Crystallography and physical properties of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">BaCo</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">As</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mo>,</mml:mo><mml:msub><mml:mi mathvariant="normal">Ba</mml:mi><mml:mrow><mml:mn>0.94</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant="normal">K</mml:mi><mml:mrow><mml:mn>0.06</mml:mn></mml:mrow></mml:msub><mml:msub><mml:mi mathvariant

“…These pnictides include metallic Co-based [7][8][9][10][11][12][13][14][15], itinerant AFM Cr-based [16][17][18][19][20][21][22][23][24], semiconducting AFM Mn-based [25][26][27][28][29][30][31][32][33], and superconducting Ni-based [34][35][36][37] compounds.…”

Section: Introductionmentioning

confidence: 99%

Antiferromagnetism in semiconductingSrMn2Sb2andBaMn2Sb2single crystals

et al. 2018

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Crystals of SrMn 2 Sb 2 and BaMn 2 Sb 2 were grown using Sn flux and characterized by powder and singlecrystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ , heat capacity C p , and magnetic susceptibility χ measurements versus temperature T , and magnetization versus field M ( H ) isotherm measurements. SrMn 2 Sb 2 adopts the trigonal CaAl 2 Si 2 -type structure, whereas BaMn 2 Sb 2 crystallizes in the tetragonal ThCr 2 Si 2 -type structure. The ρ ( T ) data indicate semiconducting behaviors for both compounds with activation energies of ≳ 0.35 eV for SrMn 2 Sb 2 and 0.16 eV for BaMn 2 Sb 2 . The χ ( T ) and C p ( T ) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2 Sb 2 and 450 K for BaMn 2 Sb 2 . The anisotropic χ ( T ≤ T N ) data also show that the ordered moments in SrMn 2 Sb 2 are aligned in the hexagonal a b plane, whereas the ordered moments in BaMn 2 Sb 2 are aligned collinearly along the tetragonal c axis. The a b -plane M ( H ) data for SrMn 2 Sb 2 exhibit a continuous metamagnetic transition at low fields 0 < H ≲ 1 T, whereas BaMn 2 Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ ( T ) and C p ( T ) data for both SrMn 2 Sb 2 and BaMn 2 Sb 2 indicate strong dynamic short-range AFM correlations above their respective T N up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the CaAl 2 Si 2 and ThCr 2 Si 2 crystal structures show that the T N values for the CaAl 2 Si 2 -type compounds are much smaller than those for the ThCr 2 Si 2 -type materials. Crystals of SrMn 2 Sb 2 and BaMn 2 Sb 2 were grown using Sn flux and characterized by powder and singlecrystal x-ray diffraction, respectively, and by single-crystal electrical resistivity ρ, heat capacity C p , and magnetic susceptibility χ measurements versus temperature T , and magnetization versus field M(H ) isotherm measurements. SrMn 2 Sb 2 adopts the trigonal CaAl 2 Si 2 -type structure, whereas BaMn 2 Sb 2 crystallizes in the tetragonal ThCr 2 Si 2 -type structure. The ρ(T ) data indicate semiconducting behaviors for both compounds with activation energies of 0.35 eV for SrMn 2 Sb 2 and 0.16 eV for BaMn 2 Sb 2 . The χ (T ) and C p (T ) data reveal antiferromagnetic (AFM) ordering at T N = 110 K for SrMn 2 Sb 2 and 450 K for BaMn 2 Sb 2 . The anisotropic χ (T T N ) data also show that the ordered moments in SrMn 2 Sb 2 are aligned in the hexagonal ab plane, whereas the ordered moments in BaMn 2 Sb 2 are aligned collinearly along the tetragonal c axis. The ab-plane M(H ) data for SrMn 2 Sb 2 exhibit a continuous metamagnetic transition at low fields 0 < H 1 T, whereas BaMn 2 Sb 2 exhibits no metamagnetic transitions up to 5.5 T. The χ (T ) and C p (T ) data for both SrMn 2 Sb 2 and BaMn 2 Sb 2 indicate strong dynamic short-range AFM correlations above their respective T N up to at least 900 K within a local-moment picture, corresponding to quasi-two...

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“…We also used our existing data on BaCo 2 As 2 , reported elsewhere [2,11] and other data from the literature. The 75 As NMR shift and spin-lattice relaxation rates 1/T 1 were measured under magnetic fields parallel to the c axis (H c) and to the ab plane (H ab).…”

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Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR

et al. 2015

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In the iron pnictide superconductors, theoretical calculations have consistently shown enhancements of the static magnetic susceptibility at both the stripe-type antiferromagnetic (AFM) and in-plane ferromagnetic (FM) wavevectors. However, the possible existence of FM fluctuations has not yet been examined from a microscopic point of view. Here, using 75 As NMR data, we provide clear evidence for the existence of FM spin correlations in both the hole-and electron-doped BaFe2As2 families of iron-pnictide superconductors. These FM fluctuations appear to compete with superconductivity and are thus a crucial ingredient to understanding the variability of Tc and the shape of the superconducting dome in these and other iron-pnictide families.PACS numbers: 74.70. Xa, 75.40.Gb The role of magnetic fluctuations in iron pnictide superconductors (SCs) has been extensively studied since their discovery. As the parent materials have antiferromagnetic (AFM) ground states, attention has been understandably focused on stripe-type AFM fluctuations, which are widely believed to give rise to the Cooper pairing in these systems. In the standard picture, carrier doping or pressure application results in suppression of the AFM order and the emergence of a SC state, with T c ranging from a few K to 56 K [1]. However, as of yet, there is no accepted theory for T c in these materials with which to explain the large variability in maximum T c between different iron arsenide families and the different shapes of the SC dome with electron and hole doping.Recent nuclear magnetic resonance (NMR) measurements on non-SC, paramagnetic (PM) SrCo 2 As 2 , the x = 1 member of the electron-doped Sr(Fe 1−x Co x ) 2 As 2 family, revealed strong ferromagnetic (FM) spin fluctuations in the Co layer coexisting with stripe-type AFM fluctuations [2,3]. Since stripe-type AFM fluctuations are a key ingredient to SC in the iron pnictides, this result suggested that FM fluctuations might compete with the stripe-type AFM fluctuations, suppressing SC in SrCo 2 As 2 . FM correlations were also observed in isostructural BaCo 2 As 2 [2, 4]. Similarly, CaCo 1.86 As 2 has an A-type AFM ground state with inplane FM order [5]. These results also raise the question of whether similar FM correlations exist generally in the SC A(Fe 1−x Co x ) 2 As 2 compounds, not just at the x = 1 edges of their phase diagrams.According to density functional theory calculations [6-10], the generalized static magnetic susceptibility χ(q) is enhanced at both the FM and stripe-type AFM wavevectors in all the iron-based SCs and parent compounds. Experimentally, the uniform χ(q = 0) of the parent compounds is enhanced by a factor of order five over band structure values, which is consistent with FM correlations [1]. Nevertheless, FM fluctuations have not been investigated microscopically, perhaps because low-energy FM fluctuations are difficult to observe via inelastic neutron scattering (INS). The peak in the inelastic structure factor at q = 0 coincides with the elastic Bragg diffractio...

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Crystallography and physical properties ofBaCo2As2,Ba0.94K0.06

Abstract: Crystallography and Physical Properties of BaCo 2 As 2 , Ba 0.94 K 0.06 Co 2 As 2 and Ba 0.78 K 0.22 Co 2 As 2

Cited by 39 publications

References 69 publications

Coexistence of antiferromagnetic and ferromagnetic spin correlations inSrCo2As2revealed byCo59and<

Coexistence of antiferromagnetic and ferromagnetic spin correlations inSrCo2As2revealed byCo59and<

Antiferromagnetism in semiconductingSrMn2Sb2andBaMn2Sb2single crystals

Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR

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