A new approach to prepare surface-functionalized magnetic nanoparticles by synthesis of poly(methacrylic acid) (PMAA) coated maghemite nanoparticles in aqueous solution is reported. Maghemite (c-Fe 2 O 3 ) nanoparticles with an average diameter of 8 ¡ 2 nm were fabricated and subsequently coated with PMAA by emulsion polymerization. The FTIR study and thermal analysis confirmed the chemical adsorption of methacrylic acid on the maghemite nanoparticle surface, and suggested a symmetrical carboxylate bonding. The free carboxyl group of PMAA, which was verified by FTIR spectroscopy and zeta potential measurement, provided the site for immobilization of foreign molecules. The PMAA coated maghemite nanoparticles were demonstrated as potential magnetically targeted drug carriers by adsorbing an anti-cancer drug (carboplatin) via the ion-dipole interaction between CO 2 2 of PMAA and carboplatin.

Topological Hall effect (THE), appearing as bumps and/or dips in the Hall resistance curves, is considered as a hallmark of the skyrmion spin texture originated from the inversion symmetry breaking and spin–orbit interaction. Recently, Néel‐type skyrmion is proposed based on the observed THE in 5d transition metal oxides heterostructures such as SrRuO3/SrIrO3 bilayers, where the interfacial Dzyaloshinskii–Moriya interaction (DMI), due to the strong spin–orbit coupling (SOC) in SrIrO3 and the broken inversion symmetry at the interface, is believed to play a significant role. Here the emergence of THE in SrRuO3 single layers with thickness ranging from 3 to 6 nm is experimentally demonstrated. It is found that the oxygen octahedron rotation in SrRuO3 also has a significant effect on the observed THE. Furthermore, the THE may be continuously tuned by an applied electrical field. It is proposed that the large SOC of Ru ions together with the broken inversion symmetry, mainly from the interface, produce the DMI that is responsible for the observed THE. The emergence of the gate‐tunable DMI in SrRuO3 single layer may stimulate further investigations of new spin–orbit physics in strong SOC oxides.

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Monodisperse β-NaYF4:Yb,Er nanocrystals with mean sizes of 11, 40, and 110 nm were synthesized by a thermal decomposition solvothermal process to better understand the relationship between particle size and optical properties. A systematic study of luminescence intensity versus size revealed that both visible upconversion and infrared downconversion emission intensities decrease with decreasing nanocrystal size. The intrinsic quantum efficiency of the infrared 4 I 13/2 → 4 I 15/2 downconversion transition was studied in great detail since this specific transition allows us to quantify the contribution of nonradiative losses more easily than the observed upconversion transitions. The intrinsic quantum efficiency of the 4 I 13/2→4 I 15/2 transition decreased from 50% (110 nm) to 15% (11 nm). Multiphonon relaxation and −OH quenching was studied in these materials by measuring the vibrational characteristics of β-NaYF4:Yb,Er nanospheres. While multiphonon relaxation exhibited increased contribution to nonradiative decay, −OH quenching rates were calculated to be ∼4 orders of magnitude higher than that of the multiphonon relaxation. Therefore, surface −OH quenching effects were concluded to be primarily responsible for the observed dependence of emission intensity versus particle size.

Brain-inspired computing is an emerging field, which intends to extend the capabilities of information technology beyond digital logic. The progress of the field relies on artificial synaptic devices as the building block for brainlike computing systems. Here, we report an electronic synapse based on a ferroelectric tunnel memristor, where its synaptic plasticity learning property can be controlled by nanoscale interface engineering. The effect of the interface engineering on the device performance was studied. Different memristor interfaces lead to an opposite virgin resistance state of the devices. More importantly, nanoscale interface engineering could tune the intrinsic band alignment of the ferroelectric/metal-semiconductor heterostructure over a large range of 1.28 eV, which eventually results in different memristive and spike-timing-dependent plasticity (STDP) properties of the devices. Bidirectional and unidirectional gradual resistance modulation of the devices could therefore be controlled by tuning the band alignment. This study gives useful insights on tuning device functionalities through nanoscale interface engineering. The diverse STDP forms of the memristors with different interfaces may play different specific roles in various spike neural networks.

A combined experimental and computational study was carried out to investigate magnetic properties of NiO nanostructures. Remarkable size-dependent magnetism was discovered. Uniform amorphous NiO showed a dominated antiferromagnetic interaction and an ordering temperature of 3.5 K. NiO clusters ͑up to 1 nm͒ tend to be ferromagnetic interaction with an ordering temperature of 35 K, accompanied by high magnetization ͑105 emu/ g͒ and a spin-glass behavior. NiO nanocrystals ͑Ͼ2 nm͒ were found to be antiferromagnetic with uncompensated surface magnetization and shifted hysteresis due to the core-shell interactions.

We report on the efficient spin-orbit torque (SOT) switching in a single ferromagnetic layer induced by a new type of inversion asymmetry, the composition gradient. The SOT of 6-to 60-nm epitaxial FePt thin films with a L1 0 phase is investigated. The magnetization of the FePt single layer can be reversibly switched by applying electrical current with a moderate current density. Different from previously reported SOTs which either decreases with or does not change with the film thickness, the SOT in FePt increases with the film thickness. We found the SOT in FePt can be attributed to the composition gradient along the film normal direction. A linear correlation between the SOT and the composition gradient is observed. This Rapid Communication introduces a platform to engineer large SOTs for lower-power spintronics.

Strain engineering is an effective way to modify functional properties of thin films. Recently, the importance of octahedral rotations in pervoskite films has been recognized in discovering and designing new functional phases. Octahedral behavior of SrRuO3 film as a popular electrode in heterostructured devices is of particular interest for its probable interfacial coupling of octahedra with the functional overlayers. Here we report the strain engineering of octahedral rotations and physical properties that has been achieved in SrRuO3 films in response to the substrate-induced misfit strains of almost the same amplitude but of opposite signs. It shows that the compressively strained film on NdGaO3 substrate displays a rotation pattern of a tetragonal phase whilst the tensilely strained film on KTaO3 substrate has the rotation pattern of the bulk orthorhombic SrRuO3 phase. In addition, the compressively strained film displays a perpendicular magnetic anisotropy while the tensilely strained film has the magnetic easy axis lying in the film plane. The results show the prospect of strain engineered octahedral architecture in producing desired property and novel functionality in the class of perovskite material.