Mössbauer Study of the Direction of Spin Alignment in Oxalate-Bridged Metal Assemblies

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Abstract
The direction of spin alignment was investigated for three mixed crystal systems of molecule-based magnets, NBu4[Fe(II) x Mn(II)1−x Cr(III)(ox)3] (x = 0.03−1), NBu4 [Mn(II)Fe(III) x Cr(III)1− x(ox)3] (x = 0.04–1) and NBu4[Fe(II) x Ni(II)1− xFe(III)(ox)3] (x = 0 − 1), by using 57Fe Mössbauer spectroscopy, where NBu4 ± = tetra(n-butyl)ammonium ion and ox2− = oxalate ion. With the decrease of x, the direction of the internal magnetic field (H n) at Fe(II) nucleus in NBu4[Fe(II) x Mn(II)1−x Cr(III) (ox)3] was changed gradually from parallel to perpendicular, to the honeycomb layers consisting of an alternate array of the bivalent and tervalent ions through ox2− ligands; this indicates that the Mn(II) spin direction in NBu4[Mn(II)Cr(III)(ox)3] (x = 0) is almost perpendicular to the honeycomb layers. An approximately perpendicular spin alignment was also indicated for the Cr(III) ions in the same compound, from the x-dependence of the Fe(III) spin direction in NBu4[Mn(II)Fe(III) x Cr(III)1−x (ox)3]. A variation of ca. 50° in direction was observed for the H n at Fe(III) in NBu4[Fe(II) x Ni(II)1−x Fe(III)(ox)3].

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