Raman spectroscopy evidence of strong spin-phonon coupling in epitaxial thin films of the double perovskite La2NiMnO6

Abstract

The Raman spectra of epitaxial thin films of La2NiMnO6 on (001)-oriented LaAlO3 substrates have been measured in several exact scattering configurations between 12 and 773K. The evolution of the spectra with increasing temperature is consistent with a transition from the monoclinic P121∕n1 to rhombohedral R3¯ structure. The spin-phonon coupling results in significant softening of the phonon mode involving stretching vibrations of the (Ni∕Mn)O6 octahedra. The anomalous softening extends above TC=275K, indicating the presence of short range ordering up to 400K.

Multiferroic double perovskites: Opportunities, issues, and challenges

“…On the contrary, the admixture films display two magnetic transitions (at 295 K and 140 K) illustrating that these films have both ordered and disordered domains. The magnetic interactions in LNMO are governed by the 180 osuperexchange process 5 arising from the bond between oxygen and the partially-filled Ni In the magnetic insulators, the spin-phonon coupling arises from the phonon modulation of the superexchange integral which is ultimately governed by the amplitude of the spin-spin correlation <S i .S j > functions where S i and S j are the localized spins at the i th and j th sites, respectively 17 . Within the mean-field framework, the phonon renormalization function δω (T) 17 …”

“…The crystallinity and the epitaxial quality of the LNMO films were studied using Polarized Raman scattering is a stringent measurement to illustrate the B'/B'' cation ordering in double perovskites and has indeed been successfully used to identify local ordering, structural distortions, and spin-phonon coupling 17,19 . We measured the temperature dependence of the Raman spectra of our disordered, ordered and admixture films in the XX, X'X', XY, X'Y' polarization configurations 19 .…”

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

“…Our studies further suggest that a growth temperature above 860 o C (an accessibility limit to our PLD system) may be required to obtain long range ordered LCAMO triple perovskites. Polarized Raman scattering is a powerful technique to study local structures and spin-phonon coupling in magnetic oxides 6,10,11 . It has been successfully used to demonstrate the presence of strong spin-phonon coupling in LNMO and LCMO films 6,10,11 .…”

“…This illustrates the presence of a strong spin-polar coupling effect in these systems [1][2][3] and the possibility of their potential uses in real spintronic devices. Within the Landau Free energy framework, this MD effect 3 is explained by a γP 2 M 2 coupling term, wherein γ is the coupling constant, P is the electrical polarization, and M is the magnetization order parameters 6,10,11 .…”

“…These systems show a ferromagnetic insulator 8 behavior and a strong spin-phononpolar coupling [1][2][3][4][5][6][9][10][11][12] . In these systems, ferromagnetism with an insulator characteristic arises due to the 180 o superexchange interaction between B-O-Mn cations, as described by Goodenough and Kanamori 8 .…”