Y. T. Yang

Electric field control of magnetic properties in CoPt/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure at room temperature

We demonstrate an obvious electric-field control of magnetic properties in CoPt/PMN-PT heterostructure at room temperature. Not only the remanent magnetization but also the coercivity exhibits an obvious response with the electric field. Without the aid of magnetic bias field, the remanent magnetization of the CoPt film shows an analogous on-off behavior with the electric field switching on and off alternatively. The magnetization reversal can be electrically controlled in this heterostructure due to the variation of coercivity caused by electric field.

Electric field control of magnetism in FePd/PMN-PT heterostructure for magnetoelectric memory devices

We report a strain-mediated magnetoelectric random access memory in FePd/PMN-PT heterostructure. Due to the strong converse magnetoelectric effect, the effective anisotropy of the FePd film is controlled by the applied electric field and used to switch the magnetization from one state to the other. Taking the advantage of the large electric-field modulation of magnetic properties, the electric-write/magnetic-read memory is obtained in such heterostructure. This magnetoelectric memory provides a promising approach to the development of a practical magnetoelectric device at room temperature.

The electric field manipulation of magnetization in La1−xSrxCoO3/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructures

La1−xSrxCoO3 (xu2009=u20090.18, 0.33, and 0.5) films were grown epitaxially on piezoelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 substrates by pulsed laser deposition. The magnetization of these films varies with the external electric field, showing the magnetoelectric effect. With different doping content of Sr2+ ions, the change of magnetization for these films show different behaviors with increasing temperature, which can be attributed to the competition between electric-field-induced changes of spin state and double exchange interaction. This work presents an alternative mechanism to investigate the electric field control of magnetism in magnetoelectric heterostructure by tuning the spin state.

Electric-field-assisted magnetization switching in FePd/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure at room temperature

We demonstrate an electric-field-assisted magnetization switching in FePd/PMN-PT heterostructure at room temperature. Not only the remanent magnetization but also the coercivity exhibits an obvious response with the electric field. Without the aid of magnetic bias field, the remanent magnetization of the FePd film shows an analogous on-off behavior with the electric field switching on and off alternatively. The magnetization switching can be electrically controlled in this heterostructure due to the variation of coercivity caused by electric field.

Electrical controlled magnetism in FePt film with the coexistence of two phases

A series of FePt films with different magnetic structures are deposited on Pb(Mg1/3Nb2/3)O3–PbTiO3 substrates. By applying an electric field across the piezoelectric single crystal substrate, an magnetoelectric effect is observed in FePt/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure due to the phase transformation between face-centered cubic and face-centered tetragonal phases in the film. Taking advantage of the different coercivity caused by the electric field, the sign of magnetization can be manipulated reversibly at room temperature with the electric field switching on or off. Based on this experimental result, we demonstrate a model for the technology of information storage, in which data can be written electrically without false writing.

Electric field mediated non-volatile tuning magnetism in CoPt/PMN-PT heterostructure for magnetoelectric memory devices

We report a power efficient non-volatile magnetoelectric memory in the CoPt/(011)PMN-PT heterostructure. Two reversible and stable electric field induced coercivity states (i.e., high-HC or low-HC) are obtained due to the strain mediated converse magnetoelectric effect. The reading process of the different coercive field information written by electric fields is demonstrated by using a magnetoresistance read head. This result shows good prospects in the application of novel multiferroic devices.

Interaction between cavitation microbubble and cell: A simulation of sonoporation using boundary element method (BEM)

Sonoporation has been widely accepted as a significant tool for gene delivery as well as some bio-effects like hemolysis, bringing in high demands of looking into its underlying mechanism. A two-dimensional (2D) boundary element method (BEM) model was developed to investigate microbubble-cell interaction, especially the morphological and mechanical characteristics around the close-to-bubble point (CP) on cell membrane. Based on time evolution analysis of sonoporation, detailed information was extracted from the model for analysis, including volume expansion ratio of the bubble, areal expansion ratio of the cell, jet velocity and CP displacement. Parametric studies were carried out, revealing the influence of different ultrasound parameters (i.e., driving frequency and acoustic pressure) and geometrical configurations (i.e., bubble-cell distance and initial bubble radius). This model could become a powerful tool not only for understanding bubble-cell interactions, but also for optimizing the strategy of sonoporation, such that it could be safer and of higher efficiency for biological and medical studies especially in clinics.

Investigation into the Effect of Acoustic Radiation Force and Acoustic Streaming on Particle Patterning in Acoustic Standing Wave Fields

Acoustic standing waves have been widely used in trapping, patterning, and manipulating particles, whereas one barrier remains: the lack of understanding of force conditions on particles which mainly include acoustic radiation force (ARF) and acoustic streaming (AS). In this paper, force conditions on micrometer size polystyrene microspheres in acoustic standing wave fields were investigated. The COMSOL® Mutiphysics particle tracing module was used to numerically simulate force conditions on various particles as a function of time. The velocity of particle movement was experimentally measured using particle imaging velocimetry (PIV). Through experimental and numerical simulation, the functions of ARF and AS in trapping and patterning were analyzed. It is shown that ARF is dominant in trapping and patterning large particles while the impact of AS increases rapidly with decreasing particle size. The combination of using both ARF and AS for medium size particles can obtain different patterns with only using ARF. Findings of the present study will aid the design of acoustic-driven microfluidic devices to increase the diversity of particle patterning.

Surface-effect enhanced magneto-electric coupling in FePt/PMN-PT multiferroic heterostructures

A series of FePt films with different film thickness are deposited on Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) substrates. A standard symmetric ‘Butterfly’ shaped ΔM/M-Edc loops is obtained in 8 nm FePt/PMN-PT heterostrucuture via strain mediated magnetoelectric coupling. For the 3 nm FePt/PMN-PT heterostructure, the loop-like in-plane magnetization (M) -E curve shares a similar shape with the electric polarization of PMN-PT as a function of electric field. The value of MS shows a dramatic change of 30.9% with Edc changing from 0 to 8 kV/cm, this giant magnetoelectric effect in 3 nm FePt/PMN-PT heterostructure results from the remnant polarization induced charge on FePt/PMN-PT interface via the screening charge effect. The enhanced magnetoelectric coupling in thin magnetic/ferroelectric heterostructures opens a promising avenue for the design of ultralow power magnetoelectric devices and information storage devices.

The enhanced HIFU-induced thermal effect via magnetic ultrasound contrast agent microbubbles

High intensity focused ultrasound (HIFU) has been regarded as a promising technology for treating cancer and other severe diseases noninvasively. In the present study, dual modality magnetic ultrasound contrast agent microbubbles (MBs) were synthesized by loading the super paramagnetic iron oxide nanoparticles (SPIOs) into the albumin-shelled MBs (referred as SPIO-albumin MBs). Then, both experimental measurements and numerical simulations were performed to evaluate the ability of SPIO-albumin MBs of enhancing HIFU-induced thermal effect. The results indicated that, comparing with regular albumin-shelled MBs, the SPIO-albumin MBs would lead to quicker temperature elevation rate and higher peak temperature. This phenomenon could be explained by the changes in MBs physical and thermal properties induced by the integration of SPIOs into MB shell materials. In addition, more experimental results demonstrated that the enhancement effect on HIFU-induced temperature elevation could be further strengthened with more SPIOs combined with albumin-shell MBs. These observations suggested that more violent cavitation behaviors might be activated by ultrasound exposures with the presence of SPIOs, which in turn amplified ultrasound-stimulated thermal effect. Based on the present studies, it is reasonable to expect that, with the help of properly designed dual-modality magnetic MBs, the efficiency of HIFU-induced thermal effect could be further improved to achieve better therapeutic outcomes.