Publication: Local disorder and structure relation induced by magnetic exchange interactions in A_2(Mo_(1-y)Mn_y)_2O_7 pyrochlores
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2021-06-05
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Elsevier Science SA
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Abstract
We present an extended X-ray absorption fine structure study at the Mo K-edge of A_2(Mo_(1-y)Mn_y)_2O_7 (A = Gd, Ho; y = 0.05 and 0.10) pyrochlores, as a function of temperature and composition, coupled to diffractometric and magnetic characterizations. Extending the study reported in our previous paper on the pristine A_2Mo_2O_7 compounds to these Mo/Mn partially substituted samples, where we hypothesize a competition between double-exchange and superexchange couplings, we aim to check which structure parameters are related to the nature of the nearest-neighbor magnetic interactions, looking for the presence and evolution of order and structure anomalies. Two Ho samples A_2(Mo_(1-y)Mn_y)_2O_7 (y = 0.05 and 0.10) keep the spin-glass nature of the parent compositions with a strong distortion of the MoO octahedron and of the Mo - Ho and Mo - Mo second shell. On the other hand, two Gd_2(Mo_(1-y)Mn_y)_2O_7 samples, ferromagnetic at low temperature in the undoped case, show the appearance on a local scale of a spin-glass transition mirrored by a quite high structure disorder and by a distortion coherent with a lattice frustration after Mn-doping. Therefore, the Gd and Ho Mn-doped samples display a similar frustrated behavior, differently from the corresponding undoped ones.
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©2021 Elsevier Science
We gratefully acknowledge the Spanish CRG at the ESRF for providing beamtime under experiment HC-3343. MS thanks Prof. Monica Dapiaggi for useful discussions. GL thanks Prof. Fabio M. Canepa for illuminating discussions. F.R.-M. gratefully acknowledge the support of the AEI (Spanish Government) Project (No. MAT2017-86450-C4-1-R). F.R.-M. is indebted to MINECO for the "Ramon y Cajal" contract (Ref: RyC-2015-18626), which is co-financed by the European Social Fund.