S H Roshna, Prellier W, Padhan P
Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India.
Laboratoire CRISMAT, CNRS UMR 6508, ENSICAEN, 6 Bd du Marechal Juin, F-14050 Caen Cedex, France.
Nanoscale. 2020 Feb 27;12(8):5151-5158. doi: 10.1039/d0nr00620c.
Magnetocaloric effect in (111)-oriented La0.7Sr0.3MnO3-SrRuO3 (LSMO-SRO) superlattices grown with both the stacking orders by reversing the individual layer thickness on (111)-oriented SrTiO3(STO) substrates using the pulsed laser deposition technique has been studied. Pseudomorphic growth with 0.64% in-plane tensile strain in [11 unit cell (u.c.)SRO/3u.c.LSMO]×15 superlattice is favourable for a larger change in entropy (ΔSM) as compared to relaxed growth with in-plane compressive strain in [11u.c.LSMO/3u.c.SRO]×15 superlattice. The reduction of ΔSM in [11u.c.LSMO/3u.c.SRO]×15 could be due to the orientation-dependent in-phase and out-of-phase tilt of the unit cell between ±1° along the 103pc of the {103}pc, which softens the exchange coupling and leads to the faster alignment of the magnetization near the Curie temperature (TC). Stabilization of the orthorhombic phase of LSMO in the superlattices with both stacking orders is evidenced from the existence of anomaly around the TC of LSMO and SRO in the temperature-dependent phonon frequency shifts. Reduction in symmetry of LSMO from the rhombohedral to orthorhombic structure modulates the Mn-O-Mn bond length and angles, which induces the spin reorientations and hence, modifies the electronic and magnetic properties in these LSMO-SRO superlattices. The ΔSM of these superlattices suggest that the strain, magnitude of the magnetic field, volume and magnetization of the ferromagnet can control the magnetocaloric effect. These results will be useful for designing the magnetic entropy based devices to improve renewable energy systems.
利用脉冲激光沉积技术，在（111）取向的SrTiO3（STO）衬底上通过反转各层厚度来生长具有两种堆叠顺序的（111）取向的La0.7Sr0.3MnO3-SrRuO3（LSMO-SRO）超晶格，并对其磁热效应进行了研究。与在[11个晶胞（u.c.）SRO/3u.c.LSMO]×15超晶格中具有面内压缩应变的弛豫生长相比，在[11u.c.SRO/3u.c.LSMO]×15超晶格中具有0.64%面内拉伸应变的赝晶生长有利于更大的熵变（ΔSM）。[11u.c.LSMO/3u.c.SRO]×15中ΔSM的降低可能是由于沿着{103}pc的103pc在±1°之间晶胞的取向相关的同相和异相倾斜，这软化了交换耦合并导致在居里温度（TC）附近磁化更快地取向。在具有两种堆叠顺序的超晶格中，LSMO正交相的稳定从与温度相关的声子频率偏移中LSMO和SRO的TC附近异常的存在得到证明。LSMO从菱面体结构到正交结构的对称性降低调节了Mn-O-Mn键长和键角，这诱导了自旋重新取向，从而改变了这些LSMO-SRO超晶格中的电子和磁性。这些超晶格的ΔSM表明，铁磁体的应变、磁场大小、体积和磁化强度可以控制磁热效应。这些结果将有助于设计基于磁熵的器件以改善可再生能源系统。
