RESUMO
Reentrance, the return of a system from an ordered phase to a previously encountered less-ordered one as a controlled parameter is continuously varied, is a recurring theme found in disparate physical systems, yet its microscopic cause is often not investigated thoroughly. Here, through detailed characterization and theoretical modeling, we uncover the microscopic mechanism behind reentrance in the strongly frustrated pyrochlore antiferromagnet Er_{2}Sn_{2}O_{7}. We use single crystal heat capacity measurements to expose that Er_{2}Sn_{2}O_{7} exhibits multiple instances of reentrance in its magnetic field B vs temperature T phase diagram for magnetic fields along three cubic high symmetry directions. Through classical Monte Carlo simulations, mean field theory, and classical linear spin-wave expansions, we argue that the origins of the multiple occurrences of reentrance observed in Er_{2}Sn_{2}O_{7} are linked to soft modes. These soft modes arise from phase competition and enhance thermal fluctuations that entropically stabilize a specific ordered phase, resulting in an increased transition temperature for certain field values and thus the reentrant behavior. Our work represents a detailed examination into the mechanisms responsible for reentrance in a frustrated magnet and may serve as a template for the interpretation of reentrant phenomena in other physical systems.
RESUMO
The title compound, calcium dimanganese tetraoxide, CaMn(2)O(4), was synthesized hydrothermally and is made up of edge-sharing Mn(3+) distorted octahedral layers and eight-coordinate Ca(2+) centered polyhedral layers.
RESUMO
A new mixed alkali/alkaline earth iron phosphate, NaBaFe4(HPO4)3.H2O, has been synthesized hydrothermally and structurally characterized by single-crystal X-ray diffraction, magnetic susceptibility, infrared spectroscopy, and thermogravimetric analysis. The title compound crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 9.287(2) A, b = 22.665(4) A, c = 8.966(3) A, beta = 91.82(2), and Z = 4. The compound has a 2-D framework structure constructed from layers, stacked along the [010] unit cell direction with Na+ and Ba2+ ions, and water molecules residing within the interlayer space. The anionic layers are composed from the assemblage of vertex shared FeO6 octahedra interconnected by PO4(3)- and HPO4(2)- tetrahedra. The layers are built from four unique FeO6 units linking through vertex shared oxygen atoms to form infinite zigzag chains that run parallel to the a axis. These chains form single layers that run infinitely in the c direction through the vertex sharing of PO4 groups.
