Selective Metal Exsolution in BaFe(2-y)M(y)(PO4)2 (M = Co(2+), Ni(2+)) Solid Solutions.
The 2D-Ising ferromagnetic phase BaFe(2+)2(PO4)2 shows exsolution of up to one-third of its iron content (giving BaFe(3+)1.33(PO4)2) under mild oxidation conditions, leading to nanosized Fe2O3 exsolved clusters. Here we have prepared BaFe(2-y)M(y)(PO4)2 (M = Co(2+), Ni(2+); 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 Fe(2+) to Fe(3+) leaves stable M(2+) ions, as verified by (57)Fe Mössbauer spectroscopy, TGA, TEM, microprobe, and XANES. The size of the nanometric α-Fe2O3 clusters 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 BaFe(0.5-x)Co(1.5)(PO4)2) was detected even at 78 K. Although Ni(2+) and Co(2+) ions tend to block Fe diffusion, the crystal structure of BaFe(0.67)Co1(PO4)2 demonstrates a fully ordered rearrangement of Fe(3+) and Co(2+) ions after Fe exsolution. The magnetic behaviors of the Fe-depleted materials are mostly dominated by antiferromagnetic exchange, while Co(2+)-rich compounds show metamagnetic transitions reminiscent of the BaCo2(PO4)2 soft helicoidal magnet.
Université Lille Nord de France , UCCS, UMR-CNRS 8181, ENSCL-USTL, 59652 Villeneuve d'Ascq, France.
Ignacio
I
Blazquez Alcover
Université Lille Nord de France , UCCS, UMR-CNRS 8181, ENSCL-USTL, 59652 Villeneuve d'Ascq, France.
Sylvie
S
Daviero-Minaud
Universite Picardié Jules Verne , Laboratoire de Réactivité et Chimie des Solides, UMR 7314, 33 rue Saint Leu,80039 Amiens Cedex, France.
Rénald
R
David
Department of Chemistry, Moscow State University , 119991 Moscow, Russia.
Dmitry
D
Filimonov
Université Lille Nord de France , UCCS, UMR-CNRS 8181, ENSCL-USTL, 59652 Villeneuve d'Ascq, France.
Marielle
M
Huvé
School of Chemistry and Centre for Science at Extreme Conditions, University of Edinburgh , Edinburgh EH9 3JZ, U.K.
J Paul
JP
Attfield
Université Lille Nord de France , UCCS, UMR-CNRS 8181, ENSCL-USTL, 59652 Villeneuve d'Ascq, France.
Houria
H
Kabbour
Université Lille Nord de France , UCCS, UMR-CNRS 8181, ENSCL-USTL, 59652 Villeneuve d'Ascq, France.
Olivier
O
Mentré