We investigated the structural, magnetic, and transport properties of polycrystalline doping systems La 0.5 Sr 0.5 Mn 1−x Ru x O 3 ͑0 ഛ x ഛ 0.15͒ with ferromagnetic matrix and La 0.45 Sr 0.55 Mn 1−y Ru y O 3 ͑0 ഛ y ഛ 0.5͒ with antiferromagnetic matrix. X-ray photoelectron spectroscopy shows that Ru ions exist mainly in the form of Ru 4+ while there also exist a small quantity of Ru 5+ . For the low doping samples ͓0.05ഛ x͑y͒ ഛ 0.15͑0.2͔͒, the ferromagnetism is enhanced and Curie temperature T C rises with increasing Ru doping level, but T C is much higher than the temperature T IM corresponding to insulating-metallic transition. For the high doping samples ͑0.3ഛ y ഛ 0.5͒, oppositely the ferromagnetism is suppressed and the insulating property is enhanced with further increasing Ru doping level. These results show that there is an exchange interaction between Mn 3+ and Ru 4+ ͑Ru 5+ ͒. The electron spin resonance spectra clearly and directly inspect that the interaction between Mn 3+ and Ru 4+ ͑Ru 5+ ͒ is ferromagnetic. Furthermore, the electron spin resonance spectra also show that a Ru-Ru antiferromagnetic interaction takes place in the high doping region ͑y = 0.4, 0.5͒. We explained the disagreement between T C and T IM .

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Phononic crystals (PnCs) have attracted much attention due to their great potential for dissipation engineering and propagation manipulation of phonons. Notably, the excellent electrical and mechanical properties of graphene make it a promising material for nanoelectromechanical resonators. Transferring a graphene flake to a prepatterned periodic mechanical structure enables the realization of a PnC with on-chip scale. Here, we demonstrate a nanoelectromechanical periodic array by anchoring a graphene membrane to a 9 × 9 array of standing nanopillars. The device exhibits a quasi-continuous frequency spectrum with resonance modes distributed from ∼120 MHz to ∼980 MHz. Moreover, the resonant frequencies of these modes can be electrically tuned by varying the voltage applied to the gate electrode sitting underneath. Simulations suggest that the observed band-like spectrum provides an experimental evidence for PnC formation. Our architecture has large fabrication flexibility, offering a promising platform for investigations on PnCs with electrical accessibility and tunability.

In this letter, Nd0.5Sr0.5Mn1- xGaxO3 (0.0⩽x⩽0.075) manganites have been investigated. Diffuse satellite spots and streaks can be seen in transmission electron microscopy and the antiferromagnetic signal in electron spin resonance also occur early at 235 K which is much higher than the usually defined TCO of the Nd0.5Sr0.5Mn1- xGaxO3 sample, indicating that the charge ordering phase already appears in the ferromagnetic regions (TC=250 K). This charge ordering phase is submerged by the ferromagnetic phase so that it is invisible in routine measurements. As the TC moves to lower temperature with Ga doping, the charge ordering phase exhibits itself gradually around 240 K.

In this paper, we report unusual thermal hysteresis behaviour in half-doped manganites Nd0.5Sr0.5−xCaxMnO3 (0.0 ⩽ x ⩽ 0.50). For 0.05 ⩽ x < 0.25 samples, the magnetization curves show a counterclockwise hysteresis loop. For 0.25 < x ⩽ 0.40 samples, however, they exhibit a clockwise loop. The inverse hysteretic behaviour stems from the competition between two kinds of strain, namely, the compressive strain and the tensile strain. The former produces a counterclockwise thermal hysteresis while the latter leads to a clockwise one. In the meantime, a magnetic instability is observed and the strain relaxation should be the main reason for it.

We investigated the magnetotransport properties of polycrystalline La0.45Sr0.55Mn1−xCoxO3 (0≤x≤0.15). Ferromagnetism is enhanced with the doping of Co ions in La0.45Sr0.55MnO3, but the antiferromagnetism is nearly destroyed in the low-temperature region. The Mn3+–Mn4+ double-exchange (DE) and Co2+–Mn4+ ferromagnetic (FM) superexchange interactions are mainly responsible for the magnetic properties of the doped system. With increased Co doping, the insulating properties and the magnetoresistance (MR) effect are simultaneously enhanced. This indicates that the Co doping strengthens both the Mn3+–Mn4+ DE and Co2+–Mn4+ FM superexchange interactions. The Co doping increases the disorder in the system, causing the MR effect to increase with decreasing temperature.

The electronic transport and magnetism in half-doped Nd0.50Ca0.25Sr0.25MnO3 manganites have been investigated. Contrary to general half-doped system, it only displays a paramagnetic-ferromagnetic phase transition associated with an insulator-metal transition instead of with any features of charge ordering. With the decrease of temperature, an electronic phase separation and spin glass state occur in low temperature. We suggest that the A-site cation disorder induced by the size mismatch between Sr2+ ion and Ca2+ ion is mainly responsible for this phenomenon.

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