The newly discovered CaFe$_4$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-independen
t contribution. Antiferromagnetic ordering is observed below T$_N$ = (88.0 $pm$ 1.0) K, possibly via a spin density wave (SDW) transition. A remarkably sharp drop in resistivity occurs below T$_2$ = (26.4 $pm$ 1.0) K, correlated with a similarly abrupt increase in the susceptibility, but no visible feature in the specific heat. The electronic specific heat coefficient $gamma$ at low temperatures is close to 0.02 J mol$^{-1}_{Fe}$ K$^{-2}$, but a higher value for $gamma$ ($sim$0.08 J mol$^{-1}_{Fe}$ K$^{-2}$ can be inferred from a linear C$ / $T textit{vs.} T$^2$ just above T$_2$. The Kadowaki-Woods ratio A$/gamma^2$ = 55$*10^{-5}$ $mu Omega$cm mol$^2$ K$^2 $mJ$^{-2}$ is nearly two orders of magnitude larger than that of heavy fermions.
We report the anisotropic magnetic properties of Ho2Ge2O7 determined from dc and ac magnetization, specific heat and powder neutron diffraction experiments. The magnetic lanthanide sublattice, seen in our refinement of the tetragonal pyrogermanate cr
ystal structure, is a right-handed spiral of edge-sharing and corner-sharing triangles; the local Ho-O coordination indicates that the crystal field is anisotropic. Susceptibility and magnetization data indeed show that the magnetism is highly anisotropic, and the magnetic structure has the Ho moments confined to the plane perpendicular to the structural spiral. The ordered moment of Ho3+, as determined from refinement of the neutron diffraction data, is 9.0 mu_B. Magnetic ordering occurs around 1.6 K. Temperature and field dependent ac susceptibility measurements show that this compound displays spin relaxation phenomena analogous to what is seen in the spin ice pyrochlore system Ho2Ti2O7.
Mn3V2O8 is a magnetic system in which S = 5/2 Mn2+ is found in the kagome staircase lattice. Here we report the magnetic phase diagram for temperatures above 2 K and applied magnetic fields below 9 T, characterized by measurements of the magnetizatio
n and specific heat with field along the three unique lattice directions. At low applied magnetic fields, the system first orders magnetically below Tm1 ~ 21 K, and then shows a second magnetic phase transition at Tm2 ~ 15 K. In addition, a phase transition that is apparent in specific heat but not seen in magnetization is found for all three applied field orientations, converging towards Tm2 as H -> 0. The magnetic behavior is highly anisotropic, with critical fields for magnetic phase boundaries much higher when the field is applied perpendicular to the Kagome staircase plane than when applied in-plane. The field-temperature (H - T) phase diagrams are quite rich, with 7 distinct phases observed.
