Molecular dynamics simulations are used to investigate the structural properties of a two-dimensional ensemble of magnetic rods, which are modeled as aligned single dipolar beads. The obtained self-assembled configurations can be characterized as (1) clusters, (2) percolated, and (3) ordered structures, and their structural properties are investigated in detail. By increasing the aspect ratio of the magnetic rods, we show that the percolation transition is suppressed due to the reduced mobility of the rods in two dimensions. Such a behavior is opposite to the one observed in three dimensions. A magnetic bulk phase is found with local ferromagnetic order and an unusual nonmonotonic behavior of the nematic order is observed.

We investigate the transport of active matter in the presence of a disordered square lattice of asymmetric obstacles, which is built by removing a fraction of them from the initial full lattice. We consider no external field. We observe a spontaneous inversion of the net particle current, compared to the usual sense of such a current reported in the literature, if the obstacle (half-circle) has the same diameter of the unit cell of the square lattice. If this diameter is smaller, there is no inversion. We show a calculation that reproduces our numerical results, based on the argument that such effects are a consequence of the imbalance of particles traveling in the positive and the negative directions due to traps formed by the obstacles: for positive travelers the traps are the spaces between neighboring obstacles, while for negative travelers, they are the flat side of the obstacles. PACS numbers: 87.80.Fe, 47.63.Gd, 87.15.hj, 05.40.-a f -0.02 0 0.02 0.04 0.06 0.08 J J x -φ = 0.732 J x -φ = 0.244 J y -φ = 0.732 J y -φ = 0.244 FIG. 4: The x and y components of the mean particle current, Jx and Jy, as a function of f for distinct values of the area fraction φ. We consider wedges as obstacles. The aperture angle of the wedges is 90 • .

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