A variable temperature EPR study of the manganites (La1/3Sm 2/3)2/3SrxBa0.33-xMnO3 (x=0.0, 0.1, 0.2, 0.33): Small polaron hopping conductivity and Griffiths phase

Misra, S K and Andronenko, S I and Asthana, Saket and Bahadur, D (2010) A variable temperature EPR study of the manganites (La1/3Sm 2/3)2/3SrxBa0.33-xMnO3 (x=0.0, 0.1, 0.2, 0.33): Small polaron hopping conductivity and Griffiths phase. Journal of Magnetism and Magnetic Materials, 322 (19). pp. 2902-2907. ISSN 0304-8853

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Abstract

Four manganite samples of the series, (La1/3Sm 2/3)2/3SrxBa0.33-xMnO3, with x=0.0, 0.1, 0.2 and 0.33, were investigated by X-band (∼9.5 GHz) electron paramagnetic resonance (EPR) in the temperature range 4300 K. The temperature dependences of EPR lines and linewidths of the samples with x=0.0, 0.1 and 0.2, containing Ba2 ions, exhibit similar behavior, all characterized by the transition temperatures (TC) to ferromagnetic states in the 110150 K range. However, the sample with x=0.33 (containing no Ba2 ions) is characterized by a much higher TC=205 K. This is due to significant structural changes effected by the substitution of Ba2 ions by Sr2 ions. There is an evidence of exchange narrowing of EPR lines near Tmin, where the linewidth exhibits the minimum. Further, a correlation between the temperature dependence of the EPR linewidth and conductivity is observed in all samples, ascribed to the influence of small-polaron hopping conductivity in the paramagnetic state. The peak-to-peak EPR linewidth was fitted to ΔBpp(T)=ΔB pp,minA/Texp(-Ea/kBT), with Ea=0.09 eV for x=0.0, 0.1 and 0.2 and Ea=0.25 eV for x=0.33. From the published resistivity data, fitted here to σ(T)∝1/T exp(-E σ/kBT), the value of Eσ, the activation energy, was found to be Eσ=0.18 eV for samples with x=0.0, 0.1 and 0.2 and Eσ=0.25 eV for the sample with x=0.33. The differences in the values of Ea and Eσ in the samples with x= 0.0, 0.1and 0.2 and x=0.33 has been ascribed to the differences in the flip-flop and spin-hopping rates. The presence of Griffiths phase for the samples with x=0.1 and 0.2 is indicated; it is characterized by coexistence of ferromagnetic nanostructures (ferrons) and paramagnetic phase, attributed to electronic phase separation.

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IITH Creators:
IITH CreatorsORCiD
Asthana, Sakethttp://orcid.org/0000-0002-6420-3304
Item Type: Article
Uncontrolled Keywords: Doped manganites; Electron paramagnetic resonance; Electronic phase separation; EPR studies; Ferromagnetic nanostructures; Ferromagnetic state; Ferrons; Griffiths phase; Higher T; Hopping rate; Paramagnetic phase; Paramagnetic state; Polaron hopping; Polaron hopping conductivity; Resistivity data; Small polaron hopping; Structural change; Temperature dependence; Temperature range; Transition temperature; Variable temperature; Doped manganites; Electron paramagnetic resonance (EPR); Griffiths phase; Small-polaron hopping
Subjects: Physics > Magnetism
Divisions: Department of Physics
Depositing User: Mr. Siva Shankar K
Date Deposited: 13 Oct 2014 04:36
Last Modified: 29 Aug 2017 10:01
URI: http://raiith.iith.ac.in/id/eprint/203
Publisher URL: https://doi.org/10.1016/j.jmmm.2010.05.003
OA policy: http://www.sherpa.ac.uk/romeo/issn/0304-8853/
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