title: Spontaneous magnetization in Ni-Al and Ni-Fe layered double hydroxides.
abstract: Layered double hydroxides containing paramagnetic Ni (II) and diamagnetic/paramagnetic Al (III)/Fe (III) ions have been prepared and characterized. Ni 2Al(OH) 6(NO 3). nH 2O ( 1), Ni 2Fe(OH) 6(NO 3). nH 2O ( 2), Ni 2Fe(OH) 6(C 6H 8O 4) 0.5. nH 2O ( 3), and Ni 2Fe(OH) 6(C 10H 16O 4) 0.5. nH 2O ( 4) were prepared by coprecipitation at controlled pH as polycrystalline materials with the typical brucite-like structure, with alternating layers of hydroxide and the corresponding anions, which determine the interlayer separation. Magnetic studies show the appearance of spontaneous magnetization between 2 and 15 K for these compounds. Interestingly, the onset temperature for spontaneous magnetization follows a direct relationship with interlayer separation, since this is the only magnetic difference between compounds 2, 3, and 4. Magnetic and calorimetric data indicate that long-range magnetic ordering is not occurring in any of these materials, but rather a freezing of the magnetic system in 3D due to the magnetic disorder and competing intra- and interlayer interactions. Thus, these hydrotalcite-like magnetic materials can be regarded as spin glasses.
authors.affiliation: Instituto de Ciencia Molecular, Universidad de Valencia, Poligono de la Coma, s/n, 46980 Paterna, Spain.
authors.forename: Eugenio
authors.initials: E
authors.lastname: Coronado
authors.forename: José R
authors.initials: JR
authors.lastname: Galán-Mascarós
authors.forename: Carlos
authors.initials: C
authors.lastname: Martí-Gastaldo
authors.forename: Antonio
authors.initials: A
authors.lastname: Ribera
authors.forename: Elías
authors.initials: E
authors.lastname: Palacios
authors.forename: Miguel
authors.initials: M
authors.lastname: Castro
authors.forename: Ramón
authors.initials: R
authors.lastname: Burriel