have gained a lot of interest. The iridates indeed display SOC which is on a similar energy scale than that of the electroncorrelation or the electronic bandwidth, [1] which favors new or exotic quantum electronic states. [2][3][4][5][6] However, in contrast to archetypical correlated 3d TMOs, the electron-electron correlation strength is often too small in the 5d TMOs to host ferromagnetism.For Sr 2 IrO 4 (n = 1), the SOC results in a spin-orbital mixed state of the Ir 4+ ion with a filled quadruplet pseudospin state J eff = 3/2 and a half-filled doublet J eff = 1/2. [7] Magnetic interaction of neighbored pseudospins leads to a basal (ab)-plane canted antiferromagnetic (AFM) Mottinsulator ground state with pseudospins locked to the oxygen octahedral rotation. [8][9][10] For n = 2, interlayer coupling weakens which leads to a spin-flop transition of the pseudospins with out-of-plane spin alignment along the c-axis and T N = 280 K. [11] In contrast, the perovskite phase SrIrO 3 (SIO) (n = ∞) displays paramagnetic semimetallic behavior due to an increased hybridization of Ir5d and O2p orbitals. [3,[12][13][14][15] Nevertheless, SIO is on the verge of a magnetic ground state and may display AFM or ferromagnetic (FM) properties as well, depending on the details of the Hubbard interaction U and the SOC. [12] Owing to a strong pseudospin-lattice coupling, [16] these can be finely tuned by structural modifications, especially with respect to the network of the corner-sharing IrO 6 octahedra which in turn enables a manipulation of the magnetism in SIO.The bulk structure of SIO consists in a distorted orthorhombic perovskite structure with in-phase and antiphase rotations of the IrO 6 octahedra (a − a − c + in Glazer notation). [17,18] However, a suppression of octahedral out-of-plane tilts, akin to the rotation pattern of Sr 2 IrO 4 can be achieved when ultrathin SIO films are epitaxially grown on cubic SrTiO 3 (STO) which concomitantly yields a metal-to-insulator transition (MIT). [19] Other type of structural distortions are likewise discussed as a possible source for magnetic properties of SIO. [20] For example, in SIO/STO superlattices the IrO 6 rotation pattern supports an AFM ground state, [21,22] where the ordering temperature T N can be controlled by the interlayer coupling, i.e., by the STO thickness [23] or epitaxial strain. [24] Meanwhile a lot of activities have been focused on SIO-based heterostructures including magnetic active layers, which seems The 5d iridium-based transition metal oxides have gained broad interest because of their strong spin-orbit coupling, which favors new or exotic quantum electronic states. On the other hand, they rarely exhibit more mainstream orders like ferromagnetism due to generally weak electron-electron correlation strength. Here, a proximity-induced ferromagnetic (FM) state with T C ≈ 100 K and strong magnetocrystalline anisotropy is shown in a SrIrO 3 (SIO) heterostructure via interfacial charge transfer by using a ferromagnetic insulator in contact with SIO. Electrical tra...
High entropy oxides (HEOs), based on the incorporation of multiple‐principal cations into the crystal lattice, offer the possibility to explore previously inaccessible oxide compositions and unconventional properties. Here it is demonstrated that despite the chemical complexity of HEOs external stimuli, such as epitaxial strain, can selectively stabilize certain magneto‐electronic states. Epitaxial (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4‐HEO thin films are grown in three different strain states: tensile, compressive, and relaxed. A unique coexistence of rocksalt and spinel‐HEO phases, which are fully coherent with no detectable chemical segregation, is revealed by transmission electron microscopy. This dual‐phase coexistence appears as a universal phenomenon in (Co0.2Cr0.2Fe0.2Mn0.2Ni0.2)3O4 epitaxial films. Prominent changes in the magnetic anisotropy and domain structure highlight the strain‐induced bidirectional control of magnetic properties in HEOs. When the films are relaxed, their magnetization behavior is isotropic, similar to that of bulk materials. However, under tensile strain, the hardness of the out‐of‐plane (OOP) axis increases significantly. On the other hand, compressive straining results in an easy OOP magnetization and a maze‐like magnetic domain structure, indicating the perpendicular magnetic anisotropy. Generally, this study emphasizes the adaptability of the high entropy design strategy, which, when combined with coherent strain engineering, opens additional prospects for fine‐tuning properties in oxides.
Laterally aligned SnO2 nanowires, which exhibit planar growth along crystallographically defined directions of a sapphire substrate surface, are superior for bio- and gas-sensing applications. Little is known about their cross-sectional geometry and the defect distribution within the nanowire cross section, although this substantially determines the electronic properties of the nanowires. In this study, SnO2 nanowires were grown on r-plane sapphire substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal the highly oriented growth of the SnO2 nanowires toward the substrate edges. High-resolution transmission electron microscopy (HRTEM) of the NW cross section and strain mapping allowed for analyzing the crystallographic alignment of the SnO2 NW to the sapphire substrate and the defect distribution within the SnO2 nanowire cross section. These techniques revealed a defect-free SnO2–Al2O3 interface and a high alignment of the SnO2 NW lattice toward the sapphire substrate along the NW width. The determined high defect density close to the nanowire surface will be discussed in comparison to freestanding SnO2 nanowires and SnO2 thin films on sapphire substrates considering the differences in the growth direction and the interface dimensionality.
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