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Banner image: False-colour cross-sectional TEM images of LcmO–ZnO nanostructures in low magnification.  (Thomas Fix; Eun-Mi Choi; Jason W. A. Robinson; Shin Buhm Lee; Aiping Chen; Bhagwati Prasad; Haiyan Wang; Mark G. Blamire; Judith L. MacManus-Driscoll; Nano Lett.  2013, 13, 5886-5890.)

 

The ability to control interacting degrees of freedom in materials that may be combined in different geometrical arrangements opens up a wide range of functionalities for applications. One may thus use a magnetic field, electric field, stress field or temperature change to control any of the conjugate variables, and vice versa. 

Electrocalorics

Applying a voltage across a ferroelectric material can switch ferroelectric domains below the Curie temperature, but near the Curie temperature an applied voltage can drive the ferroelectric phase transition itself. Driving and undriving such phase transitions produces large thermal changes known as electrocaloric effects, and these could be exploited for low‑power cooling applications. Here we study a range of electrocaloric materials, using a range of measurement protocols, in this rapidly growing area.

The image to the right shows the energy efficiency η (described as the heat transferred Q divided by the external work W) for electrocaloric (EC), magnetocaloric (MC) and mechanocaloric (mC) effects. [After Nature Physics 11 (2015) 202].

 

Magnetoelectrics

Magnetoelectric effects arise when magnetic and electrical signals are interconverted using materials, with possible applications that include low-power data storage and magnetic-field sensing. We primarily study ferromagnetic films that experience voltage-driven strain from ferroelectric underlayers. The resulting magnetic changes are imaged using magnetic force microscopy (MFM) and photoemission electron microscopy (PEEM). This latter technique relies on x-ray magnetic circular dichroism (XMCD) to achieve magnetic contrast. 
 

The image shows magnetic domains in a manganite film whose magnetization is inhomogeneous in magnitude. Field of view has diameter 6 mm. [After Nature Materials 12 (2013) 52-58].

 
 
 
Emergent quantum phenomena at heteroepitaxial oxide interfaces​
 
The Driscoll group are interested in the new emergent quantum phenomena that occur at heteroepitaxial oxide interfaces. For instance, we can create new magnetic phases with high Curie temperatures. We are currently investigating systems which exhibit both ferroelectricity and ferro or ferrimgagnetism. We use new state-of-the art advanced PLD (so-called oxide MBE) to grow the films and we characterise them using in-situ XPS. We are also interested in new vertically aligned self assembled nanocomposite heteroepitaxial systems. Here, through careful materials selection and design and by exploiting interface strain coupling (at TB.inch-2 density interfaces), we can achieve magnetoelectric coupling with very respectable coupling coefficients at room temperature. We are developing and doing in-situ measurements of such systems to both improve the magnitude of the coupling and to create laterally ordered structures.
 
 
 

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