Nanomaterials

Nanostructure Simulations

Theoretical model of a grain boundary defect in magnesium oxide.

This image shows a theoretical model of a grain boundary defect in magnesium oxide. The open channels formed at the interface between the grains are predicted to act as electron traps (cross-section of the trapped electron density is depicted by the isosurface in the figure). This novel effect is a result of the materials negative electron affinity and has important consequences for applications of MgO in nanoelectronic devices.

Magnetisation reversal in magnetic films

The experiments show a rapid demagnetisation and recovery followed by a slow evolution of the magnetisation into the field direction, suggesting the existence of two characteristic relaxation times: the longitudinal and transvers relaxation times.

Thermally assisted ultrafast magnetisation reversal in magnetic films has been investigated in the femtosecond time domain. The experiments show a rapid demagnetisation and recovery followed by a slow evolution of the magnetisation into the field direction, suggesting the existence of two characteristic relaxation times: the longitudinal and transvers relaxation times.

Hard-Soft Matter Interfaces

Microstructure of parts of the coral skeleton (Porites lobata) as visualized by optical
(A) and electron microscopy (B).. A

The combination of hard (organic) and soft (mineral) materials leads to the formation of composites with often superior properties to those of the separate components. Nature uses this in a plethora of biomineralising systems such as scleractinian corals, bones and teeth. Our research investigates the structure and composition of these to enable the development of novel environmentally friendly bio-inspired composite materials.

Structure and Dynamical Properties

The figure shows a snapshot of a two-phase coexistence calculation of melting

Recent research includes the application of the Path Integral Molecular Dynamics (PIMD) technique to study the phase diagram of hydrogen, including the solid:solid transitions and the melting transition at high pressure. The figure shows a snapshot of a two-phase coexistence calculation of melting and was published in Nature Communications (2013).

Computational Magnetism


‌‌The York computational magnetism group is at the forefront of the development of theoretical and computational approaches to the properties of magnetic materials and their applications, which include magnetic recording and an expanding interest in biomagnetism.‌


 

Nanoparticle Catalysis Research

Atomic Columns

Aberration corrected environmental electron microscopy is used to analyse the structures of catalytically active materials with sub-Angstrom precision.  The image of atomic columns introduces a new radial lattice expansion explanation for the surprisingly high catalytic activity of 2-4nm multiply twinned gold nanoparticles for low temperature CO oxidation in fuel cell applications.

Magnetisation Dynamics in Hybrid Multiferroics

Magnetisation Dynamics in Hybrid Multiferroics

‌‌We have demonstrated voltage induced non-volatile switching of the magnetization in a Fe81Ga19 / PZT hybrid multiferroic device. Switching is achieved by the modification of the magnetic anisotropy by the voltage induced strain from the piezoelectric layer. Epitaxial Fe81Ga19 is shown to possess the favourable combination of cubic magnetic anisotropy and large magnetostriction necessary to achieve this functionality. The figure shows that the switching of the magnetization proceeds by the motion of magnetic domain walls (Applied Physics Letters 2012).

Functional Nanoparticles

Strain-enhanced ionic conduction

Cs corrected scanning transmission electron microscopy reveals the strain associated with the oxidation of iron nanoparticles as depicted in this figure overlaying a colour coded atomically resolved STEM micrograph and the atomic-level strain map derived from it (Nature Materials 2013).

Magnetic Materials Research

Magnetic materials research group

The clear highlight of our research in the last five years has been the development and recognition of what is known as the York Model of Exchange Bias. The model has resolved a 50 year old mystery and produced the first predictive theory of values of exchange bias. The figures show that the theoretical calculations are capable of predicting the variation of exchange bias with film thickness and grain size in polycrystalline thin films of antiferromagnets. The model is utilised by all major recording head manufacturers for whom we undertake contract measurements. The model is now being extended into other areas associated with small elements and nanowires for domain wall memories.