We report the synthesis, structure, and magnetic and transport properties of a new ternary intermetallic compound PrRhSn${}_3$, which crystallizes in LaRuSn${}_3$-type cubic structure (space group $Pm\overline{3}n$). At low applied fields, the dc magnetic susceptibility exhibits a sharp anomaly below 6 K with an irreversible behavior in zero-field-cooled (ZFC) and field-cooled (FC) susceptibility below 5.5 K. The ac susceptibility exhibits a frequency-dependent anomaly, revealing a spin-glass behavior with a freezing temperature $T_f$ $=$ 4.3 K. The observation of spin-glass behavior is further supported by a very slow decay of thermoremnant magnetization (mean relaxation time $\tau$ $=$ 2149 s). However, a small jump at very low field in the isothermal magnetization at 2 K and a weak anomaly in the specific heat near 5.5 K reveal the presence of ferromagnetic clusters. The frequency dependence of the transition temperature $T_f$ in the ac susceptibility obeys the Vogel-Fulcher law $\nu ={\nu }_0\text{exp}[-E_a/k_{\mathrm{B}}(T_f-T_0)]$ with activation energy $E_a/k_{\mathrm{B}}$ $=$ 19.1 K. This, together with an intermediate value of the parameter $\delta T_f=\Delta T_f/T_f\Delta \left({\log }_{10}\nu \right)$ $=$ 0.086, provides an evidence for the formation of a cluster glass state in PrRhSn${}_3$. Further, we have analyzed the frequency dependence of transition temperature within the framework of critical slowing down, $\tau ={\tau }_0{[(T_f-T_{\mathrm{SG}})/T_{\mathrm{SG}})}^{-z{\nu }^{\prime }}]$, and found the characteristic time constant ${\tau }_0$ $=$ 2.04 $\times$ 10${}^{-10}$ s and critical exponent $z{\nu }^{\prime }$ $=$ 10.9, which also support a cluster spin-glass behavior in this compound. The magnetic contribution of the specific heat reveals a broad Schottky-type anomaly centered around 10 K, and the analysis based on the crystal-electric-field model indicates a singlet ground state. Further, below $T_f$, the magnetic part of the specific heat exhibits a $T^{3/2}$ temperature dependence. The strong influence of the crystal electric field and a $T^{3/2}$ temperature dependence are also seen in the electrical resistivity, which reveals a metallic character and a high magnetoresistance. We also obtain a surprisingly large value of Sommerfeld-Wilson ratio $R_{\mathrm{W}}\approx 247$.

We present synchrotron x-ray diffraction, neutron powder diffraction, and time-of-flight inelastic neutron scattering measurements on the rare earth pyrochlore oxide ${\mathrm{Nd}}_2{\mathrm{Zr}}_2{\mathrm{O}}_7$ to study the ordered state magnetic structure and cystal-field states. The structural characterization by high-resolution synchrotron x-ray diffraction confirms that the pyrochlore structure has no detectable O vacancies or Nd/Zr site mixing. The neutron diffraction reveals long-range all-in/all-out antiferromagnetic order below $T_{\mathrm{N}}\approx 0.4$ K with propagation vector k = (0 0 0) and an ordered moment of $1.26\left(2\right){\mu }_{\mathrm{B}}$/Nd at 0.1 K. The ordered moment is much smaller than the estimated moment of $2.65{\mu }_{\mathrm{B}}$/Nd for the local $\langle 111\rangle$ Ising ground state of ${\mathrm{Nd}}^{3+}$ $\left(J=9/2\right)$ suggesting that the ordering is partially suppressed by quantum fluctuations. The inelastic neutron scattering experiment further confirms the Ising anisotropic ground state of ${\mathrm{Nd}}^{3+}$ and also reveals its dipolar-octupolar character which possibly induces the quantum fluctuation. The crystal-field level scheme and ground state wave function have been determined.

Polycrystalline samples of LaNi${}_2$(Ge${}_{1-x}$P${}_x$)${}_2$ ($x=0,0.25,0.50,0.75,1$) were synthesized and their properties investigated by x-ray diffraction (XRD) measurements at room temperature and by heat capacity $C_{\mathrm{p}}$, magnetic susceptibility $\chi$, and electrical resistivity $\rho$ measurements versus temperature $T$ from 1.8 to 350 K. Rietveld refinements of powder XRD patterns confirm that these compounds crystallize in the body-centered-tetragonal ThCr${}_2$Si${}_2$-type structure (space group $I$4/mmm) with composition-dependent lattice parameters that slightly deviate from Vegard's law. The $\rho \left(T\right)$ measurements showed a positive temperature coefficient for all samples from 1.8 to 300 K, indicating that all compositions in this system are metallic. The low-$T$ $C_{\mathrm{p}}$ measurements yield a rather large Sommerfeld electronic specific heat coefficient $\gamma =12.4\left(2\right)$ mJ/mol K${}^2$ for $x=0$, reflecting a large density of states at the Fermi energy that is comparable with the largest values found for the $A$Fe${}_2$As${}_2$ class of materials with the same crystal structure. The $\gamma$ decreases approximately linearly with $x$ to 7.4(1) mJ/mol K${}^2$ for $x=1$. The $\chi$ measurements show nearly temperature-independent paramagnetic behavior across the entire range of compositions except for LaNi${}_2$Ge${}_2$, where a broad peak is observed at $\approx 300$ K from $\chi \left(T\right)$ measurements up to 1000 K that may arise from short-range antiferromagnetic correlations in a quasi-two-dimensional magnetic system. High-accuracy Padé approximants representing the Debye lattice heat capacity and Bloch-Grüneisen electron-phonon resistivity functions versus $T$ are presented and are used to analyze our experimental $C_{\mathrm{p}}\left(T\right)$ and $\rho \left(T\right)$ data, respectively, for $1.8\mathrm{K}\le T\le 300$ K. The $T$ dependences of $\rho$ for all samples are well-described over this $T$ range by the Bloch-Grüneisen model, although the observed $\rho (300$ K) values are larger than calculated from this model. A significant $T$ dependence of the Debye temperature determined from the $C_{\mathrm{p}}\left(T\right)$ data was observed for each composition. No clear evidence for bulk superconductivity or any other long-range phase transition was found for any of the LaNi${}_2$(Ge${}_{1-x}$P${}_x$)${}_2$ compositions studied.

We have investigated the superconducting properties of the noncentrosymmetric superconductor LaRhSi${}_3$ by performing magnetization, specific heat, electrical resistivity, and muon spin relaxation ($\mu$SR) measurements. LaRhSi${}_3$ crystallizes with the BaNiSn${}_3$-type tetragonal structure (space group $I4\hspace{0.5em}\mathit{mm}$), as confirmed through our neutron diffraction study. Magnetic susceptibility, electrical resistivity and specific heat data reveal a sharp and well-defined superconducting transition at $T_c=2.16\pm 0.08$ K. The low-temperature specific heat data reveal that LaRhSi${}_3$ is a weakly coupled bulk BCS superconductor and has an $s$-wave singlet ground state with an isotropic energy gap of $~$0.3 meV, $2{\Delta }_0/k_B{T}_c=3.24$. The specific heat data measured in an applied magnetic field strongly indicate a type I behavior. Type I superconductivity in this compound is also inferred from the Ginzburg-Landau parameter, $\kappa =0.25$. Various superconducting parameters, including the electron-phonon coupling strength, penetration depth, and coherence length, characterize LaRhSi${}_3$ as a moderate dirty-limit superconductor. A detailed study of the magnetic field-temperature ($H-T$) phase diagram is presented and from a consideration of the free energy, the thermodynamic critical field, $H_{c0}$, is estimated to be $17.1\pm 0.1$ mT, which is in very good agreement with that estimated from the transverse field $\mu$SR measurement that gives $H_{c0}=17.2\pm 0.1$ mT. The transverse field $\mu$SR results are consistent with conventional type I superconductivity in this compound. Further, the zero field $\mu$SR results indicate that time-reversal symmetry is preserved when entering the superconducting state, also supporting a singlet pairing superconducting ground state in LaRhSi${}_3$.

We have investigated the physical properties of a pyrochlore hafnate ${\mathrm{Nd}}_2{\mathrm{Hf}}_2{\mathrm{O}}_7$ using ac magnetic susceptibility ${\chi }_{\mathrm{ac}}\left(T\right)$, dc magnetic susceptibility $\chi \left(T\right)$, isothermal magnetization $M\left(H\right)$, and heat capacity $C_{\mathrm{p}}\left(T\right)$ measurements, and determined the magnetic ground state by neutron powder diffraction. An upturn is observed below 6 K in $C_{\mathrm{p}}\left(T\right)/T$, however both $C_{\mathrm{p}}\left(T\right)$ and $\chi \left(T\right)$ do not show any clear anomaly down to 2 K. The ${\chi }_{\mathrm{ac}}\left(T\right)$ shows a well-pronounced anomaly indicating an antiferromagnetic transition at $T_{\mathrm{N}}=0.55$ K. The long-range antiferromagnetic ordering is confirmed by neutron diffraction. The refinement of the neutron diffraction pattern reveals an all-in/all-out antiferromagnetic structure, where for successive tetrahedra the four ${\mathrm{Nd}}^{3+}$ magnetic moments point alternatively all-into or all-out-of the tetrahedron, with an ordering wave vector k = (0, 0, 0) and an ordered state magnetic moment of $m=0.62\left(1\right){\mu }_{\mathrm{B}}$/Nd at 0.1 K. The ordered moment is strongly reduced, reflecting strong quantum fluctuations in ordered state.

The compound ${\mathrm{BaMn}}_2{\mathrm{As}}_2$ with the tetragonal ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure is a local-moment antiferromagnetic insulator with a Néel temperature $T_{\mathrm{N}}=625\mathrm{K}$ and a large ordered moment $\mu =3.9{\mu }_{\mathrm{B}}/\mathrm{Mn}$. We demonstrate that this compound can be driven metallic by partial substitution of Ba by K while retaining the same crystal and antiferromagnetic structures together with nearly the same high $T_{\mathrm{N}}$ and large $\mu$. ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Mn}}_2{\mathrm{As}}_2$ is thus the first metallic ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$-type $M\mathrm{As}$-based system containing local $3d$ transition metal $M$ magnetic moments, with consequences for the ongoing debate about the local-moment versus itinerant pictures of the FeAs-based superconductors and parent compounds. The ${\mathrm{Ba}}_{1-x}{\mathrm{K}}_x{\mathrm{Mn}}_2{\mathrm{As}}_2$ class of compounds also forms a bridge between the layered iron pnictides and cuprates and may be useful to test theories of high $T_{\mathrm{c}}$ superconductivity.