Synthesis of SmFeAsO by an easy and versatile route and its physical property characterization

Abstract

We report synthesis, structure, electrical transport, and heat capacity of SmFeAsO. The title compound is synthesized by one-step encapsulation of stoichiometric FeAs, Sm, and Sm 2 O 3 in an evacuated ͑10−5 Torr͒ quartz tube by prolong ͑72 h͒ annealing at 1100°C. The as-synthesized compound is crystallized in tetragonal structure with P4 / nmm space group having lattice parameters a = 3.937 26͑33͒ A and c = 8.498 02͑07͒ A. The resistance ͑R-T͒ measurements on the compound exhibited ground state spin-density-wave ͑SDW͒-like metallic steps below 140 K. Heat capacity C P ͑T͒ measurements on the title compound, showed an anomaly at around 140 K, which is reminiscent of the SDW ordering of the compound. At lower temperatures the C P ͑T͒ shows a clear peak at around 4.5 K. At lower temperature below 20 K, C p ͑T͒ is also measured under an applied field of 7 T. It is concluded that the C P ͑T͒ peak at 4.5 K is due to the antiferromagnetic ordering of Sm 3+ spins. These results are in confirmation with ordering of Sm in Sm 2−x Ce x CuO 4 .

Interplay of Sm4f and Co3d spins in SmCoAsO

“…It is clear that the C P (T)H is deviated from the zero field value at low temperatures below 20K. This is unlike the case of SmFeAsO, where there is nearly no change in C P (T)H under magnetic field [15]. This is precisely because unlike in present case of SmCoAsO, in SmFeAsO Co FM spins will depend upon the c-lattice parameter, i.e.…”

Evolution of superconductivity in PrFe1−Co AsO (x=0.0–1.0)

“…This anomaly in the resistivity is the result of the coupled structural phase transition from the tetragonal P4/nmm to the orthorhombic Cmma space group at around T~150 K, and the commensurate anti-ferromagnetic (AF) magnetic ordering of the Fe spins at a slightly lower temperature of ~140K, also called 'spin density wave' (SDW) like transition. [2][3][4][5][6][7][8][9]. An upward resistivity step at around 12 K is also observed, which could be clearly seen as a kink in d /dT plot, the same is not shown here as was recently reported by some of us elsewhere for the same sample, please see ref.…”

“…The most intriguing part is that these compounds contain familiar ferromagnetic Fe and yet exhibit superconductivity of up to above 55 K, which is second only to high T c cuprates [2][3][4][5][6][7]. The un-doped non superconducting ground state of these compounds i.e., REFeAsO show an anomaly in resistivity measurements below 150 K due to coupled crystallographic change and the spin density wave (SDW) like magnetic transition of Fe spins [2][3][4][5][6][7][8][9]. Superconductivity is achieved along with simultaneous suppression of crystallographic and magnetic phase transitions, by carrier doping via O site F substitution or vacancies in RE-O layer [2][3][4][5][6][7].…”

Synthesis, Electric Transport, Mossbauer Spectroscopy, Specific Heat and Induction of Superconductivity in ReFeAsO (Re=La, Pr, Gd and Sm)

“…After calculating the magnetic and non-magnetic contributions to C p by fitting of data in temperature range 12 K T 20 K [50], the temperature dependence of entropy associated with the magnetic transition was estimated from the C p mag (T). The magnetic entropy saturates at temperature above 4.5 K to a value 4.5 J/mole K.…”