Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric

•Short-range magnetic correlations can enhance thermoelectric performance•Neutron scattering yields a detailed view of 3D in MnTe•Spatially anisotropic antiferromagnetic survive at high temperature•First-principles calculations reproduce the short-range Thermoelectric materials hold tremendous promise for energy applications, but developing economically and environmentally viable high-performance thermoelectrics remains challenging. Recently, paramagnon drag effect was discovered, which local thermal fluctuations magnetization known as paramagnons charge carriers impart to them contribution thermopower. This is significant because it opens new avenue optimizing properties semiconductors. In this work, neutron used visualize nanoscale magnetism responsible semiconductor MnTe. First-principles quantitatively observed above ordering temperature. These results shed light on how enhances thermoelectricity provide template studies other semiconductors potential thermoelectrics. Short-range significantly increase thermopower semiconductors, representing noteworthy development decades-long effort develop materials. Here, we reveal nature thermopower-enhancing Using pair distribution function analysis neutron-scattering data, obtain detailed, real-space robust, nanometer-scale, that persist into paramagnetic phase Néel temperature TN = 307 K. The correlation length state longer along crystallographic c axis than within ab plane, pointing interactions. Ab initio spin-spin using density functional theory disordered moment approach result with quantitative accuracy. findings constitute first picture spin magnetically enhanced inform future efforts optimize performance by means. Despite devices friendly applications ranging from waste heat recovery solid-state refrigeration,9Gaultois M.W. Sparks T.D. Borg C.K.H. Seshadri R. Bonificio W.D. Clarke D.R. Data-driven review materials: resource considerations.Chem. 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Moving vertically up down pattern, observe alternating dark bright regions indicative c, while exhibits rows uniform color, plane. qualitatively similar those ordered state. Interestingly, reveals striking anisotropy length, z clearly visible about ±30 Å, x shorter spatial extent. quantified taking cuts displayed 0 lines fitting exponential envelope profile, Figures 1B 1C. procedure lengths 7.7(4) 4.3(2) respectively. note pattern collected without any discrimination instrument should therefore considered totally integrated pattern,27Fry-Petit A.M. Rebola Mourigal Valentine Drichko Sheckelton J.P. Fennie C.J. McQueen T.M. Direct assignment molecular vibrations normal mode dynamic technique.J. 143: 124201Crossref probes instantaneous correlations. just neutrons scattered elastic bandwidth ?2 meV selected (hence providing sensitivity lifetime ps), out-of-plane in-plane 14.8(9) 5.8(3) Additional details regarding provided S5–S7 accompanying discussion, including diffuse patterns simulated models Although reciprocal space contains same information does 3D-?mPDF, transforming space, visual inspection straightforward immediately salient further performed 1D atomic powder samples Na-doped dense grid across 2A shows fits together 100 pure upper set curves represent (blue symbols) calculated (red curve), includes best-fit signals together. published structures17Szuszkiewicz starting point refinement S3 full refinements). fit (Rw 0.0576), seen small featureless residual green curve bottom panel. best occurs when aligned Due symmetry, no preferred plane could detected, although Kriegner al.28Kriegner Výborný Olejník Reichlová Novák Marti Gazquez Saidl N?mec P. 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Qualitatively 500 K, highest measured locally extracted conducted ranges 1.5–20 30–45 Å supplemental information) 3B blue triangles orange circles, latter range abrupt onset well described continuous critical exponent ? 0.30 ± 0.03. contrast, indicate fraction bare among near neighbors least evolution reminiscent biased applied field,30Blundell Magnetism Condensed Matter. Oxford University Press, 2001Google suggesting field created neighboring plays field. Above TN, decay asymptotically approaches constant 1.1 ?B characteristic scale 90 solid curve. given S4 discussion. additional implemented model distinct (?c) (?ab). At temperatures ?c ?ab approximately 50% 3C), confirming demonstrating sufficient detecting spatially 3, show rapid decrease 350 they remain fairly 3B. determined 1D-mPDF Angstroms, smaller obtained Zheng al.15Zheng (2.5 nm). disparity partially ameliorated multiplying ? account definitions two works Dun al.31Dun Daum Baral Fischer H.E. 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Lindsay L. Phonons, 3: 025403Crossref (26) schematic showing interactions). J2 rationalized structural viewpoint context superexchange theory33Anderson P.W. Theory interactions: insulators semiconductors.Solid State 1963; 14: 99-214Crossref (945) noting distance ?3.36 Mn-Te-Mn pathway forms angle ?70° (favoring strong antiferromagnetism), ?4.15 ?90° ferromagnetism). possesses character somewhat interacting chains. J3 favors alignment third-nearest neighbors, which, combined action J1, contributes correlation. presence favorable ingredient paramagnon-enhanced thermopower,20Polash supported raises interesting possibility itself anisotropic. For effective, must exceed mobile electrons’ de Broglie wavelength (?dB) effective Bohr radius (a?), likewise electron-on-paramagnon time.15Zheng ratio time anisotropic, considering larger ratios ?dB a?,15Zheng may necessarily question answered direction-dependent MnTe, exist knowledge. Theoretical modeling issue. notable reasons. 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