18 research outputs found
Structure and magnetic properties of the Ho2Ge2O7 pyrogermanate
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 crystal 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
Chemical Instability of the Cobalt Oxyhydrate Superconductor under Ambient Conditions
The layered sodium cobalt oxyhydrate superconductor Na0.3CoO2*1.4H2O is shown
through X-ray diffraction and thermogravimetric studies to be one of a series
of hydrated phases of Na0.3CoO2. Further, it is shown that the material is
exceptionally sensitive to both temperature and humidity near ambient
conditions, easily dehydrating to a non-superconducting lower hydrate. The
observation of this stable lower hydrate with c=13.8 angstroms implies that the
superconductivity turns on in this system between CoO2 layer spacings of 6.9
and 9.9 angstroms at nominally constant chemical doping.Comment: 10 pages and 4 figure