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Abstract

We have studied the effect of replacing Mn³⁺ by Cr³⁺ on the structure, transport and magnetism in the bilayered manganite LaSr2Mn2O7. Although no structural transition was observed in LaSr2Mn2−yCryO7 (0.1≤y≤0.6), the electrical transport and the magnetic properties were found to be affected significantly by this substitution. Substitution of Cr³⁺ reduces the conductivity by restricting the hopping of small polarons. Magnetization increases with increasing Cr³⁺ concentration suggesting that Cr³⁺-ions induce ferromagnetic moments. The ferromagnetic and an antiferromagnetic phase observed above ∼60K merge into an inhomogeneous phase below this temperature. Thermopower yields an essentially concentration independent charge density nearly equal to its value for chromium free composition inspite of its expected decrease with this substitution suggesting that the small charge density of the insulating AFM phase is supplemented by the free carriers in the FM phase. The inhomogeneous phase shows a relaxor type behavior which contrasts with the spin glass behavior seen in La0.46Sr0.54Mn0.98Cr0.02O3 having an identical AFM magnetic state. The difference is attributed to the non-JT character of Cr-ions which reduce the distortion of the MnO octahedra located within the FM domains. With a higher lattice strain in the surrounding AFM matrix the carriers remain confined within the FM domains leading to the relaxor type behavior.

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Reentrant behavior in Cr doped bilayer manganite LaSr2Mn2O7

We have studied the effect of replacing Mn³⁺ by Cr³⁺ on the structure, transport and magnetism in the bilayered manganite LaSr2Mn2O7. Although no structural transition was observed in LaSr2Mn2−yCryO7 (0.1≤y≤0.6), the electrical transport and the magnetic properties were found to be affected significantly by this substitution. Substitution of Cr³⁺ reduces the conductivity by restricting the hopping of small polarons. Magnetization increases with increasing Cr³⁺ concentration suggesting that Cr³⁺-ions induce ferromagnetic moments. The ferromagnetic and an antiferromagnetic phase observed above ∼60K merge into an inhomogeneous phase below this temperature. Thermopower yields an essentially concentration independent charge density nearly equal to its value for chromium free composition inspite of its expected decrease with this substitution suggesting that the small charge density of the insulating AFM phase is supplemented by the free carriers in the FM phase. The inhomogeneous phase shows a relaxor type behavior which contrasts with the spin glass behavior seen in La0.46Sr0.54Mn0.98Cr0.02O3 having an identical AFM magnetic state. The difference is attributed to the non-JT character of Cr-ions which reduce the distortion of the MnO octahedra located within the FM domains. With a higher lattice strain in the surrounding AFM matrix the carriers remain confined within the FM domains leading to the relaxor type behavior.

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Keywords

fm domains small magnetism electrical transport magnetic properties antiferromagnetic phase italicferromagnetic lattice strain relaxor type behavior mnglyph namesbndo octahedra independent charge density bilayered manganite lasrinf locpost2infmninf ferromagnetic nonjt character locpost046infsrinf locpost054infmninf locpost098infcrinf locpost002infoinf locpost2infmninf locpost2yinfcrinf locpostyinfoinf locpost7inf 01hsp sp025hsp sp025yhsp sp025hsp spin glass behavior magnetization free composition crsup locpost3sup concentration crions

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Niharika Mohapatra,S.N. Bhatia,.Reentrant behavior in Cr doped bilayer manganite LaSr2Mn2O7. 434 (0),.

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