We study the effect of sputter-deposition conditions, namely, substrate temperature and chamber base pressure, upon the interface quality of epitaxial Pt/Co/Pt thin films with perpendicular magnetic anisotropy. Here we define interface quality to be the inverse of the sum in quadrature of roughness and intermixing. We find that samples with the top Co/Pt layers grown at 250• C exhibit a local maximum in roughness intermixing and that the interface quality is better for lower or higher deposition temperatures, up to 400• C, above which the interface quality degrades. Imaging the expansion of magnetic domains in an in-plane field using wide-field Kerr microscopy, we determine the interfacial Dzyaloshinskii-Moriya interaction (DMI) in films in the deposition temperature range 100• C to 300• C. We find that the net DMI increases as the difference between top and bottom Co interface quality increases. Furthermore, for sufficiently low base pressures, the net DMI increases linearly with the deposition temperature, indicating that fine-tuning of the DMI may be achieved via the deposition conditions.

The perpendicular magnetic anisotropy Keff, magnetization reversal, and field-driven domain wall velocity in the creep regime are modified in Pt/Co(0.85–1.0 nm)/Pt thin films by strain applied via piezoelectric transducers. Keff, measured by the extraordinary Hall effect, is reduced by 10 kJ/m3 by tensile strain out-of-plane εz = 9 × 10−4, independently of the film thickness, indicating a dominant volume contribution to the magnetostriction. The same strain reduces the coercive field by 2–4 Oe, and increases the domain wall velocity measured by wide-field Kerr microscopy by 30-100%, with larger changes observed for thicker Co layers. We consider how strain-induced changes in the perpendicular magnetic anisotropy can modify the coercive field and domain wall velocity.

We have imaged Néel skyrmion bubbles in perpendicularly magnetised polycrystalline multilayers patterned into 1 µm diameter dots, using scanning transmission x-ray microscopy. The skyrmion bubbles can be nucleated by the application of an external magnetic field and are stable at zero field with a diameter of 260 nm. Applying an out of plane field that opposes the magnetisation of the skyrmion bubble core moment applies pressure to the bubble and gradually compresses it to a diameter of approximately 100 nm. On removing the field the skyrmion bubble returns to its original diameter via a hysteretic pathway where most of the expansion occurs in a single abrupt step. This contradicts analytical models of homogeneous materials in which the skyrmion compression and expansion are reversible. Micromagnetic simulations incorporating disorder can explain this behaviour using an effective thickness modulation between 10 nm grains.

The interfacial Dzyaloshinskii-Moriya interaction (DMI) has been shown to stabilize homochiral Néel-type domain walls in thin films with perpendicular magnetic anisotropy and as a result permit them to be propagated by a spin Hall torque. In this study, we demonstrate that in Ta/Co 20 Fe 60 B 20 /MgO the DMI may be influenced by annealing. We find that the DMI peaks at D = 0.057 ± 0.003 mJ/m 2 at an annealing temperature of 230 • C. DMI fields were measured using a purely field-driven creep regime domain expansion technique. The DMI field and the anisotropy field follow a similar trend as a function of annealing temperature. We infer that the behavior of the DMI and the anisotropy are related to interfacial crystal ordering and B expulsion out of the CoFeB layer as the annealing temperature is increased.

We study the magnetic properties of perpendicularly magnetized Pt/Co/Ir thin films and investigate the domain-wall creep method of determining the interfacial Dzyaloshinskii-Moriya (DM) interaction in ultrathin films. Measurements of the Co layer thickness dependence of saturation magnetization, perpendicular magnetic anisotropy, and symmetric and antisymmetric (i.e., DM) exchange energies in Pt/Co/Ir thin films have been made to determine the relationship between these properties. We discuss the measurement of the DM interaction by the expansion of a reverse domain in the domain-wall creep regime. We show how the creep parameters behave as a function of in-plane bias field and discuss the effects of domain-wall roughness on the measurement of the DM interaction by domain expansion. Whereas modifications to the creep law with DM field and in-plane bias fields have taken into account changes in the energy barrier scaling parameter α, we find that both α and the velocity scaling parameter v 0 change as a function of in-plane bias field.

We demonstrate a Josephson junction with a weak link containing two ferromagnets, with perpendicular magnetic anisotropy and independent switching fields in which the critical current can be set by the mutual orientation of the two layers. Such pseudospin-valve Josephson junctions are a candidate cryogenic memory in an all superconducting computational scheme. Here, we use Pt/Co/Pt/CoB/Pt as the weak link of the junction with d Co = 0.6 nm, d CoB = 0.3 nm, and d Pt = 5 nm and obtain a 60% change in the critical current for the two magnetization configurations of the pseudospin-valve. Ferromagnets with perpendicular magnetic anisotropy have advantages over magnetization in-plane systems which have been exclusively considered to this point, as in principle the magnetization and magnetic switching of layers in the junction should not affect the in-plane magnetic flux.Josephson junctions containing ferromagnetic weak links have been of interest over the last twenty years due to the additional physics present when pair correlations from the superconductor (S) interact with the exchange field of the ferromagnet (F) 1-5 . Examples include the tuning of the ground state phase difference across a junction from 0 to π by changing the thickness of the F layer 6-9 . The additional physics can also drive the generation of m s = ±1 spin-triplet pair correlations with spin projection along the magnetization axis of the F layer in the junction 10 , leading to pair propagation through the F layer over much longer distances than the singlet component [11][12][13][14][15][16][17]

It is demonstrated that the dielectric permittivity and piezoelectric coefficients in relaxor-PbTiO3 single crystals close to the morphotropic phase boundary (MPB) can be augmented by contributions from domain walls. Landau-Ginzburg-Devonshire models, incorporating both polarization and strain gradients through the domain walls, show that wall contributions in domain engineered single crystals originate from enhanced, field-induced polarization rotation in static domain walls, unlike ceramics, in which piezoelectricity is enhanced by domain wall translation. For 71° domain walls in 0.7 Pb(Mg1/3Nb2/3)O3 -0.3PbTiO3 the piezoelectric charge coefficient d33 at the center of the wall ranges from 5000 to >30,000 pC N -1 depending on the wall width. Thus, a sufficiently high domain wall density can account for the experimentally observed augmentation in the measured properties compared to single domain models. The symmetry of the domain walls explains both the variety of average symmetries observed close to the MPB and the experimentally observed switching of the [001]-oriented crystals into the tetragonal phase via a symmetry-improbable MC phase. For a crystal of rhombohedral ground state, the presence of domain walls will impart monoclinic symmetry, the predominance of which increases with increasing domain wall density.

We study the energy and creep velocity of magnetic domain walls in perpendicularly magnetised Pt/Co/Ir thin films under strain. We find that the enhancement of domain wall creep velocity under strain from piezoelectric transducers is largest in films with the thinnest Co layers (0.56 nm), in which the strain causes the smallest relative change in perpendicular magnetic anisotropy and the largest relative change in domain wall creep velocity. We show how domain wall energy is predictive of the sensitivity of domain wall creep velocity to changes in strain, and thus provide a route to designing magnetic thin film systems for optimum strain control.