Electromechanical Response from LaAlO₃/SrTiO₃ Heterostructures

LaAlO₃ ultrathin films, 10 unit cells in thickness, have been deposited epitaxially on TiO₂-terminated (001) SrTiO₃ substrates with various O₂ pressures. Electromechanical response from the LaAlO₃/SrTiO₃ heterostructures is studied using combined piezoresponse force microscopy, electrostatic force microscopy, and scanning Kelvin probe microscopy. Oxygen vacancies are found to be responsible for the observed piezoelectric response but only for samples deposited with an oxygen pressure lower than 10^–5 mbar. However, ambient humidity is demonstrated to have a significant effect on the electromechanical response. The observations are discussed in terms of modulations on the intrinsic electrostriction in LAO/STO by an electric field induced by nonuniform distribution of either oxygen vacancies in the bulk or ionic adsorbates on the surface of LAO

Spin-Glass-Like Behavior and Topological Hall Effect in SrRuO₃/SrIrO₃ Superlattices for Oxide Spintronics Applications

The heterostructure interface provides a powerful platform for exploring rich emergent phenomena, such as interfacial superconductivity and nontrivial topological surface states. Here, SrRuO₃/SrIrO₃ superlattices were epitaxially synthesized. The magnetic and magneto-transport properties of these superlattices were characterized. A broad cusp-type splitting in the zero-field-cooling/field-cooling temperature-dependent magnetization and magnetization relaxation, which follows the modified stretched function model, accompanied by double hysteresis magnetization loops were demonstrated. These physical effects were modulated by the SrIrO₃ layer thickness, which confirms the coexistence of interfacial spin glass and ferromagnetic ordering in the superlattices. In addition, the topological Hall effect was observed at low temperatures, and it is weakened with the increase of the SrIrO₃ layer thickness. These results suggest that a noncoplanar spin texture is generated at the SrRuO₃/SrIrO₃ interfaces because of the interfacial Dzyaloshinskii–Moriya interaction. This work demonstrates that SrIrO₃ can effectively induce interfacial Dzyaloshinskii–Moriya interactions in superlattices, which would serve as a mechanism to develop spintronic devices with perovskite oxides

Structure, Magnetism, and Tunable Negative Thermal Expansion in (Hf,Nb)Fe₂ Alloys

Structure, Magnetism, and Tunable Negative Thermal Expansion in (Hf,Nb)Fe₂ Alloy

Exceptionally High Piezoelectric Coefficient and Low Strain Hysteresis in Grain-Oriented (Ba, Ca)(Ti, Zr)O₃ through Integrating Crystallographic Texture and Domain Engineering

Both low strain hysteresis and high piezoelectric performance are required for practical applications in precisely controlled piezoelectric devices and systems. Unfortunately, enhanced piezoelectric properties were usually obtained with the presence of a large strain hysteresis in BaTiO₃ (BT)-based piezoceramics. In this work, we propose to integrate crystallographic texturing and domain engineering strategies into BT-based ceramics to resolve this challenge. [001]_c grain-oriented (Ba_0.94Ca_0.06)­(Ti_0.95Zr_0.05)­O₃ (BCTZ) ceramics with a texture degree as high as 98.6% were synthesized by templated grain growth. A very high piezoelectric coefficient (<i>d</i>₃₃) of 755 pC/N, and an extremely large piezoelectric strain coefficient (<i>d</i>₃₃* = 2027 pm/V) along with an ultralow strain hysteresis (<i>H</i>_s) of 4.1% were simultaneously achieved in BT-based systems for the first time, which are among the best values ever reported on both lead-free and lead-based piezoceramics. The exceptionally high piezoelectric response is mainly from the reversible contribution, and can be ascribed to the piezoelectric anisotropy, the favorable domain configuration, and the formation of smaller sized domains in the BCTZ textured ceramics. This study paves a new pathway to develop lead-free piezoelectrics with both low strain hysteresis and high piezoelectric coefficient. More importantly, it represents a very exciting discovery with potential application of BT-based ceramics in high-precision piezoelectric actuators

Zero Thermal Expansion in Magnetic and Metallic Tb(Co,Fe)₂ Intermetallic Compounds

Due to the advantage of invariable length with temperatures, zero thermal expansion (ZTE) materials are intriguing but very rare especially for the metals based compounds. Here, we report a ZTE in the magnetic intermetallic compounds of Tb­(Co,Fe)₂ over a wide temperature range (123–307 K). A negligible coefficient of thermal expansion (α_l = 0.48 × 10^–6 K^–1) has been found in Tb­(Co_1.9Fe_0.1). Tb­(Co,Fe)₂ exhibits ferrimagnetic structure, in which the moments of Tb and Co/Fe are antiparallel alignment along the <i>c</i> axis. The intriguing ZTE property of Tb­(Co,Fe)₂ is formed due to the balance between the negative contribution from the Tb magnetic moment induced spontaneous magnetostriction and the positive role from the normal lattice expansion. The present ZTE intermetallic compounds are also featured by the advantages of wide temperature range, high electrical conductivity, and relatively high thermal conductivity

Zero Thermal Expansion in Magnetic and Metallic Tb(Co,Fe)₂ Intermetallic Compounds

Due to the advantage of invariable length with temperatures, zero thermal expansion (ZTE) materials are intriguing but very rare especially for the metals based compounds. Here, we report a ZTE in the magnetic intermetallic compounds of Tb­(Co,Fe)₂ over a wide temperature range (123–307 K). A negligible coefficient of thermal expansion (α_l = 0.48 × 10^–6 K^–1) has been found in Tb­(Co_1.9Fe_0.1). Tb­(Co,Fe)₂ exhibits ferrimagnetic structure, in which the moments of Tb and Co/Fe are antiparallel alignment along the <i>c</i> axis. The intriguing ZTE property of Tb­(Co,Fe)₂ is formed due to the balance between the negative contribution from the Tb magnetic moment induced spontaneous magnetostriction and the positive role from the normal lattice expansion. The present ZTE intermetallic compounds are also featured by the advantages of wide temperature range, high electrical conductivity, and relatively high thermal conductivity