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

我们研究了在场致铁磁金属- fmm_转变发生的温度区域内，a (La,Pr)_<1.2>Sr_<1.8>Mn_2O_7双层锰矿单晶ab面和c轴上的压力对磁致伸缩的影响。为了比较，我们还研究了相应温度下磁化曲线的压力依赖性。施加的压力减小了FMM过渡的临界场，增强了剩余磁致伸缩。观察到残余晶格弛豫的异常压力效应，这与沿c轴的残余磁化的压力效应相似。这些发现可以从双重交换相互作用驱动的FMM状态通过施加压力得到加强的观点来理解。接下来，我们报道了单晶（La_<0.4>Pr_<0.6>）_<1.2>Sr_<1.8>Mn_2O_7双层锰矿的阶梯晶格转变，同时伴有磁化和磁阻跳变，并研究了场诱导的顺磁绝缘体到铁磁金属相的一阶转变的超清晰性，同时伴随着电阻的大幅下降。我们的研究结果支持了突变磁致伸缩与存在于非均匀顺磁绝缘相中的轨道挫折密切相关，而不是与竞争两相之间的马氏体情况密切相关。

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.