强磁场退火处理对La_(0.5)Ca_(0.5)MnO_(3)薄膜晶粒尺寸演化和磁性能的影响

Evolution of Grain Size and Magnetic Properties in La_(0.5)Ca_(0.5)MnO_(3) Thin Films by High Magnetic Field Annealing

采用脉冲激光沉积法制备了La_(0.5)Ca_(0.5)MnO_(3)(LCMO)薄膜,然后在不同强磁场作用下进行原位后退火处理。利用XRD、FESEM和SQUID对薄膜进行微结构表征和磁特性测量。结果显示,强磁场退火使得薄膜的面外晶格参数拉长,晶粒尺寸明显增大,同时使低温磁化强度降低。通过建立强磁场下的晶粒生长速率方程对晶粒尺寸演化机理做了分析。分析认为,强磁场引入的额外驱动力降低了LCMO薄膜的临界晶粒尺寸,有利于晶粒生长。此外,本文通过建立一个基于相分离的反铁磁-铁磁核壳模型对薄膜的磁结构演化进行了探讨。认为晶粒尺寸增大导致铁磁相体积分数下降,从而导致低温磁化强度下降。

La_(0.5)Ca_(0.5)MnO_(3)(LCMO)thin films were prepared by the pulsed laser deposition method and then annealed in situ under different high magnetic fields.The microstructures and magnetic properties of the films were characterized and measured by XRD,FESEM and SQUID.The results show that an elongation in out-of-plane lattice parameter,a dramatic increase in grain size,and a decrease in low-temperature magnetization can be observed in the LCMO films annealed in high magnetic fields.The evolution mechanism on grain size is investigated by establishing a rate equation of grain growth,including the effect of a high magnetic field.It is argued that as an extra driving force of grain growth,the introduction of a high magnetic field leads to a lowering in critical grain size in LCMO films,favoring the grain growth.In addition,an antiferromagnetic-ferromagnetic core-shell model based on phase separation is proposed to understand the evolution of magnetic configuration.It is proposed that the increase in grain size results in a decrease in volume fraction of ferromagnetic phase,and thus a decrease in low-temperature magnetization.