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

我们研究了(La，Pr)_t；1.2&gt；Sr_&lt；1.8&gt；Mn_2O_7双层结构锰氧化物单晶在发生场感生铁磁金属_FMM_1相变的温度范围内，在ab面上和c轴方向的磁致伸缩压力效应。为了比较，我们还考察了相应温度下磁化曲线的压力依赖关系。外加压力降低了FMM转变的临界场，增强了剩余磁致伸缩。观察到剩余晶格弛豫的反常压力效应，与沿c轴的剩余磁化强度的压力效应相似。接下来，我们报道了单晶(La_&lt；0.4&gt；Pr_&lt；0.6&gt；)_&lt；1.2&gt；Sr_&lt；1.8&gt；Mn_2O_7双层锰氧化物的阶梯状晶格相变，并研究了伴随磁化和磁阻跳跃的场诱导从顺磁绝缘体到铁磁金属相的一阶相变的超尖锐性质，并伴随着电阻的大幅下降。我们的发现支持这种突然的磁致伸缩与非均匀顺磁绝缘相中存在的轨道受挫密切相关，而不是与竞争两相之间的马氏体情形密切相关。

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.