Stabilization and functional properties of La3NiAlMnO9 and La3CoAlMnO9 magnetoelectric triple perovskites

Abstract

Ferromagnetic La 3 NiAlMnO 9 (LNAMO) and La 3 CoAlMnO 9 (LCAMO) tripleperovskite thin films are stabilized in the 750-860 o C temperature range in 100 to 900 mTorr O 2 pressure range using pulsed-laser deposition. The LCAMO and LNAMO films exhibit ferromagnetism up to 190 K and 130 K respectively. The structural, optical and magnetic properties of these films demonstrate that the B-site 3d-cations, Al, Mn and Co or Ni ions, are structurally short-range ordered. The strong spin-lattice-polarization coupling in LCAMO is evidenced by the temperature dependence of the dielectric constant and the softening of the phonon frequencies starting in the vicinity of the ferromagnetic-to-paramagnetic phase transition mimicking the behaviours of La 2 CoMnO 6 double perovskite.

Phase formation, phonon behavior, and magnetic properties of novel ferromagnetic La3BAlMnO9 (B=Co or Ni) triple perovskites

“…3b). As pointed out earlier in the self-ordered LCMO phase 3 , this magnetodielectric response reaches a peak in the vicinity of the ferromagneticparamagnetic transition due to a γP 2 M 2 term in the Landau free energy equation as a consequence of the coupling between the polar and magnetic order parameters 3,12,13 . The observation of a magnetodielectric effect in these films illustrates the presence of a spinpolar coupling in LCAMO.…”

“…In order to study the spin-polar coupling in LCAMO, we measured the temperature dependence of the dielectric constant in LCAMO films grown on Nb:SrTiO 3 (001) under identical conditions 3,13 . Dielectric measurements were carried out at 10 kHz using a 1V-AC excitation under different values of applied magnetic field (viz., 0, 0.5, 10, 30 kOe) using a set-up described elsewhere 3 .…”

“…The epitaxial nature and the crystalline quality of the LCAMO and LNAMO films 13 were examined by X-ray diffractometer, operated in the θ-2θ and rocking curve modes using Cu-Kα radiation. XRD data were collected in the 2θ range of 15-60 o in a step of 0.01 o .…”

“…The epitaxial thin films of LCAMO and LNAMO on SrTiO 3 (001) were grown by ablating a stoichiometric target using a KrF excimer laser (λ = 248 nm) at 6Hz 13 . A growth temperature range of 720 to 860 o C in an O 2 pressure from 100 to 1000 mTorr was explored.…”

“…This unique system may be viewed as the alternating blocks of LaCoO 3 , 13 . It is also here important to note that the ionic radius of Al 3+ is very close to the value of Mn, Co, and/or Ni in an octahedral coordination.…”