E. Legarra

Fluorinated mixed valence Fe(II)–Fe(III) phosphites with channels templated by linear tetramine chains. Structural and magnetic implications of partial replacement of Fe(II) by Co(II)

Three new fluorinated mixed valence Fe(II)–Fe(III) phosphites were synthesized by employing mild hydrothermal conditions. (H4baepn)0.5[FeIII2.3FeII1.7(H2O)2(HPO3)4−(x+y)(HPO4)x(PO4)yF4] (x ≃ 0.13, y ≃ 0.3) (1) (baepn = N,N′-bis(2-aminoethyl)-1,3-propanediamine (C7N4H20)) and the Co(II)-substituted phase with the formula (H4baepn)0.5[FeIII2.0FeII0.71CoII1.29(H2O)2(HPO3)4−x(HPO4)xF4] (x ≃ 0.38) (2) were studied by single crystal X-ray diffraction. The phase with the major content of Co(II), (H4baepn)0.5[FeIII2.0FeII0.62CoII1.38(H2O)2(HPO3)4−x(HPO4)xF4] (x ≃ 0.38) (3) was obtained as a polycrystalline powder and studied by Rietveld refinement by using the structural model of 2. These compounds were characterized by ICP-Q-MS, thermogravimetric and thermodiffractometric analyses, and XPS, IR, UV/vis and Mossbauer spectroscopy. The single crystal data indicate that phases 1 and 2 crystallize in the P21/c space group with lattice parameters a = 13.6808(4), b = 12.6340(2), c = 12.7830(3) A and β = 116.983(4)° for 1 and a = 13.6823(4), b = 12.6063(3), c = 12.7535(4) A and β = 116.988(4)° for 2, with Z = 4. The reciprocal space of 1 shows satellite reflections with a modulation wavevector q = 0.284(2)a* which indicate an incommensurate long-range order. The average structure of these compounds is built up by a 3D lattice constructed by inorganic layers of Fe(III) chains and Fe(II) and Co(II) dimers joined by phosphite groups partially substituted by HPO4 and PO4 tetrahedral groups. These anionic layers stack along the [100] direction encapsulating linear tetramines in eight-membered open channels involving host–guest interactions. Magnetic measurements of 1 and 3 showed antiferromagnetic coupling as the major interactions, exhibiting a weak ferromagnetic component together with a spin glass transition at low temperature in the case of 1. Heat capacity measurements showed a small anomaly at 20.5 K for 1 and a sharp magnetic peak at 28 K for 3. Unexpectedly, the small anomaly observed in 1 increased with the magnetic field and became better defined.

Fe-Al Alloys' Magnetism

F. Plazaola1, E. Apinaniz3, D. Martin Rodriguez4, E. Legarra1 and J. S. Garitaonandia2 1Elektrika eta Elektronika Saila, Euskal Herriko Unibertsitatea UPV/EHU, Bilbao, 2Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea UPV/EHU, Bilbao, 3Fisika Aplikatua I Saila, Euskal Herriko Unibertsitatea UPV/EHU, Bilbao, 4Julich Centre for Neutron Science and Institute for Complex Systems, Forschungszentrum Julich GmbH, Julich, 1,2,3Spain 4Germany

Mösbauer spectroscopy study of the influence of Si addition to ordered and disordered Fe60Al40 alloys

We have used Mossbauer spectroscopy to study the influence of Si addition to Fe60Al40 composition without changing the iron content of the alloy. The study has been performed in ordered and mechanically deformed samples. This work shows that the B2 structure present in ordered Fe60Al40 alloy does not change with Si introduction in the studied ternary alloys. However, the binary Fe60Si40 alloy shows D03 and B20 structures. Mechanical deformation of the ordered samples induces a clear change of the Mossbauer spectra of binary alloys with the presence of new sextets or variation of the previous ones; however, the Mossbauer spectra of the studied ternary alloys are very similar to the ordered ones.