Phase transitions in LaFeAsO: Structural, magnetic, elastic, and transport properties, heat capacity and Mössbauer spectra

Abstract

We present results from a detailed experimental investigation of LaFeAsO, the parent material in the series of "FeAs" based oxypnictide superconductors. Upon cooling, this material undergoes a tetragonalorthorhombic crystallographic phase transition at ϳ160 K followed closely by an antiferromagnetic ordering near 145 K. Analysis of these phase transitions using temperature dependent powder x-ray and neutrondiffraction measurements is presented. A magnetic moment of ϳ0.35 B per iron is derived from Mössbauer spectra in the low-temperature phase. Evidence of the structural transition is observed at temperatures well above the transition temperature ͑up to near 200 K͒ in the diffraction data as well as the polycrystalline elastic moduli probed by resonant ultrasound spectroscopy measurements. The effects of the two phase transitions on the transport properties ͑resistivity, thermal conductivity, Seebeck coefficient, and Hall coefficient͒, heat capacity, and magnetization of LaFeAsO are also reported, including a dramatic increase in the magnitude of the Hall coefficient below 160 K. The results suggest that the structural distortion leads to a localization of carriers on Fe, producing small local magnetic moments which subsequently order antiferromagnetically upon further cooling. Evidence of strong electron-phonon interactions in the high-temperature tetragonal phase is also observed.

Monte Carlo study of the spin transport in magnetic materials

“…Let us say it again in another manner: the absence of a peak at the transition is due to the fact that the motion of an itinerant spin depends on its immediate environment: in ferromagnets, the variation of its energy ∆E going from a "parallel" cluster to a nearby "defect" (or antiparallel) cluster is much larger than the energy variation going from a cluster of antiferromagnetic ordering to a cluster which is a defect but a defect with an antiferromagnetic structure in the SC antiferromagnetic case. The smaller ∆E gives rise to a larger spin mobility i. e. a smaller R. Note that experimental data show just a shoulder in antiferromagnetic LaFeAsO [16].…”

“…Experiments on various magnetic materials have found in particular an anomalous behavior of the resistivity at the critical temperature where the system undergoes the ferromagnetic-paramagnetic phase transition [2][3][4][5][6]. Very recent experiments such as those performed on ferromagnetic SrRuO 3 thin films [9], superconducting BaFe 2 As 2 single crystals [10], La 1−x Sr x MnO 3 [11], Mn 1−x Cr x Te [12] and other compounds [13][14][15][16] show different forms of anomaly of the magnetic resistivity at the transition temperature. de Gennes and Friedel's first explanation in 1958 [17] for the resistivity behavior near T c was based on the interaction between the spins of conduction electrons and the lattice spins.…”

Suppression of spin density wave by isoelectronic substitution in

“…The transition is accompanied by a decrease in the Hall coefficient R H , as observed in other 1111-materials. [12,31] The vertical scale is truncated to emphasize the behavior of the Ru-containing materials. For x = 0, R H reaches a maximum negative value of 0.18 cm 3 C −1 at 5 K, in agreement with our previous report.…”

Superconductivity by transition metal doping in Ca10(Fe1−xMxAs)10(Pt3As8) (M= Co, Ni, Cu)

“…In conclusion we have demonstrated bulk superconductivity in the 1038 compounds Ca 10 (Fe 1−x M x As) 10 Superconducting properties in both compounds were evidenced by ac-and dcsusceptibility as well as dc-resistivity data. Moreover no superconductivity was evident in Cu-doped samples Ca 10 (Fe 1−x Cu x As) 10 (Pt 3 As 8 ).…”

“…Relationships between the magneto-structural phase transition and superconductivity in iron arsenides have intensively been studied [5,[8][9][10][11][12][13][14]. In 2011 the new superconductors Ca 10 (Fe 1−x Pt x As) 10 (Pt 3 As 8 ) (1038 phase, space group P 1) and polymorphic Ca 10 (FeAs) 10 (Pt 4 As 8 ) (1048-phases, space groups P 4/n, P 2 1 /n, P 1) with critical temperatures up to 35 K were discovered [15][16][17]. This new class recently expanded by analogous compounds with iridium (Ir1048) [18] and palladium (Pd1038) [19] instead of platinum.…”