}{\mathrm{MnSb}}_{11}$ and ${\mathrm{Eu}}_{14}{\mathrm{MnBi}}_{11}.$ All three compounds are isostructural with the Zintl compound ${\mathrm{Ca}}_{14}{\mathrm{AlSb}}_{11}.$ The Gd-doped Eu transition metal Zintl compound crystallizes in the tetragonal space group ${I4}_{1}/\mathit{acd}$ with $a=17.338(3)\AA{}$ and $c=22.691(5)\AA{},$ where Gd partially replaces Eu in the structure. The compound displays three magnetic phase transitions: a ferromagnetic transition near 80 K, an apparent antiferromagnetic transition at a field-dependent ${T}_{N}$ ${(T}_{N}=30\mathrm{K}$ in zero field), and a spin-reorientation transition with a transition temperature that is near 15 K in zero field but is also field dependent. Measurements of both zero-field resistivity for $5l~Tl~300\mathrm{K}$ and the magnetoresistance in fields up to 5 T for the same temperatures are presented. Negative magnetoresistance is observed over a wide range of temperatures below 200 K.

Relatively large (up to 250 mg) single crystals of the intermetallic compound ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$ have been prepared by a flux-growth technique. The results of thermodynamic and transport measurements of these samples are presented. The compound orders ferromagnetically at approximately ${T}_{C}=53\ifmmode\pm\else\textpm\fi{}1\mathrm{K},$ with a magnetization consistent with the assignment ${\mathrm{Mn}}^{3+}$ ${(3d}^{4})$ and ${\mathrm{Yb}}^{2+}$ ${(4f}^{14}).$ The Mn moments are local in nature, with the full effective and saturated moment of the Hund's rule spin-only ground state. The electrical resistivity has a metallic temperature dependence, with only a modest anisotropy. Room-temperature values of the resistivity are relatively high for an intermetallic compound: $1630\ifmmode\pm\else\textpm\fi{}160\ensuremath{\mu}\ensuremath{\Omega}\mathrm{cm}$ and $1250\ifmmode\pm\else\textpm\fi{}130\ensuremath{\mu}\ensuremath{\Omega}\mathrm{cm}$ for currents flowing approximately parallel and perpendicular to the c axis, respectively. There is a distinct loss of spin-disorder scattering in the resistivity at ${T}_{C}.$ From the heat capacity, a rough estimation of the magnetic entropy gives $\ensuremath{\Delta}{S}_{M}\ensuremath{\approx}12.1\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K},$ the value in reasonable agreement with the expected $\ensuremath{\Delta}{S}_{M}\ensuremath{\approx}R\mathrm{ln}5$ from the assignment of these moments. All of these data are consistent with a picture of ${\mathrm{Mn}}^{3+}$ local moments being coupled via conduction electrons. To this end, ${\mathrm{Yb}}_{14}{\mathrm{MnSb}}_{11}$ appears to be analogous to local-moment rare-earth intermetallic compounds, and may point the way toward a class of $3d$ Kondo lattice compounds.

The magnetization and resistivity of single crystals of the Zintl compound ${\mathrm{Eu}}_{14}{\mathrm{MnBi}}_{11}$ are measured as functions of temperature and applied magnetic field. The magnetization data show an apparent antiferromagnetic transition at ${T}_{N}=32\mathrm{K}$ even though the high-temperature susceptibility suggests that the exchange coupling is ferromagnetic in nature. The zero-field resistivity is approximately independent of temperature above 32 K. Below 32 K the resistivity increases slightly and peaks at about 20 K before decreasing as the temperature is decreased. This temperature dependence is fairly normal for an antiferromagnetic metal. On the other hand, in contrast to other antiferromagnets, the single-crystal magnetoresistance is large and negative at all temperatures below about ${3T}_{N}.$ In addition, the dependence of the resistivity upon the magnetization is quite similar to the colossal-magnetoresistance materials.

The density of phonon states in the thermoelectric material Yb${}_{14}$MnSb${}_{11}$ has been studied first by inelastic neutron scattering and second in an element-specific way by nuclear inelastic x-ray scattering. The low sound velocity of 1880(50) m/s as obtained from the density of phonon states can be identified as an important reason for the low heat transport in this system. The high melting temperature of Yb${}_{14}$MnSb${}_{11}$ contrasts with the low energy of all phonons ($l$25 meV) and relates to an unusual lack of softening of phonon modes with temperature, when comparing the phonon density of states observed at ambient temperatures and at 1200 K. We have also measured the density of phonon states of the related Eu${}_{14}$MnSb${}_{11}$ compound and of the thermoelectric Zintl phase Zn${}_{4}$Sb${}_{3}$ in order to compare with related thermodynamic properties of Yb${}_{14}$MnSb${}_{11}$ and to elucidate the different mechanisms of the heat conductivity reduction in Zintl phases.

Measurements of the temperature dependence of the magnetic susceptibility of ${\mathrm{Sr}}_{14}$${\mathrm{MnAs}}_{11}$ were made from ambient pressure to P\ensuremath{\le}20 kbars. At ambient pressure this compound is known to be a semiconductor with a Curie susceptibility down to as low as 5 K. It is found that raising the pressure to 7 kbars enhances the susceptibility somewhat and that at pressures above 10--11 kbars the susceptibility is enhanced by more than an order of magnitude and an ordered magnetic state occurs with a transition temperature that increases as the pressure is increased. This suggests that the applied pressure leads to a band-crossing transition from semiconductor to metal and a consequent exchange coupling of the Mn spins.

The recently discovered ${\text{CaFe}}_{4}{\text{As}}_{3}$ system displays low-temperature Fermi-liquid behavior, with enhanced electron-electron correlations. At high temperatures, the magnetic susceptibility shows Curie-Weiss behavior, with a large temperature-independent contribution. Antiferromagnetic ordering is observed below ${T}_{N}=(88.0\ifmmode\pm\else\textpm\fi{}1.0)\text{ }\text{K}$, possibly via a spin density wave transition. A remarkably sharp drop in resistivity occurs below ${T}_{2}=(26.4\ifmmode\pm\else\textpm\fi{}1.0)\text{ }\text{K}$, correlated with a similarly abrupt increase in the susceptibility but no visible feature in the specific heat. The electronic specific-heat coefficient $\ensuremath{\gamma}$ at low temperatures is close to $0.02\text{ }\text{J}\text{ }{\text{mol}}_{\text{Fe}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2}$, but a higher value for $\ensuremath{\gamma}\ensuremath{\sim}0.08\text{ }\text{J}\text{ }{\text{mol}}_{\text{Fe}}^{\ensuremath{-}1}\text{ }{\text{K}}^{\ensuremath{-}2}$ can be inferred from a linear $Cp/T$ vs ${T}^{2}$ just above ${T}_{2}$. The Kadowaki-Woods ratio $A/{\ensuremath{\gamma}}^{2}=55\ensuremath{\ast}{10}^{\ensuremath{-}5}\text{ }\ensuremath{\mu}\ensuremath{\Omega}\text{ }\text{cm}\text{ }{\text{mol}}^{2}\text{ }{\text{K}}^{2}\text{ }{\text{mJ}}^{\ensuremath{-}2}$ is nearly two orders of magnitude larger than that of heavy fermions.

The magnetic, thermal, and transport properties of single crystals of the narrow gap semiconductor Ce3Au3Sb4 have been studied. Transport data are consistent with an exponential activation and variable range hopping at low temperatures, which is characteristic of weak disorder and localization. The specific heat and the magnetic susceptibility data suggest the existence of a large density of states of localized states in the gap. The physics is then different from standard Kondo insulators. From its unique physical properties, we propose a three band model valence, conduction, and f bands with weak disorder that explains most of the experimental findings.

Measurements of specific heat, magnetic susceptibility, electrical resistivity, and penetration depth have been performed on $\mathrm{Ce}\mathrm{Co}{\mathrm{In}}_{5\ensuremath{-}x}{\mathrm{Sn}}_{x}$ $(0\ensuremath{\leqslant}x\ensuremath{\leqslant}0.24)$ single crystals. The suppression of superconductivity and the decrease of the specific heat jump at ${T}_{c}$, $\ensuremath{\Delta}C∕{T}_{c}$, with increasing Sn concentration, and the power-law temperature dependence of penetration depth are consistent with impurity scattering calculated within the Abrikosov-Gorkov formalism indicating $d$-wave superconductivity in $\mathrm{Ce}\mathrm{Co}{\mathrm{In}}_{5\ensuremath{-}x}{\mathrm{Sn}}_{x}$. The non-Fermi liquid behavior [$C∕T\ensuremath{\sim}\ensuremath{-}\mathrm{ln}\phantom{\rule{0.2em}{0ex}}T$ and $\ensuremath{\rho}(T)\ensuremath{\sim}T$] observed in the normal state in zero magnetic field is quite robust against Sn substitution (and a variety of other tuning parameters), suggesting quantum criticality involving itinerant $f$-electrons in this system.

``14-1-11'' phase compounds, based on magnetic Mn ions and typified by ${\mathrm{Ca}}_{14}{\mathrm{MnBi}}_{11}$ and ${\mathrm{Ba}}_{14}{\mathrm{MnBi}}_{11},$ show an unusual magnetic behavior, but the large number (104) of atoms in the primitive cell has precluded any previous full electronic structure study. Using an efficient, local-orbital-based method within the local-spin-density approximation to study the electronic structure, we find a gap between a bonding valence-band complex and an antibonding conduction-band continuum. The bonding bands lack one electron per formula unit of being filled, making them low carrier density p-type metals. The hole resides in the ${\mathrm{MnBi}}_{4}$ tetrahedral unit, and partially compensates for the high-spin ${d}^{5} \mathrm{Mn}$ moment, leaving a net spin near $4{\ensuremath{\mu}}_{B}$ that is consistent with experiment. These manganites are composed of two disjoint but interpenetrating ``jungle gym'' networks of spin-$\frac{4}{2}$ ${\mathrm{MnBi}}_{4}^{9\ensuremath{-}}$ units with ferromagnetic interactions within the same network, and weaker couplings between the networks whose sign and magnitude is sensitive to materials parameters. ${\mathrm{Ca}}_{14}{\mathrm{MnBi}}_{11}$ is calculated to be ferromagnetic as observed, while for ${\mathrm{Ba}}_{14}{\mathrm{MnBi}}_{11}$ (which is antiferromagnetic) the ferromagnetic and antiferromagnetic states are calculated to be essentially degenerate. The band structure of the ferromagnetic states is very close to half metallic.