Pressure effect on phonon physics and slow dynamics of Griffith phase in bilayered manganese oxides

本文研究了（La，Pr）<1.2>_Sr_Mn_2O_7<1.8>双层锰氧化物单晶在磁场诱导铁磁金属_FMM_转变温度范围内ab平面和沿着c轴的磁致伸缩的压力效应。为了比较，我们还研究了在相应温度下磁化曲线的压力依赖性。外加压力降低了FMM转变的临界场，增强了回复磁致伸缩。观察到一个异常的压力效应的rexton晶格弛豫和rexton磁化沿着c轴的压力效应相似。这些发现是从双交换作用驱动的FMM态被压力强化的观点来理解的。其次，我们报道了（La_<0.4>Pr_<0.6>）_<1.2>Sr_<1.8>Mn_2O_7双层锰氧化物单晶的阶梯状晶格转变，伴随着磁化和磁阻的跳跃，并检查场致第一波的超尖锐性质-从顺磁绝缘体到铁磁金属相的有序转变伴随着电阻的巨大降低。我们的研究结果支持，突然的磁致伸缩是密切相关的轨道挫折存在于不均匀的顺磁绝缘相，而不是竞争的两相之间的马氏体的情况。

We have studied the pressure effect on magnetostriction, both in the ab plane and along the c axis of a (La,Pr)_<1.2>Sr_<1.8>Mn_2O_7 bilayered manganite single crystal over the temperature region where the field-induced ferromagnetic metal_FMM_transition takes place. For comparison, we have also examined the pressure dependence of magnetization curves at the corresponding temperatures. The applied pressure reduces the critical field of the FMM transition and it enhances the remanent magnetostriction. An anomalous pressure effect on the remanent lattice relaxation is observed and is similar to the pressure effect on the remanent magnetization along the c axis. These findings are understood from the viewpoint that the double-exchange interaction-driven FMM state is strengthened by the application of pressure.Next, we have reported a steplike lattice transformation of single crystalline (La_<0.4>Pr_<0.6>)_<1.2>Sr_<1.8>Mn_2O_7 bilayered manganite accompanied by both magnetization and magnetoresistive jumps, and examine the ultrasharp nature of the field-induced first-order transition from a paramagnetic insulator to a ferromagnetic metal phase accompanied by a huge decrease in resistance. Our findings support that the abrupt magnetostriction is closely related to an orbital frustration existing in the inhomogeneous paramagnetic insulating phase rather than a martensitic scenario between competing two phases.