Strongly frustrated magnetism of the metallic pyrochlore oxide ${\mathrm{Pr}}_2{\mathrm{Ir}}_2{\mathrm{O}}_7$ has been revealed by single crystal study. While Pr $4f$ moments have an antiferromagnetic RKKY interaction energy scale of $|T^{*}|=20\mathrm{K}$ mediated by Ir $5d$-conduction electrons, no magnetic long-range order is found except for partial spin freezing at 120 mK. Instead, the Kondo effect, including a $\ln T$ dependence in the resistivity, emerges and leads to a partial screening of the moments below $|T^{*}|$. Our results indicate that the underscreened moments show spin-liquid behavior below a renormalized correlation scale of 1.7 K.

We have synthesized polycrystalline samples of the noncentrosymmetric superconductor Mo3Al2C by arc and RF melting, measured its transport, magnetic and thermodynamic properties, and computed its band structure. Experimental results indicate a bulk superconducting transition at Tc$\sim${}9.2$\hskip0.3em${}K while the density of states at the Fermi surface is found to be dominated by Mo\,d orbitals. Using the measured values for the lower critical field Hc1, upper critical field Hc2, and the specific heat C, we estimated the thermodynamic critical field Hc(0), coherence length $\xi${}(0), penetration depth $\lambda${}(0), and the Ginzburg-Landau parameter $\kappa${}(0). The specific-heat jump at Tc, $\Delta${}C/$\gamma${}Tc=2.14, suggests that Mo3Al2C is moderately to strongly coupled, consistent with the fast opening of the gap, as evidenced by the rapid release of entropy below Tc from our electronic specific-heat measurements. Above 2 K the electronic specific heat exhibits the power-law behavior, suggesting that synthesis of single crystals and measurements at lower temperature are needed to establish whether the gap is anisotropic. The estimated value of the upper critical field Hc2(0) is close to the calculated Pauli limit, therefore further studies are needed to determine whether the absence of an inversion center results in a significant admixture of the triplet component of the order parameter.

A remarkable decrease of the structural transition temperature of MnNiSi from 1200 to < 300 K by chemically alloying it with MnFeGe results in a coupling of the magnetic and structural transitions, leading to a large magnetocaloric effect near room temperature. Application of relatively low hydrostatic pressures (∼2.4 kbar) lead to an extraordinary enhancement of the isothermal entropy change from $-\Delta S=44$ to 89 $\mathrm{J}/\mathrm{kg}$ K at ambient and 2.4 kbar applied pressures, respectively, for a field change of $\Delta B=5\mathrm{T}$, and is associated with a large relative volume change of about 7% with $P=2.4$ kbar.