A substrate having an arrangement of self-assembling magnetic domains and a method of fabrication therefor. In some embodiments, a substrate is patterned with a plurality of chemically contrasted alignment features, and a block copolymer having a magnetic component and a non-magnetic component is deposited onto the substrate. The block copolymer self-assembles into a sequence of magnetic domains responsive to the alignment features. The period of the alignment features is between about 2 times and about 10 times the period of the magnetic domains.