Abstract
We report the investigation of the Ni for Fe substitution in Fe4Nb2O9 by X-ray techniques (diffraction and absorption spectroscopy), transmission electron microscopy (TEM), magnetometry and magneto (di)electric measurements. Up to x = 1 in Fe4-xNixNb2O9, the structure remains trigonal, with a unit cell volume which decreases by −1.4% from x = 0 to 1, in accordance with the difference in the ionic radius of divalent iron and nickel whose oxidation states were obtained by XAS. Furthermore, EDX analyses and high resolution TEM confirm the homogeneous atomic distribution. The antiferromagnetic transition temperature TN = 75 K of Fe3NiNb2O9 (x = 1) is 18 K lower than that of Fe4Nb2O9. The magnetic field (H) dependence of the magnetization (M) of Fe3NiNb2O9 below TN exhibits a spin-flop like at about 1T, and a more ferromagnetic-like M(H) behaviour than that of Fe4Nb2O9. Similarly, below TN, the H-dependent electric polarization (P) for the x = 0.5 and 1 samples is steeper than the P(H) curve of the x = 0 compound. This points towards the key role of such chemical substitutions to induce larger magnetoelectric coefficient.
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