Raman evidence for presence of high-temperature ferromagnetic clusters in magnetodielectric compound Ba-doped
D A B Barbosa1, C W A Paschoal2
1Coordenação de Licenciatura em Ciências Naturais, Universidade Federal do Maranhão, Campus Bacabal, 65418-000 Bacabal, MA, Brazil; Departamento de Física, Universidade Federal do Maranhão, Campus do Bacanga, 65085-580 São Luis, MA, Brazil.
Abstract:
Magnetodielectric ferromagnetic semiconductors are key materials because of their applications in spintronic devices; they can be used to control the magnetic properties by applying electric fields. La2NiMnO6 emerged as an important magnetodielectric ferromagnetic semiconductor because of its high Curie temperature near room temperature. Recently Ba doped was successfully used to improve magnetic properties in La2NiMnO6, originating partially ordered systems with different ordering degrees but presenting same Tc=280K. However, the influence of Ba doping on the temperature dependent vibrational properties of the system was not investigated. To investigate the Ba doping influence on temperature dependent phonon spectra in La2NiMnO6, we used Raman Spectroscopy to probe the symmetric stretching mode behavior in the range from 10 to 600K. Remarkable softenings were detected in the phonon behavior due to spin phonon coupling, at several different temperatures, much above Tc. The FWHM dependence with temperature rules out magnetostriction effects. The phonon softenings are the largest reported so far for the RE2NiMnO6 systems and also indicate that Ba doping induces ordering in the Ni/Mn sites. The temperature discordance in characteristic softening onset of the spin phonon coupling are related to ferromagnetic short range clusters due the presence of Ni3+, Mn3+ oxidation states.
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