Spin density wave anomaly at 140 K in the ternary iron arsenide BaFe2As2

The ternary iron arsenide BaFe2As2 with the tetragonal ThCr2Si2-type structure exhibits a spin density wave (SDW) anomaly at 140 K, very similar to LaFeAsO, the parent compound of the iron arsenide superconductors. BaFe2As2 is a poor Pauli-paramagnetic metal and undergoes a structural and magnetic phase transition at 140 K, accompanied by strong anomalies in the specific heat, electrical resistance and magnetic susceptibility. In the course of this transition, the space group symmetry changes from tetragonal (I4/mmm) to orthorhombic (Fmmm). 57Fe Moessbauer spectroscopy experiments show a single signal at room temperature and full hyperfine field splitting below the phase transition temperature (5.2 T at 77 K). Our results suggest that BaFe2As2 can serve as a new parent compound for oxygen-free iron arsenide superconductors.Comment: 4 pages, 6 figures, submitted to PR

Optimization of the carrier concentration in phase-separated half-Heusler compounds

Inspired by the promising thermoelectric properties of phase-separated half-Heusler materials, we investigated the influence of electron doping in the n-type Ti_(0.3−x)Zr_(0.35)Hf_(0.35)NiSn compound. The addition of Nb to this compound led to a significant increase in its electrical conductivity, and shifted the maximum Seebeck coefficient to higher temperatures owing to the suppression of intrinsic carriers. This resulted in an enhancement of both the power factor α^2σ and figure of merit, zT. The applicability of an average effective mass model revealed the optimized electron properties for samples containing Nb. There is evidence in the literature that the average effective mass model is suitable for estimating the optimized carrier concentration of thermoelectric n-type half-Heusler compounds

Multi-resolution analysis for region of interest extraction in thermographic, nondestructive evaluation

Infrared Non-Destructive Testing (INDT) is known as an effective and rapid method for nondestructive inspection. It can detect a broad range of near-surface structuring flaws in metallic and composite components. Those flaws are modeled as a smooth contour centered at peaks of stored thermal energy, termed Regions of Interest (ROI). Dedicated methodologies must detect the presence of those ROIs. In this paper, we present a methodology for ROI extraction in INDT tasks. The methodology deals with the difficulties due to the non-uniform heating. The non-uniform heating affects low spatial/frequencies and hinders the detection of relevant points in the image. In this paper, a methodology for ROI extraction in INDT using multi-resolution analysis is proposed, which is robust to ROI low contrast and non-uniform heating. The former methodology includes local correlation, Gaussian scale analysis and local edge detection. In this methodology local correlation between image and Gaussian window provides interest points related to ROIs. We use a Gaussian window because thermal behavior is well modeled by Gaussian smooth contours. Also, the Gaussian scale is used to analyze details in the image using multi-resolution analysis avoiding low contrast, non-uniform heating and selection of the Gaussian window size. Finally, local edge detection is used to provide a good estimation of the boundaries in the ROI. Thus, we provide a methodology for ROI extraction based on multi-resolution analysis that is better or equal compared with the other dedicate algorithms proposed in the state of art

New thermodynamic data for CoTiO3, NiTiO3 and CoCO3 based on low-temperature calorimetric measurements

The low-temperature heat capacities of nickel titanate (NiTiO3), cobalt titanate (CoTiO3), and cobalt carbonate (CoCO3) were measured between 2 and 300 K, and thermochemical functions were derived from the results. Our new data show previously unknown low-temperature lambda-shaped heat capacity anomalies peaking at 37 K for CoTiO3 and 26 K for NiTiO3. From our data we calculate standard molar entropies (298.15 K) for NiTiO3 of 90.9 ± 0.7 J mol-1 K-1 and for CoTiO3 of 94.4 ± 0.8 J mol-1 K-1. For CoCO3, we find only a small broad heat capacity anomaly, peaking at about 31 K. From our data, we suggest a new standard entropy (298.15 K) for CoCO3 of 88.9 ± 0.7 J mol-1 K-1

Unusually short Ce-Ru distances in CeRuAl and related compounds

The aluminide CeRuAl with orthorhombic LaNiAl-type structure contains two crystallographically independent cerium sites which both exhibit relatively short Ce–Ru distances, i. e. 280 – 302 pm for Ce1 and 286 – 310 pm for Ce2. Susceptibility measurements show intermediate valence behavior of the cerium atoms (1.19(1) μB per formula unit) and no magnetic ordering down to 2 K. Chemical bonding analysis reveals a non-magnetic ground state and strong Ce–Ru bonding. The Ce–Ru bonding peculiarities of CeRuAl are discussed in line with those of other binary and ternary cerium–ruthenium compounds

The Solid Solutions Gd2Cu2In1-xMgx - Drastic Increase of the Curie Temperature upon In/Mg Substitution

The Mo2B2Fe-type intermetallic compounds Gd2Cu2In and Gd2Cu2Mg form a complete set of solid solutions Gd2Cu2In1-xMgx. The a lattice parameter, the Weiss constant and the Curie temperature increase with increasing magnesium content in an almost Vegard-like manner, while the c parameter remains almost constant. All members of the solid solutions show ferromagnetism with T(C)s between 114 and 80 K

Large reversible magnetocaloric effect due to a rather unstable antiferromagnetic ground state in Er4NiCd

Er4NiCd crystallizes with the Gd4RhIn type structure, space group F (4) over bar 3m, a=1333.3 pm. The nickel atoms have trigonal prismatic rare earth coordination. Condensation of the NiEr6 prisms leads to a three-dimensional network which leaves voids that are filled by regular Cd-4 tetrahedra. Er4NiCd shows Curie-Weiss behavior above 50 K with T-N=5.9 K. At field strength of 4 kOe a metamagnetic step is visible, together with the positive paramagnetic Curie-temperature (7.5 K) indicative for the rather unstable antiferromagnetic ground state. Therefore, a large reversible magnetocaloric effect (MCE) near the ordering temperature occurs and the values of the maximum magnetic-entropy change -Delta S-M(max) reach 18.3 J kg(-1) K-1 for the field change of 5 T with no obvious hysteresis loss around 17 K. The corresponding RCP of 595 J kg(-1) is relatively high as compared to other MCE materials in that temperature range. These results indicate that Er4NiCd could be a promising system for magnetic refrigeration at temperatures below liquid H-2. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3518556