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SrIrO3 (SIO) thin films were epitaxially grown on (001)-oriented 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) single-crystal substrates. Upon applying electric fields to the piezoelectric PMN-PT along the thickness direction, the electronic transport properties of SIO films can be in situ tuned and modulated by non-180° ferroelectric domain rotation-induced strain, piezoelectric strain, and rhombohedral-to-tetragonal structural phase transition-induced strain in the PMN-PT layer, respectively. Moreover, the weak negative magnetoresistance (MR) of the 60-nm SIO films could be modified by applying an electric field to the PMN-PT layer. At T = 2 K, upon the application of E = 4 kV/cm to the PMN-PT, MR at H = 9 T is reduced by 14.2% as compared to that under zero electric field, indicating in-plane compressive strain-induced suppression of the influence of quantum corrections to the conductivity in the SIO film. These results demonstrate that the electric-field controllable lattice strain is a simple approach to get insight into the strain-property relationships of 5 d iridate thin films.

Temperature dependence of resistivity in quasi-two-dimensional purple bronzes AMo6O17 (A=Na, K, and Tl) has been comparatively studied between 2 and 300 K at different magnetic fields. Huge positive magnetoresistance (MR) behavior below the Peierls transition temperature TP∼110 K was found in both K/Tl purple bronzes for H∥c, but only a weak one in the Na purple bronze. At lower temperature TM∼16 K, a second anomaly of the resistivity, which moved to higher temperatures under a magnetic field, was also observed in both K/Tl compounds, with no corresponding anomaly in the Na purple bronze. For H⊥c, the MR effect becomes much weaker in all three compounds. These results suggest that the second anomaly is possibly related to the second Peierls instability, and the huge MR effect results from the large modification of the third FS along the [100] direction induced by the magnetic field, in which the third FS is imperfectly nested in K/Tl purple bronzes and absent in the Na purple bronze.

Various giant magnetoresistance material structures were patterned and studied for their potential as memory elements. The preferred memory element, based on pseudo-spin valve structures, was designed with two magnetic stacks (NiFeCo/CoFe) of different thickness with Cu as an interlayer. The difference in thickness results in dissimilar switching fields due to the shape anisotropy at deep submicron dimensions. It was found that a lower switching current can be achieved when the bits have a word line that wraps around the bit 1.5 times. Submicron memory elements integrated with complementary metal–oxide–semiconductor (CMOS) transistors maintained their characteristics and no degradation to the CMOS devices was observed. Selectivity between memory elements in high-density arrays was demonstrated.

Submicron room-temperature ferromagnets are formed in GaAs semiconductors through a simple process of ion implantation and subsequent heat treatment. The ferromagnetic structures are studied using magnetic force microscopy. Magnetization switching of single-domain particles has been directly imaged in applied magnetic fields. In order to understand the images of magnetic structures taken under external fields, we have characterized the magnetic force microscopy (MFM) probes by imaging microfabricated current-carrying strips in applied magnetic fields. Patterned micrometer scale lines containing submicron magnetic structures on GaAs are fabricated using lithography in conjunction with broad beam ion implantation.

Magnetic properties of (Ga,Mn)As digital ferromagnetic heterostructures have been investigated by polarized neutron reflectometry and magnetometry. Tc of three samples with 20, 50, and 100 ML GaAs spacers ranges from 30 to 40 K. The saturation magnetization of three samples exhibits a pronounced tail extending over 50 K above Tc in addition to a temperature-independent background. For the 50 ML sample, PNR measurements show a similar tail but no background. These behaviors can be explained by a two-step ordering process. In the tail region, two-dimensional islands first individually become ferromagnetic. Long-range order develops as the temperature is decreased below Tc.

We found that the coercivity of electron-beam patterned nanoscale NiFe and Co lines (width ranging from 55 nm to 1 μm) has a distinct inverse-width dependence when the film thickness is greater than 3.5 nm. This inverse-width dependence is consistent with a nucleation picture in which the magnetization reversal is controlled by a small nucleus, which spreads across the width of the nanoline but is independent of the length. However, the inverse-width dependence breaks down for the narrowest NiFe lines at room temperature in films below 3.5 nm in thickness. In this thickness regime the coercivity drops rapidly as a function of decreasing width as the controlling nucleus size approaches the superparamagnetic limit. The Arrhenius–Neel equation for this equivalent volume very effectively models the data. As the temperature is decreased, the coercivity of the narrowest lines rapidly increases and the inverse-width trend is recovered.

The dynamics of two domain walls (DWs) in a system of two nanowires with perpendicular magnetocrystalline anisotropy (PMA) was investigated by micromagnetic simulation. It was found that without applied current, the motion mode of DWs is translational motion plus oscillation. Different from its in-plane counterpart, in a two-PMA-nanowire system, the oscillation of DWs before encountering is quite intrinsic—the frequency and the amplitude only depend on the separation between nanowires and the material of the nanowires, and have no relationship with applied current and the distance between two DWs. When applying proper currents, the coupled DWs will only oscillate without performing translational motion. The oscillation frequency can reach several GHz. Besides being tuned in a large range by varying the nanowire separation, the oscillation frequency can also be slightly modified by adjusting the magnetic anisotropy (K) or magnetization (Ms) of the nanowire. This finding may be of great importance for the design of microwave oscillator with stable and accurate frequency.

Patterned arrays of micron and submicron rectangular Ni81Fe19 elements studied by ferromagnetic resonance (FMR) previously showed that an in-plane shape anisotropy existed in the element, with two origins. One is contributed from a quasiuniform magnetization described by conventional demagnetizing factors, another is an effect of the non-uniform magnetization in the nonellipsoidal element. The results of micromagnetic numerical calculation provide further evidence of the nonuniform demagnetizing field and nonuniform magnetization in the rectangular elements. The calculated profile of demagnetizing field shows that as the aspect ratio increases the non-uniform demagnetizing field decreases, as the data of in-plane FMR require. When the static field is not along either of the edges the demagnetizing field become more nonuniform. Not only its magnitude but also its direction is nonuniform, which causes nonuniform static and microwave field and thus meets the condition for magnetostatic mode excitation as obs...

Magneto-transport properties have been systematically studied in Cu-wedge regular and specular spin valves prepared by magnetron sputtering. In the specular spin valve, a thin oxide layer is inserted between the Ta underlayer and the free layer to provide a specular interface. Up to 50% enhancement in giant magnetoresistance (GMR) is realized by the specular interface at room temperature. The observed Cu layer thickness dependence of both the resistivity and GMR in both types of the spin valves has been satisfactorily modeled using a semiclassical Boltzmann approach. Temperature dependence of the GMR has been measured from 325 to 15 K for several Cu-layer thicknesses. The specular scattering enhancement initially increases as the temperature is lowered from 325 K, but rapidly decreases below 100 K. This decrease is correlated with the reduced degree of the full antiparallel alignment between the magnetic moments of the pinned and free layers in the specular spin valve, which is caused by the antiferromagn...

We demonstrate a design of two-dimensional density-near-zero (DNZ) membrane structure to control sound transmission. The membrane structure is theoretically modeled as a network of inductors and capacitors, and the retrieved effective mass density is confirmed to be close to zero at the resonance frequency. This scheme proposes a convenient way to construct the unit cell for achieving DNZ at the designed frequency. Further simulations clearly demonstrate that the membrane-network has the ability to control sound transmission such as achieving cloaking, high transmission through sharp corners, and high-efficient wave splitting. Different from the phononic-crystal-based DNZ materials, the compact DNZ membrane-network is in deep subwavelength scale and provides a strong candidate for acoustic functional devices.

We studied the magnetothermopower of Co/Cu1−xNix multilayers (with x=0.37 and 0.42) at various temperatures. Both systems have negative thermopower and the magnitude of the thermopower increases as the magnetic field increases. We found that as the ferromagnetic component of the magnetization becomes larger at lower temperatures, both the magnetothermopower and the magnetoresistance decrease. The inverse relationship between the thermopower and the resistance, when the field H varies, holds well at different temperatures. We interpret the results in terms of the two‐current model, with an emphasis on the spin‐split density of states.

Low visible light absorption and high charge carrier recombination rate are two main disadvantages of TiO2 as a photocatalyst which severely limit its practical applications. To overcome the problems, Fe mono-doped and (Fe+Mo) co-doped TiO2 were synthesized and studied. It was found that (Fe+Mo) co-doping can further increase the visible absorption and improve the photocatalytic property of TiO2 compared with Fe mono-doping; Fe mono-doping improves the photocatalytic property of TiO2 only at very low doping level (Fe concentration less than 1.0%), while by co-doping a small amount of Mo with Fe, the effective doping concentration of Fe can be pushed to a higher level and the photocatalytic property of TiO2 can be further improved. Photoluminescence spectra indicated that Mo dopant may play a role in retarding the recombination process when co-doped into TiO2 with Fe. The mechanism behind was discussed. It was suggested that doping a small amount of Mo into Fe-TiO2 might be an efficient way to further improve the photocatalytic property of Fe-TiO2 without losing its photocatalytic specificity.

Perovskite ferroelectricceramics of ( 1 − x ) BaTiO 3 – x ( K 1 / 4 Bi 3 / 4 ) ( Mg 1 / 4 Ti 3 / 4 ) O 3 [ ( 1 − x ) BT – x KBMT , x = 0.06 , 0.1, and 0.14] were synthesized via solid-state reaction method. Dielectric constant maximum e m of BT-KBMT ceramics declines with KBMT content. e ( T ) peak temperature T m (402 K) is close to T c (403 K) of the parent BT for composition 0.94BT-0.06KBMT, and decreases to 382 K for 0.9BT-0.1KBMT. Dielectric behaviors of the two compositions exhibit features of ferroelectrics with diffuse phase transition. A high-field linear polarization behavior was observed in the two compositions around temperature range of the e ( T ) peak summit. e ( T ) peak of 0.86BT-0.14KBMT is saddle-backed. The high turning temperature T m 1 fixes around 384 K, and is the Burns temperature T B of the composition. The low turning point T m 2 is 326 K at 100 Hz and highly frequency dependent. The dielectric anomaly of 0.86BT-0.14KBMT around T m 2 is associated with diffuse transitions from ferroelectric macrodomains to microdomains, polar nanoregions and paraelectric states.

Cobalt ferrite nanoparticles were synthesized via the hydrothermal route with the addition of trisodium citrate dihydrate (Na(3)CA center dot 2H(2)O). The characterizations including x-ray diffraction (XRD) and transmission electron microscope showed that the products of this hydrothermal reaction are composed of cobalt ferrite nanocrystallite and a small amount of FeOOH, and the average crystallite size of the nanoparticles is 7.6 +/- 0.3 nm by XRD. The magnetic measurements revealed the temperature-dependent magnetic properties: The superparamagnetism occurs above 380 K due to the overcoming of energy barrier for the flip of spins, which arises from the magnetocrystalline anisotropy energy and the interparticle interactions due to the aggregation of the nanoparticles; a frozen spin-glasslike state was observed below 20 K, which is accompanied with the decrease in coercivity and high-field paramagnetic susceptibility, as well as the enhancement of saturated magnetization and the effective magnetic anisotropy constant. (C) 2010 American Institute of Physics. [doi:10.1063/1.3499289]

Microstructural studies using transmission electron microscopy were performed on a ZnO:Mn diluted magnetic semiconductor thin film. The high-resolution imaging and electron diffraction reveal that the ZnO:Mn thin film has a high structural quality and is free of clustering/segregated phases. High-angle annular dark field imaging and x-ray diffraction patterns further support the absence of phase segregation in the film. Magnetotransport was studied on the ZnO:Mn samples, and from these measurements, the temperature dependence of the resistivity and magnetoresistance, electron carrier concentration, and anomalous Hall coefficient of the sample is discussed. The anomalous Hall coefficient depends on the resistivity, and from this relation, the presence of the quadratic dependence term supports the intrinsic spin-obit origin of the anomalous Hall effect in the ZnO:Mn thin film.

Diluted magnetic semiconducting ZnO:Co thin films with above room-temperature TC were prepared. Transmission electron microscopy and x-ray diffraction studies indicate the ZnO:Co thin films are free of secondary phases. The magnetization of the ZnO:Co thin films shows a free electron carrier concentration dependence, which increases dramatically when the free electron carrier concentration exceeds ∼1019 cm−3, indicating a carrier-mediated mechanism for ferromagnetism. The anomalous Hall effect is observed in the ZnO:Co thin films. The anomalous Hall coefficient and its dependence on longitudinal resistivity were analyzed. The presence of a side-jump contribution further supports an intrinsic origin for ferromagnetism in ZnO:Co thin films. These observations together with the magnetic anisotropy and magnetoresistance results support an intrinsic carrier-mediated mechanism for ferromagnetic exchange in ZnO:Co diluted magnetic semiconductor materials.

We measured acoustic transmissions through subwavelength hole arrays fabricated on brass plates at normal and oblique incidence. It is found experimentally that the transmission phenomena for the hole array in thin plate case are analogous to the previously observed enhanced transmission of electromagnetic waves [Ebbesen et al., Nature (London) 391, 667 (1998)]. While for the hole array in thick plate case, the transmission peaks of acoustic wave occur well below Wood’s anomalies, and the spectrum characteristics reveal a Fabry–Perot-like resonance. An effective fluid approach is conceived and it can well describe the transmission properties of the hole array in thick plates within a range of incidence angle.

We have studied quasistatic magnetic switching of electron-beam patterned Ni81Fe19 (NiFe) elements over a wide range of temperatures. Switching properties depend on both lateral and thickness dimensions of the patterned structures. In large aspect-ratio elements, the switching between the two bistable states occurs through thermally activated nucleation and the switching field depends linearly on temperature. As the aspect ratio decreases, a third stable remanent state-trapped vortex state develops, but the switching fields between different states also linearly depend on temperature. As the film thickness decreases, the trapped vortex population clearly becomes thermally activated.

We have successfully demonstrated the construction of patterned magnetic nanostructures down to 50 nm dimensions using electron-beam lithography. Two types of patterned structures have been fabricated for this work: nanostructured arrays consisting of isolated identical elements and nanostructured chains of alternating elements with different widths. Small patterned arrays (∼200 μm×200 μm) have been characterized using a variable temperature (5 to 325 K) focused magneto-optic Kerr effect (MOKE) measurement system. The switching field of the isolated element arrays is found to be inversely proportional to the element width. However, as the elements of two different widths are connected to form a chain, magnetization reversal is essentially controlled by the wider constituent, indicating that the switching of chains starts in the wider elements. Domain walls in these wide elements then propagate through the narrower components, requiring a lower field than domain nucleation in the narrow elements. Magnetic ...

Submicron ferromagnets have been successfully incorporated into GaAs semiconductors by Mn+ ion implantation and subsequent heat treatment. Transmission electron microscopy, x‐ray fluorescence spectrum analysis, and atomic force microscopy are used to structurally characterize the GaMn precipitates which form within the GaAs matrix. These crystallites are room‐temperature ferromagnets with controllable magnetic properties. Magnetic force microscopy images reveal that unmagnetized samples contain both magnetic dipoles and quadrupoles, but that after magnetization the single‐domain state predominates.