| As a typical strong correlated electron system,mixed valence perovskite manganese oxide shows phase separation and exchange bias effect because of coupling among spin,electron,crystal lattice and orbit.Exchange bias,a shift of the hysteresis loop from the center position,is frequently observed in a ferromagnetic?FM?material coupled with an antiferromagnetic?AFM?material.To date,the exchange bias effect has been widely studied in different material system because of its application,such as magnetic read heads,nonvolatile memories,and various sensors.The two-layer perovskite manganese oxide Pr(Sr0.1Ca0.9)2Mn2O7 has been observed the phase separation due to charge/orbital order at low temperature,so the exchange bias effect will be influenced by the thickness and microstructure of the thin film materials.The Pr(Sr0.1Ca0.9)2Mn2O7 films have been synthesized on Pt/Ti/SiO2/Si substrate by pulsed laser deposition,and the exchange bias effect of these materials has been researched.The main research in the following two aspects:?1?The effect of thickness on exchange bias effect in PSCMO thin filmsDifferent thickness?72nm-940nm?two-layer perovskite manganese oxide Pr(Sr0.1Ca0.9)2Mn2O7 films have been synthesized on Pt/Ti/SiO2/Si substrate by pulsed laser deposition,and the surface morphology of the films shows uniform triangular grains by SEM.The exchange bias effect in different thickness films has been observed and first increases in the samples of 72nm-720 nm and then decrease in the samples of 720nm-940 nm with the increasing thickness.The exchange bias effect of 720 nm film is up to maximum.Magnetic phase analysis shows that the different ferromagnetic phases and antiferromagnetic phases in these films are the main reason for this phenomenon with the different thickness.The exchange bias effect increases with the increasing cooling field and the vertical and horizontal exchange bias are 1.36×10-4emu/cm2 and-160 Oe at the temperature of 5K and cooling field of 7000 Oe in the 720 nm thickness film.However,the exchange bias effect decreases with the increasing temperature in the fixed cooling field and disappears at 28 K.The temperature of 28 K is consistent with the block temperature.This shows that the exchange bias effect comes from the exchange coupling between the ferromagnetic phase and antiferromagnetic phase and disappears with the disappearance of ferromagnetic phase and antiferromagnetic phase at low temperature.?2?The effect of microstructure on exchange biasThe two two-layer perovskite manganese oxide Pr(Sr0.1Ca0.9)2Mn2O7 films of 720 nm thickness have been synthesized on Pt/Ti/SiO2/Si substrate by,and the surface morphology of the two films show uniform polygonal and triangular grains by SEM,respectively.The different microstructures cause the different pulsed laser deposition ferromagnetic and antiferromagnetic components in the two films,and have a certain effect on the exchange bias.However,the kind effect of microstructure is much smaller than the film thickness.?3?The effect of super-thick film on exchange biasPr(Sr0.1Ca0.9)2Mn2O7 film of 1.8?m thickness have been synthesized on Pt/Ti/SiO2/Si substrate by pulsed laser deposition,and the exchange bias has been researched.The vertical and horizontal exchange bias effect are 2.9×10-4emu/cm2 and-196 Oe at the temperature of 5K,cooling field of 7000 Oe and measuring field 7000 Oe in the film,and the exchange bias effect is stable.We speculate that structure anisotropy in the film has been strengthened with the increasing thickness,which is the main reason for the stronger exchange coupling between the ferromagnetic phase and antiferromagnetic phase and larger exchange bias effect. |
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