Stoichiometric Cr 2 Se 3 single crystals are particular layer-structured antiferromagnets, which possess a noncollinear spin configuration, weak ferromagnetic moments, moderate magnetoresistance (MR ∼14.3%), and poor metallic conductivity below the antiferromagnetic phase transition. Here, we report an interesting >16 000% colossal magnetoresistance (CMR) effect in Ti (1.5 atomic percent) lightly doped Cr 2 Se 3 single crystals. Such a CMR is approximately 1143 times larger than that of the stoichiometric Cr 2 Se 3 crystals and is rarely observed in layered antiferromagnets and is attributed to the frustrated spin configuration. Moreover, the Ti doping not only dramatically changes the electronic conductivity of the Cr 2 Se 3 crystal from a bad metal to a semiconductor with a gap of ∼15 meV but also induces a change in the magnetic anisotropy of the Cr 2 Se 3 crystal from strong out-of-plane to weak inplane. Further, magnetotransport measurements reveal that the low-field MR scales with the square of the reduced magnetization, which is a signature of CMR materials. The layered Ti:Cr 2 Se 3 with the CMR effect could be used as two-dimensional (2D) heterostructure building blocks to provide colossal negative MR in spintronic devices.

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The magnetostatic energy of a two-dimensional (2D) periodic array of magnetic particles (or a thin film with periodic magnetization) is evaluated, including additional energy terms due to a polarizable substrate. The polarization of the substrate is solved self-consistently using surface charges. This requires describing the magnetic potential of the 2D array in terms of an equivalent surface charge distribution. Analytic expressions for the magnetostatic self-energy of the 2D array as well as the energy due to the interaction of the magnetic structure and polarizable substrate are presented. It is shown how substrates with large susceptibility significantly alter the stray-field energy and, hence, the magnetic properties of the array, even promoting a spin-reorientation transition. Our results suggest that system properties can be controlled in a simple way by exploiting substrates with tunable polarizability.