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Selective Metal Exsolution in BaFe2-yMy(PO4)2 (M = Co2+, Ni2+) Solid Solutions

Journal Article · · Inorganic Chemistry
 [1];  [1];  [2];  [3];  [1];  [4];  [1];  [1]
  1. Universite Lille Nord de France (France)
  2. Universite Picardie Jules Verne (France)
  3. Moscow State Univ., Moscow (Russian Federation)
  4. Univ. of Edinburgh (United Kingdom)
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The 2D-Ising ferromagnetic phase BaFe2+2(PO4)2 shows exsolution of up to one-third of its iron content (giving BaFe3+1.33(PO4)2) under mild oxidation conditions, leading to nanosized Fe2O3 exsolved clusters. Here we have prepared BaFe2–yMy(PO4)2 (M = Co2+, Ni2+; y = 0, 0.5, 1, 1.5) solid solutions to investigate the feasibility and selectivity of metal exsolution in these mixed metallic systems. For all the compounds, after 600 °C thermal treatment in air, a complete oxidation of Fe2+ to Fe3+ leaves stable M2+ ions, as verified by 57Fe Mössbauer spectroscopy, TGA, TEM, microprobe, and XANES. Furthermore, the size of the nanometric α-Fe2O3clusters coating the main phase strongly depends on the yM metal concentration. For M-rich phases the iron diffusion is hampered so that a significant fraction of superparamagnetic α-Fe2O3 particles (100% for BaFe0.5–xCo1.5(PO4)2) was detected even at 78 K. Although Ni2+and Co2+ ions tend to block Fe diffusion, the crystal structure of BaFe0.67Co1(PO4)2demonstrates a fully ordered rearrangement of Fe3+ and Co2+ ions after Fe exsolution. We found that the magnetic behaviors of the Fe-depleted materials are mostly dominated by antiferromagnetic exchange, while Co2+-rich compounds show metamagnetic transitions reminiscent of the BaCo2(PO4)2 soft helicoidal magnet.
Research Organization:
Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC02-06CH11357
OSTI ID:
1225094
Journal Information:
Inorganic Chemistry, Journal Name: Inorganic Chemistry Journal Issue: 17 Vol. 54; ISSN 0020-1669
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
ENGLISH

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