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Tuning the Dzyaloshinskii-Moriya interaction (DMI) using electric (E)-fields in magnetic devices has opened up new perspectives for controlling the stabilization of chiral spin structures. Recent efforts have used voltage-induced charge redistribution at magnetic/oxides interfaces to modulate the DMI. This approach is attractive for active devices but tends to be volatile, making it energy-demanding. Here we demonstrate nonvolatile E-field manipulation of the DMI by ionic-liquid gating of Pt/Co/HfO2 ultra thin films. The E-field effect on the DMI is linked to the migration of oxygen species from the HfO2 layer into the Co and Pt layers and subsequent anchoring. This effect permanently changes the properties of the material, showing that E-fields can be used not only for local gating in devices but also as a material design tool for post growth tuning of the DMI.

We report the generation of skyrmions under the combined influence of applied perpendicular magnetic fields and electrical currents in Pt/Co/Os/Pt thin films. Under no electrical current, skyrmions are found to nucleate at specific defect sites distributed throughout the film and remain pinned at these sites for small dc electrical currents $(l0.05\mathrm{MA}/\mathrm{c}{\mathrm{m}}^{2})$ . For larger currents $(l0.05\mathrm{MA}/\mathrm{c}{\mathrm{m}}^{2})$, skyrmions can either move or elongate in the direction of the current flow to form stripe domains. We further observed the current-induced generation of skyrmions through two specific processes: (i) stripe domains depinning from defect sites and collapsing into skyrmions, or (ii) skyrmions breaking off from pinned stripes; the rate of these stripe-to-skyrmion creation phenomena is proportional to the applied current density. Additionally, we observe a sudden increase in the skyrmion population immediately after the applied current is removed----a behavior attributed to stripe domains previously elongated by the electrical current collapsing back into skyrmions.

International audience; The possibility to tune the Dzyaloshinskii Moriya interaction (DMI) by electric (E) field gating in ultra-thin magnetic materials has opened new perspectives in terms of controlling the stabilization of chiral spin structures. Most recent efforts have used voltage-induced charge redistribution at the interface between a metal and an oxide to modulate DMI. This approach is attractive for active devices but it tends to be volatile, making it energy demanding, and it is limited by Coulomb screening in the metal. Here we have demonstrated the non-volatile E-field manipulation of DMI by ionic liquid gating of Pt/Co/HfO2 ultra-thin films. The E-field effect on DMI scales with the E-field exposure time and is proposed to be linked to the migration and subsequent anchoring of oxygen species from the HfO2 layer into the Co and Pt layers. This effect permanently changes the properties of the material showing that E-fields can not only be used for local gating in devices but also as a highly scalable materials design tool for post-growth tuning of DMI.

We demonstrate deterministic control of dipole-field-stabilized skyrmions by means of spin-orbit torques arising from heavy transition-metal seed layers. Experiments are performed on amorphous Fe/Gd multilayers that are patterned into wires and exhibit stripe domains and dipole skyrmions at room temperature. We show that while the domain walls and skyrmions are achiral on average due to lack of Dzyaloshinskii-Moriya interactions, the N\'eel-like closure domain walls at each surface are chiral and can couple to spin-orbit torques. The current-induced domain evolutions are reported for different magnetic phases, including disordered stripe domains, coexisting stripes and dipole skyrmions and a closed packed dipole skyrmion lattice. The magnetic textures exhibit motion under current excitations with a current density ~10^8 A/m2. By comparing the motion resulting from magnetic spin textures in Fe/Gd films with different heavy transition-metal interfaces, we confirm spin currents can be used to manipulate achiral dipole skyrmions via spin-orbit torques., Comment: 23 pages, 8 figures

The effects of mesoscale confinement on the metamagnetic behavior of lithographically patterned FeRh structures are investigated via Kerr microscopy. Combining the temperature- and field-dependent magnetization reversal of individual sub-micron FeRh structures provides specific phase-transition characteristics of single mesoscale objects. Relaxation of the epitaxial strain caused by patterning lowers the metamagnetic phase transition temperature by more than 15 K upon confining FeRh films below 500 nm in one lateral dimension. We also observe that the phase transition becomes highly asymmetric when comparing the cooling and heating cycles for 300 nm-wide FeRh structures. The investigation of FeRh under lateral confinement provides an interesting platform to explore emergent metamagnetic phenomena arising from the interplay of the structural, magnetic and electronic degrees of freedom at the mesoscopic length scale.

Rare earth elements (REEs) are highly valuable due to the complex nature of their extraction from primary and secondary sources. A key feature is that REEs often co-occur with uranium and thorium which, being radioactive, increase the hazard and complexity of REE recovery. A bioprocess which utilizes enzymatically-generated inorganic phosphate to precipitate REEs from solution as their phosphate biominerals is highly effective in the recovery of REEs, effecting rapid recovery onto immobilized bacterial biofilm at high flow-through rates. This also bioprecipitates U and Th. The metal recovery process requires addition of an organic phosphate substrate, e.g. glycerol 2-phosphate (G2P), the cleavage of which provides the inorganic phosphate source for REE biomineralization. G2P is expensive, precluding its large scale use, but early work using uranium showed that tributyl phosphate (TBP) can be used as an alternative phosphate donor molecule. The potential for substitution of G2P by TBP for biorecovery of neodymium is described and a new approach is proposed for enhancing the metal selectivity for REEs against uranium.

Batch-grown cells and a continuously-grown biofilm of a Serratia sp. were utilized to recover the rare earth elements (REEs) lanthanum and neodymium from solution. Selectivity was obtained for La(III) over Th(IV) using columns of polyacrylamide gel-immobilized cells challenged at a rapid flow rate, exploiting the different solution chemistries and behaviors of REEs(III) and Th(IV). Biofilm-grown cells had a ten-fold higher activity of mediating phosphatase, which promotes metal deposition as the corresponding metal phosphate, reflected as a correspondingly enhanced level of removal of Nd(III) (as NdPO4) in flow-through columns utilizing the biofilm on reticulated foam. The biofilms retained activity in the removal of Nd(III) for >1 year, losing activity exponentially with a half life of 3 months. The flow rate giving 50% removal (FA1/2) of Nd(III) by 3 month old biofilms at pH 5.5 was 272 and 275 mL h−1 using two independent biofilm preparations, equivalent to a FA1/2 of 34 column volumes per h for fresh biofilms. The removal of Nd(III) was sustained at pH values down to 3.5 with approx. 20% of the column activity lost upon return to pH 5.5. A similar result occurred in the presence of the common REE leaching agent ammonium sulfate (100 mM), but this did not affect the ability of Serratia sp. to recover REEs. With a view to the potential for future biomanufacturing of Nd(III)-catalysts, the deposited material was identified as NdPO4 by X-ray powder diffraction with a nanoparticle size of 14.5 nm, irrespective of the biofilm age.

International audience; We demonstrate the ability to create, control the propagation, and annihilate domain walls in 25-nm thick Tb22Co78 ferrimagnetic alloy wires using a temperature gradient under a constant appliedfield. The temperature gradient is generated by passing a current through the wire, and the domainwall properties are imaged using Kerr microscopy. The manipulation of the domain wall is madepossible by creating a temperature gradient such that the temperature at one end of the wire isabove the compensation temperature for the TbCo alloy, while the other end remains below thecompensation temperature. By tuning the intensity of the applied magnetic field and the currentflowing inside the wire, it is possible to carefully control the domain wall position that can then bestabilized under zero applied field and current.

Recently, the manipulation of domain walls using magnetic field [1] spin polarized current [2] electric field [3] and temperature gradient [4] have attracted significant interest. This control of domain wall nucleation and propagation could lead to new advances in the field of data storage [5] and magnetic logic [6]. Here we report on the use of a thermal gradient to nucleate, propagate and annihilate well-defined domain walls. The domain walls are created in lithographically patterned wires of amorphous, ferrimagnetic CoTb alloy thin films. The net magnetization of these films is defined by the competition between the magnetization of the antiferromagnetically coupled Co sublattice and Tb sublattice. For some compositions, there exists a given temperature known as the compensation temperature (T comp ), where the net saturation magnetization of the sample is zero due to the equal magnitude and opposite direction of the two competing sublattice moments. Below T comp , the net magnetization of the film aligns along the dominant Tb magnetization, while above T comp the direction of the magnetization is controlled by the Co sublattice. By crossing this compensation temperature under applied field, it is possible to change the dominant sublattice — creating a shift in the net magnetization direction of the film.

Biofilm-immobilised Citrobacter sp. removed uranyl ion from flows supplemented with glycerol 2-phosphate. The metal uptake mechanism was mediated by the activity of a cell-surface bound phosphatase that precipitated liberated inorganic phosphate with uranyl ion as HUO 2 PO 4 .4H 2 O at the bacterial surface. A modified integrated form of the Michaelis-Menten equation is proposed to describe the removal of metal ion by a columnar bioreactor, where the efficiency of metal removal is semi-quantitatively related to the input flow rate, the total enzyme loading (E 0 ) and the bioreactor activity. With biofilm immobilised bacteria, E 0 was further divisible (split) into subparameters of phosphatase titre per bacterium and total biomass surface area. Varying the split E 0 and the reaction temperature modified the bioreactor performance. The immobilised bacteria retained high metal loads without loss in steady-state activity. Accumulated metal was recovered as a concentrated solution