Light-induced changes in the coercivity ΔHc are reported for cobalt ferrite nanoparticles. These changes arise from charge transfer initiated by optical absorption near 2 eV. An insulator-to-metal transition at 170 K is an upper limit for significant ΔHc. The larger ΔHc for smaller (17 nm) particles was correlated with a distortion about the Co2+ ions at B sites, which increases the absorption probability.

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Sandwich panel structures with stiff, strong face sheets and lightweight cellular cores are widely used for weight sensitive, bending dominated loading applications. The flexural stiffness and strength of a sandwich panel is determined by the stiffness, strength, thickness, and separation of the face sheets, and by the compressive and shear stiffness and strength of the cellular core. Panel performance can be therefore optimized using cores with high specific stiffness and strength. The specific stiffness and strength

Cellular metals with stochastic cell structures (foams) [1] and related materials with periodic (lattice) cell topologies [2] have attracted significant interest because of their multifunctionality. [3] When configured as the core of a sandwich panel, they provide efficient structural load support during bending [4][5][6] while also enabling other functions such as cross flow heat exchange, [7][8][9] acoustic damping, [10,11] and impact energy absorption. [12][13][14] The earliest foams were made from easily cast alloys based upon aluminum and copper [15,16] but recent developments are leading to the emergence of materials made from steels and other higher strength alloys. [17][18][19] While foam structures with either open or closed cell topologies (and occasionally with both) are relatively easily made with a small (millimeter and even submillimeter) cell size, [20] they deform by strut bending and are therefore weak. [21] Periodic structures with lattice or honeycomb cores have been shown to offer much higher specific strengths because strut stretching dominates their response to stress. [22,23] Deshpande and Fleck [24] have shown that the specific strength of a stretch dominated lattice structure usually depends upon the specific strength of the material used to make it, the relative density and a geometric factor that measures the efficiency with which the lattice supports stress. Triangulated structures with the (tetrahedral) octet truss structure [25] (the pyramidal) lattice block arrangement of trusses, [26] and 3D kagome structures [27] are the most efficient topologies for load support. They can be fabricated by investment casting [28][29][30] and by sheet stamping/forming combined with either spot welding, [31] brazing, [32] or bonding. [33] However, it is difficult to fabricate low density versions of these structures with cell diameters below 10 mm.Small cell sizes are of interest for compact heat exchange and for impact mitigation where they then provide a more uniform deformation response. Small cell size periodic structures can be made from metal wires by laying up 2D weaves or 0/90 collinear wire arrays and brazing. [34] The mechanical response of structures made this way from stainless steels have been analyzed in compression, shear, and in bending [5] and shown to provide only slightly reduced strengths compared to optimal topologies. The best of these stainless steel structures give compressive strengths of 10-20 MPa at a density of 0.5 Mg m À3 .Here, we describe a diffusion bonding process that has been developed for making small cell size collinear lattices from Ti-6Al-4V wires of much higher specific strength than stainless steel. It is similar to a method recently proposed for the making of cellular materials from titanium coated SiC monofilaments. [35] We show that the compressive strength of these titanium structures is double that of equivalent steel structures making them well suited for situations whereTitanium sandwich panels with cellular cores of a uniform 1-5 mm diameter open c...