Abnormal enhancement of ferromagnetism for LaMnO3+δ thin films with decreasing oxygen pressure

A M Zhang,X S Wu,J G Lin,W C Zhang

doi:10.1063/1.4978657

A M Zhang, X S Wu + Show 2 more

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https://doi.org/10.1063/1.4978657

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Abstract

The compressive LaMnO3+δ thin films with thickness of ∼20 nm are grown on LaAlO3 (001) single crystal substrates under various oxygen environment. With decreasing oxygen pressure, the in-plane compressive strain is enhanced. It is found that the breathing mode (Q1) and the basal plane distortion mode (Q2) of MnO6 octahedron are suppressed, while the octahedral stretching mode (Q3) is promoted. The promoted Q3 switches the orbital order from x2-1/y2-1 to (x2-y2)+(z2-1) type. The ferromagnetic (FM) transition temperature Tc increases from 85 K to 105 K and the low-temperature magnetization increases greatly by 175%. The abnormal enhancement of magnetization with decreasing oxygen pressure is ascribed to the strain enlarged FM domains due to the decreased MnO6 distortion and the switched orbital ordering. This result is advantageous to explain the novel phenomena in LaMnO3-related systems.

Highlights

With the technical advancement in growing the complexed oxide films, many novel phenomena such as two dimensional quantum gases,[1] superconductivity,[2] insulator-to-metal transition,[3] antiferromagnetic to ferromagnetic transition,[4] giant magnetoresistance,[5] and exchange bias,[6] are reported in perovskite oxide heterostructures
The in-plane constants of the films are performed by grazing X-ray diffraction (GIXRD) on Beamline 1W1A of Beijing Synchrotron Radiation Facility (BSRF)
It is worthy to note the field cooled (FC) magnetization at 5K increases from 64 to[176] emu/cm[3] (175%). These results indicate the ferromagnetic ordering is promoted by lowering oxygen pressure

Summary

INTRODUCTION

With the technical advancement in growing the complexed oxide films, many novel phenomena such as two dimensional quantum gases,[1] superconductivity,[2] insulator-to-metal transition,[3] antiferromagnetic to ferromagnetic transition,[4] giant magnetoresistance,[5] and exchange bias,[6] are reported in perovskite oxide heterostructures. The exchange-bias effect in LaNiO3/LaMnO3,8 the tunable ferroelectricity in non-ferroic NdMnO3/SrMnO3/LaMnO3,9 the metal-insulator transition in (LaMnO3)2n/(SrMnO3)n superlattices[10] and an enhanced Neel temperature in (LaMnO3)n/(SrMnO3)2n (n = 1, 2).[11] LMO crystallizes in orthorhombic structure with a space group of Pbnm at low temperature. It is a Mott-Hubbard A-type antiferromagnetic (AAFM) insulator with. The results of magnetic and optical properties are systematically analyzed by considering the orbital ordering and JT distortion in these stained films

EXPERIMENTAL DETAILS

RESULTS AND DISCUSSIONS

CONCLUSIONS