Modulating Magnetism in Ferroelectric Polymer-Gated Perovskite Manganite Films with Moderate Gate Pulse Chains.

Most previous attempts on achieving electric-field manipulation of ferromagnetism in complex oxides, such as La0.66Sr0.33MnO3 (LSMO), are based on electrostatically induced charge carrier changes through high-k dielectrics or ferroelectrics. Here, the use of a ferroelectric copolymer, polyvinylidene fluoride with trifluoroethylene [P(VDF-TrFE)], as a gate dielectric to successfully modulate the ferromagnetism of the LSMO thin film in a field-effect device geometry is demonstrated. Specifically, through the application of low-voltage pulse chains inadequate to switch the electric dipoles of the copolymer, enhanced tunability of the oxide magnetic response is obtained, compared to that induced by ferroelectric polarization. Such observations have been attributed to electric field-induced oxygen vacancy accumulation/depletion in the LSMO layer upon the application of pulse chains, which is supported by surface-sensitive-characterization techniques, including X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism. These techniques not only unveil the electrochemical nature of the mechanism but also establish a direct correlation between the oxygen vacancies created and subsequent changes to the valence states of Mn ions in LSMO. These demonstrations based on the pulsing strategy can be a viable route equally applicable to other functional oxides for the construction of electric field-controlled magnetic devices.

High-Temperature Anomalous Hall Effect in a Transition Metal Dichalcogenide Ferromagnetic Insulator Heterostructure.

Integration of transition metal dichalcogenides (TMDs) on ferromagnetic materials (FM) may yield fascinating physics and promise for electronics and spintronic applications. In this work, high-temperature anomalous Hall effect (AHE) in the TMD ZrTe2 thin film using a heterostructure approach by depositing it on a ferrimagnetic insulator YIG (Y3Fe5O12, yttrium iron garnet) is demonstrated. In this heterostructure, significant anomalous Hall effect can be observed at temperatures up to at least 400 K, which is a record high temperature for the observation of AHE in TMDs, and the large RAHE is more than 1 order of magnitude larger than those previously reported values in topological insulators or TMD-based heterostructures. A complicated interface with additional ZrO2 and amorphous YIG layers is actually observed between ZrTe2 and YIG. The magnetization of interfacial reaction-induced ZrO2 and YIG is believed to play a crucial role in the induced high-temperature AHE in the ZrTe2. These results present a promising system for the spintronic device applications, and it may shed light on the designing approach to introduce magnetism to TMDs at room temperature.

Effect of Thickness on the Optical and Electrical Properties of ITO/Au/ITO Sandwich Structures.

Tin-doped indium oxide (ITO)/Au/ITO sandwich structures with varying top and bottom ITO film thicknesses were deposited by magnetron sputtering. The effects of varying thickness of the two ITO films on the structural, electrical, and optical properties of the sandwich structures were investigated. X-ray diffraction spectra showed that by inserting an ultrathin Au film, the average grain size of the top ITO layer was significantly increased, but not for the bottom one. The optical properties of the sandwich structures were measured by transmittance measurement and spectroscopic ellipsometry. In the symmetric structure, where the top and the bottom ITO layers had the same thickness, we demonstrated that the crossover wavelength can be changed from the visible range (830 nm) to the near-infrared range (1490 nm) by increasing the top as well as bottom ITO thickness, corresponding to a plasmonic tuning ability of over 600 nm. The evaluation of this trilayer structure as a plasmonic device was asserted based on three quality factors. A comparison of the performance of this trilayer structure with conventional materials was also discussed.

A ferroelectric relaxor polymer-enhanced p-type WSe2 transistor.

WSe2 has attracted extensive attention for p-FETs due to its air stability and high mobility. However, the Fermi level of WSe2 is close to the middle of the band gap, which will induce a high contact resistance with metals and thus limit the field effect mobility. In this case, a high work voltage is always required to achieve a large ON/OFF ratio. Herein, a stable WSe2 p-doping technique of coating using a ferroelectric relaxor polymer P(VDF-TrFE-CFE) is proposed. Unlike other doping methods, P(VDF-TrFE-CFE) not only can modify the Fermi level of WSe2 but can also act as a high-k gate dielectric in an FET. Dramatic enhancement of the field effect hole mobility from 27 to 170 cm2 V-1 s-1 on a six-layer WSe2 FET has been achieved. Moreover, an FET device based on bilayer WSe2 with P(VDF-TrFE-CFE) as the top gate dielectric is fabricated, which exhibits high p-type performance over a low top gate voltage range. Furthermore, low-temperature experiments reveal the influence of the phase transition of P(VDF-TrFE-CFE) on the channel carrier density and mobility. With a decrease in temperature, field effect hole mobility increases and approaches up to 900 cm2 V-1 s-1 at 200 K. The combination of the p-doping and gating with P(VDF-TrFE-CFE) provides a promising solution for obtaining high-performance p-FET with 2D semiconductors.

Patterning of L10 FePt nanoparticles with ultra-high coercivity for bit-patterned media.

L10-ordered FePt nanoparticles (NPs) with ultra-high coercivity were directly prepared from a new metallopolyyne using a one-step pyrolysis method. The chemical ordering, morphology and magnetic properties of the as-synthesized FePt NPs have been studied. Magnetic measurements show the coercivity of these FePt NPs is as high as 3.6 T. Comparison of NPs synthesized under the Ar and Ar/H2 atmospheres shows that the presence of H2 in the annealing environment influences the nucleation and promotes the growth of L10-FePt NPs. Application of this metallopolymer for bit-patterned media was also demonstrated using nanoimprint lithography.