Evidence of magnetically driven structural phase transition inRFeAsO(R=La, Sm, Gd, and Tb): A low-temperature x-ray diffraction study

Structural and superconducting properties of LaFeAs1−x Sb x O1−y F y

“…Based on the method proposed by Klauss et al [26] , the critical temperatures associate with the structure phase transition (T S ) and SDW ordering (T N ) can be recognized as T S =157 K (144 K), T N =138 K (133 K) for x=0 (x=0.33), respectively. The decrease in the temperature difference between T S and T N (from 19 K to 11 K) is consistent with the thinning of the La 2 O 2 layers, which may strengthen the interlayer magnetic exchange coupling significantly [27,28] . To study whether Sb doping will influence the superconducting transition temperature, we take the fluorine doped LaFeAsO 0.9 F 0.1 superconductor as the starting compound.…”

Temperature dependence of resistivity of RFeAsO compounds

“…The overall behavior of q(T) for each sample is similar to the earlier reported data for RFeAsO [5,9,18], i.e., q(T) increases with the lowering of temperature down to a temperature T q (temperature corresponding to the cusp of q(T) curve), and it decreases rapidly below the cusp at T q . T q for each sample has been given in Table 1.…”

“…In the temperature range (200-165 K), q increases with the lowering of temperature reaching a maximum around T q = 165 K [18]. Similar behavior of increasing q(T) with the lowering of temperature down to almost 150 K has been observed for the polycrystalline samples of CeFeAsO, PrFeAsO, NdFeAsO [5] and SmFeAsO [9] although McGuire et al [5] consider the temperature variation of q(T) to be negligible in the tetragonal phase. Upon further cooling, q(T) drops sharply.…”

“…5, dq/dT has been claimed to show double-peaked structure for the samples CeFeAsO, PrFeAsO, NdFeAsO in addition to LaFeAsO. In explaining such double-peaked structure, one of the overlapping peaks has been associated with the crystallographic distortion and the other with the magnetic ordering [5] On the other hand, Luo et al [9] report single peak in each of the dq/dT versus T curves for polycrystalline LaFeAsO, SmFeAsO and GdFeAsO. The respective peak temperatures 132, 133, 128 K have been pointed out to be closer to AFM ordering temperatures rather than the SPT temperatures.…”

“…Regarding the origin of this antiferromagnetic (AFM) order, there are two propositions. One group identifies this order with the spin-density wave (SDW) [8] driven by Fermi surface nesting between the electron pockets at M point and hole pockets at C point based on band structural calculations, while the other group suggests that the AFM order originates from the short-range magnetic exchange coupling between local moments [9].…”