Ferromagnetic clusters in the Brownmillerite bilayered compounds Ca2.5−xLaxSr0.5GaMn2O8: An approach to achieve layered spintronics materials

Abstract

We report the effect of La-substitution on the magnetic and magnetotransport properties of Brownmillerite-like bilayered compounds Ca 2.5-x La x Sr 0.5 GaMn 2 O 8 (x = 0, 0.05, 0.075, and 0.1) by using dc-magnetization, resistivity and magnetoresistance techniques. The Rietveld analysis of the room temperature x-ray diffraction patterns confirms no observable change of average crystal structure with the La-substitution. Both magnetic and magnetotransport properties are found to be very sensitive to the La-substitution. Interestingly, the La-substituted compounds show ferromagnetic-like behavior (due to the occurrence of a double exchange mechanism) whereas, the parent compound is an antiferromagnet (T N~1 50 K). All compounds show an insulating behavior, in the measured temperature range of 100 -300 K, with an overall decrease in the resistivity with the substitution. A higher value of magnetoresistance has been successfully achieved by the La-substitution. We have proposed an electronic phase separation model, considering the formation of ferromagnetic clusters in the antiferromagnetic matrix, to interpret the observed magnetization and magnetotransport results for the La-substituted samples. The present study demonstrates an approach to achieve new functional materials, based on naturally occurring layered system like Ca 2.5-x La x Sr 0.5 GaMn 2 O 8 , for possible spintronics applications.

Effect of electron doping on the magnetic correlations in the bilayered brownmillerite compound Ca2.5−xLaxSr0.5GaMn2O8: a neutron diffraction study

“…As a result, a ferromagnetic-like magnetic behaviour with enhanced magnetoresistance has been observed [17]. These properties make this type of naturally grown layered systems suitable for spintronics applications.…”

“…Therefore, a decrease of T N is evident with the La substitution. Here, we would like to mention that our previous study using magnetization and magnetoresistance showed the appearance of FM interactions due to double exchange (DE) mechanism with electron doping or La substitution [17]. A competition between the leading superexchange (SE) AFM and the electron doping induced double exchange (DE) FM interactions may cause a decrease in the average SE AFM exchange interaction, resulting to the observed decrease of the T N value.…”

“…Our previous crystal structural study based on room temperature X-ray diffraction suggested that there was no observable change in the average crystal structure with La substitution [17]. However, an enhancement in the local Jahn-Teller distortion may be expected due to the increase of the concentration of Mn 3+ ion with La-substitution.…”

“…The polycrystalline samples of Ca 2.5-x La x Sr 0.5 GaMn 2 O 8 (x = 0.05 and 0.1) were prepared by the solid state reaction method as described in our previous report [17]. Neutron powder diffraction measurements were carried out over the temperature range of 4. agreement with the previously reported values, obtained from an independent X-ray diffraction study [17].…”

“…The diffraction patterns at 275 K could be fitted with only nuclear intensities confirming the paramagnetic nature of the samples at this temperature. The fractional atomic positions were taken from our earlier X-ray diffraction study [17], and kept fixed during refinement. This method was can be decomposed as a direct sum of irreducible representations as…”