  Superconducting poly- and single-crystalline samples of Sm1-xThxFeAsO with
partial substitution of Sm3+ by Th4+ were synthesized and grown under high
pressure and their structural, magnetic and transport properties are studied.
The superconducting Tc reaches values higher than 50 K. Bulk superconducting
samples (x = 0.08, 0.15, 0.3) do not show any signs of a phase transition from
tetragonal to orthorhombic crystal structure at low temperatures. With Th
substitution the unit cell parameters a and c shrink and the fractional atomic
coordinate of the As site zAs remains almost unchanged, while that of Sm/Th
zSm/Th increases. Upon warming from 5 K to 295 K the expansion of the FeAs
layer thickness is dominant, while the changes in the other structural building
blocks are smaller by a factor of 1/5, and they compensate each other, since
the As-Sm/Th distance appears to contract by about the same amount as the
O-Sm/Th expands. The poly- and single-crystalline samples are characterized by
a full diamagnetic response in low magnetic field, by a high intergrain
critical-current density for polycrystalline samples, and by a critical current
density of the order of 8 x 105 A/cm2 for single crystals at 2 K in fields up
to 7 T. The magnetic penetration depth anisotropy {\gamma}{\lambda} increases
with decreasing temperature, a similar behavior to that of SmFeAsO1-xFy single
crystals. The upper critical field estimated from resistance measurements is
anisotropic with slopes of 5.4 T/K (H//ab plane) and 2.7 T/K (H//c axis), at
temperatures sufficiently far below Tc. The upper critical field anisotropy
{\gamma}H is in the range of 2, consistent with the tendency of a decreasing
{\gamma}H with decreasing temperature, already reported for SmFeAsO1-xFy single
crystals.
