Mechanical properties of macroscopic magnetocrystals

We studied experimentally and by numerical simulations the mechanical response of arrays of macroscopic magnetic spheres when an external stress is applied. First, the tensile strength of single chains and ribbons was analyzed. Then, simple cubic (cP), hexagonal (Hx) and hybrid (cP-Hx) structures, called here magnetocrystals, were assembled and subjected to tensile stress, bending stress and torsion until failure was reached. Atomistic crystalline structures are isotropic, but in the case of magnetocrystals, even when geometric isotropy is obeyed, dipolar magnetic interactions introduce a physical anisotropy which modifies, in a non-usual manner, the structures response to the kind of external stress applied. For instance, cP and Hx magnetocrystals subjected to tension exhibit a behavior akin to a brittle and ductile failure, respectively, but under bending the cP structure becomes ductile while the hexagonal lattice becomes brittle. For the hybrid structure, its elastic response and strength are enhanced or reduced depending on which crystallographic direction the stress is applied. These properties, so far unexplored, give to crystalline magnetic arrays a potential interest in the design of metama-terials.