Relaxor characteristics at the interfaces ofNdMnO3/SrMnO3/LaMnO3superlattices

Abstract

We have investigated the magnetic properties of transition-metal oxide superlattices with broken inversion symmetry composed of three different antiferromagnetic insulators, ͓NdMnO 3 / SrMnO 3 / LaMnO 3 ͔. In the superlattices studied here, we identify the emergence of a relaxor, glassylike behavior below T SG = 36 K. Our results offer the possibility to study and utilize magnetically metastable devices confined at nanoscale interfaces.Heterostructures of materials with strong electronelectron and electron-lattice interactions, the so-called correlated electron systems, are potential candidates for emergent interfacial properties including various forms of spin, charge, and orbital ordering absent in bulk materials. Promising examples include multilayers composed of insulators of LaAlO 3 and SrTiO 3 with interfaces displaying properties of quasi-two-dimensional electron gases, 1 superconductivity, 2 metallic conductivity, 3-5 and ferromagnetism ͑FM͒. 6 The multilayers composed of antiferromagnetic ͑AF͒ insulators in bulk forms, LaMnO 3 and SrMnO 3 are also examples of emergent electromagnetic properties at the interfaces between dissimilar manganites. 7-12 It has been demonstrated that these superlattices could posses FM order at the interfaces due to a charge reconstruction, although each parent material is an AF. 11 The competitive interaction between the reconstructed FM at interfaces and the AF states present far from the interface regions has been suggested to lead to a frustrated/glasslike behavior. 12,13 Small external perturbation in glasslike correlated electron thin-film devices, at a "caged" nanostructured interface, in particular, is expected to lead to high degree of tunability. These include, magnetoelectronics such as spin and charge memory devices at the atomic scale.Here we report on the relaxor and spin-glass ͑SG͒-like properties arising at the interface of superlattices, composed of insulating manganites: LaMnO 3 , SrMnO 3 , and NdMnO 3 , which are A-, G-, and A-type AF, respectively. Superlattices of ͓͑NdMnO 3 ͒ n / ͑SrMnO 3 ͒ n / ͑LaMnO 3 ͒ n ͔ m were grown epitaxially on single-crystalline SrTiO 3 substrates at an ambient oxygen/ozone mixture of 10 −4 Torr by layer-by-layer growth technology using the laser molecular-beam epitaxy technique. The details were reported in an earlier work. 14 Figure 1͑a͒ depicts a schematic drawing of a superlattice with n = 5 studied here with alternate A sites around the octahedra representing MnO 6 in the ABO 3 perovskite. The total thickness of the superlattices was kept approximately 500 Å varying ͑n , m͒ = ͑1 unit cell, 42͒, ͑2, 21͒, ͑5, 8͒, and ͑12, 4͒ in order to investigate the effect of the period. Structural characterization using synchrotron x-ray diffraction ͓Fig. 1͑b͔͒ along with the in situ reflection high-energy electron diffraction ͓Fig. 1͑c͔͒ indicate the presence of sharp interfaces with roughness less than 1 unit cell. The topography image performed using atomic force microscopy ͓Fig. 1͑d͔͒ confirms the surface roughness to be less than 1 un...

Tunable ferroelectricity in artificial tri-layer superlattices comprised of non-ferroic components

“…21. On the other hand, the relaxor behavior 21 could not be seen from the theoretical results, which describe a static and zero-temperature behavior revealing thus only the ground state of the system. Nevertheless, our DFT results indicate that the magnetic order and the origin of ferroelectricity are coupled (through the "trapping" and "hopping" of "down"-spin charge), therefore, ferroelectricity should have relaxor character too (as depicted in Fig.…”

“…This discovery allows for a wide range of new FE and ME materials and paves a long sought new path in the engineering 19 confirmed the presence of sharp interfaces with roughness less than one unit cell and a surface roughness of ~ 2 Å (ref. 21). The high quality of the samples was clarified further using detailed bulk magnetization and neutron reflectometry studies 21 .…”

“…The high quality of the samples was clarified further using detailed bulk magnetization and neutron reflectometry studies 21 . SL capacitors were prepared with fixed total thickness of 50 nm and varying (n, m) = (22, 2), (5,8) and (2,21); this was done in order to investigate the effect of periodicity on the polarization and the ME coupling. A schematic view of a typical capacitor fabricated for our study is shown in Fig.…”

“…(a) Capacitance-voltage (C-V) characteristics of various superlattices (SLs) measured at temperatures above their corresponding ferroelectric transition temperature (T c ). Data for(5,8),(2,21) and(22,2) SLs have been measured at 20 K, 25 K, and 50 K, respectively. No hysteresis between different voltage scanning directions is observed.…”

Magnetic Oxide Heterostructures

“…An example is so-called tricolor superlattices, with three constituent materials forming an ABC periodicity, in which inversion symmetry is broken, enabling interesting magnetoelectric phenomena (146)(147)(148). The addition of a third component can also induce magnetic frustration through the creation of two interfaces (A/B and B/C) with distinct and possibly competing interactions (149). The use of external electric or magnetic fields to alter interfacial charge transfer and/or orbital reconstructions may also prove to be a fruitful area of research, in particular in moving the study of interfacial magnetism along a more applied path.…”