Abstract
Fe–Cu films with pseudo‐ordered, hierarchical porosity are prepared by a simple, two‐step procedure that combines colloidal templating (using sub‐micrometer‐sized polystyrene spheres) with electrodeposition. The porosity degree of these films, estimated by ellipsometry measurements, is as high as 65%. The resulting magnetic properties can be controlled at room temperature using an applied electric field generated through an electric double layer in an anhydrous electrolyte. This material shows a remarkable 25% voltage‐driven coercivity reduction upon application of negative voltages, with excellent reversibility when a positive voltage is applied, and a short recovery time. The pronounced reduction of coercivity is mainly ascribed to electrostatic charge accumulation at the surface of the porous alloy, which occurs over a large fraction of the electrodeposited material due to its high surface‐area‐to‐volume ratio. The emergence of a hierarchical porosity is found to be crucial because it promotes the infiltration of the electrolyte into the structure of the film. The observed effects make this material a promising candidate to boost energy efficiency in magnetoelectrically actuated devices.
Highlights
Introduction efficiency in magnetically actuated devicesVoltage control of magnetism can be achieved through several mechanisms
This result from ellipsometry can be further supported by high magnification field emission scanning electron microscope (FESEM) images which reveal the existence of disperse nanopores
Iron has four unpaired 3d electrons with a high density of states near the Porous, pseudo-ordered thin metallic films consisting of nontoxic, abundant elements and prepared using a simple, reproducible and environmentally friendly process have been fabricated
Summary
The electroplated continuous film contained about a 33% volume fraction of air compared to the sputtered reference sample This result from ellipsometry can be further supported by high magnification FESEM images (not shown) which reveal the existence of disperse nanopores. Approximated depth profiles of air within the films are shown in Figure 3b for a simple description of the layer as two sublayers with different void fractions (see the Experimental Section for details) In this graph, the zero in the X-axis corresponds to the substrate, and the curves extend through the depth of the film until the total thickness is reached (where each horizontal line finishes abruptly), marking the surface with air. The reflectivity becomes lower with increasing pore size, as the refractive index decreases (reducing index contrast with air) and scattering increases due to pore dimensions which become comparable to the wavelength of light
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