Effect of cation disorder on structural, magnetic and dielectric properties of La₂MnCoO₆double perovskite

Abstract

The origin of dielectric anomalies and magnetodielectric response of La2MnCoO6 has been investigated by means of ultra-high resolution synchrotron x-ray powder diffraction, neutron powder diffraction, resistivity, magnetization and dielectric measurements. The study has been performed on two different bulk samples presenting different degrees of Mn/Co order: 95 and 74%. Beside the well-known influence on magnetic properties, our results show that the main effect of disorder lies on the electrical resistivity. Bond distances clearly show Mn4+/Co2+ valence states in the well-ordered sample, while for the disordered one this picture still holds. AC resistivity data show dielectric anomalies and a small magnetodielectric effect, but impedance complex plane analyses prove that these phenomena appear at the frequency–temperature region where extrinsic effects dominate the dielectric response.

Spin reorientation and disordered rare earth magnetism in Ho2FeCoO6

“…Hence, our first attempt was to refine the diffraction data in the cation-ordered P 2 1 /n space group. However, if the cations are ordered in the double perovskite structure, it leads to the appearance of (011) peak in the diffracted intensity [39]. The absence of such a peak in the neutron diffraction data of Ho 2 FeCoO 6 suggested that the degree of ordering is very low in this compound.…”

Intrinsic dielectric properties of magnetodielectric La2CoMnO6

“…Structural investigations by neutron diffraction has shown that these compounds crystallize into a monoclinic structure with charge ordering of rock salt type (A 2 BB'O 6 ), belonging to the , (#14 or ) 11,12 space group. Within this structure, the cationic ordering state of the B e B' ions, occupying respectively the 2c e 2d Wyckoff sites, has a strong influence on the vibrational, electrical and magnetic properties of the material.…”

“…Within this structure, the cationic ordering state of the B e B' ions, occupying respectively the 2c e 2d Wyckoff sites, has a strong influence on the vibrational, electrical and magnetic properties of the material. In particular, the ordering of the magnetic ions (Mn, Co or Ni) in B/B' sites affects the spinphonon coupling 13,14 , the critical magnetic temperatures 15 , the electrical conductivity 12,16 and the dielectric constant 17,18 . Concerning the dielectric constant of LCMO there are some discrepancies on the results presented in the literature: Yáñez-Vilar et al 18 reported that the radio-frequency (<10 4 Hz) dielectric constant of their ceramic samples, at room temperature, increased by two orders of magnitude from the ordered to disordered material, attaining values as high as 10 5 .…”

“…By increasing the frequency (10 6 Hz) and lowering the temperature (100 K), the dielectric constant decreases to ' 15, for the ordered and ' 30, for the disordered samples. Barón-González et al 12 , on the same external conditions (10 6 Infrared spectroscopy is an ideal tool for solving controversies concerning intrinsic or extrinsic nature of the dielectric response of an insulator (and/or high-gap semiconductor) material, because for very low charged defects concentration, the infrared dielectric response (10 11 -10 14 Hz) is completely determined from the phononic and electronic polarizations, i.e., is purely of intrinsic origin. Therefore, this technique would be very helpful for investigating the dielectric behavior of LCMO and discuss its CDC effect.…”

Engineering the microstructure and magnetism of La2CoMnO6−δ thin films by tailoring oxygen stoichiometry

“…In situ annealing conditions allow tailoring the oxygen content of the films, therefore controlling their microstructure and magnetic properties. PACS: 75.70.Ak, 81.15.Cd 4 Bulk La 2 CoMnO 6 (LCMO) double perovskite has been the subject of strong interest during the last years [ 1,2,3,4,5,6,7] due to its ferromagnetic insulating character.Besides its perspectives as magnetodielectric material, LCMO is a good candidate for active insulating barriers in spin filters. For these devices, insulating barriers must be thin enough to enable tunneling conduction.…”