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We report our studies of the thickness dependence of electrical resistivity and lattice constants in strained epitaxial thin films of calcium manganese oxide. Our results indicate the potential of bi-axial lattice mismatch strain as a handle for modulating electrical resistivity. We observe thickness dependence of lattice constants consistent with what is expected for strain relaxation for films thicker than 400 Å. At lower thickness values, anomalies are observed suggestive of reduced oxygen stoichiometry. We observe a remarkable decrease in electrical resistivity with decreasing film thickness. The resistivity of our thinnest films (5–7 nm) is about three orders of magnitude lower than the resistivity of bulk CaMnO3. Resistivity increases as the film thickness increases, along with the progression of strain relaxation. It is noteworthy that the thickness dependence of resistivity we observe in CMO thin films is the opposite of what has been reported for their hole-doped rare earth manganite counterpart La0.67Ca0.33MnO3 (LCMO), where tensile lattice mismatch strain suppresses metallicity, leading to the increase in resistivity with film thickness. We believe that the enhanced conductivity in our thinnest films is related to the possible oxygen deficiency promoted by tensile strain. Recent x-ray absorption measurements have revealed reduced oxygen content and associated changes in Mn valence states in tensile-strained CMO thin films, as also predicted by density functional theory calculations. This report is the first observation of electrical transport behavior possibly indicative of strain–oxygen stoichiometry coupling. 

We apply the density-functional theory to study various phases (including non-magnetic (NM), anti-ferromagnetic (AFM), and ferromagnetic (FM)) in monolayer magnetic chromium triiodide (CrI 3 ), a recently fabricated 2D magnetic material. It is found that: (1) the introduction of magnetism in monolayer CrI 3 gives rise to metal-to-semiconductor transition; (2) the electronic band topologies as well as the nature of direct and indirect band gaps in either AFM or FM phases exhibit delicate dependence on the magnetic ordering and spin–orbit coupling; and (3) the phonon modes involving Cr atoms are particularly sensitive to the magnetic ordering, highlighting distinct spin–lattice and spin–phonon coupling in this magnet. First-principles simulations of the Raman spectra demonstrate that both frequencies and intensities of the Raman peaks strongly depend on the magnetic ordering. The polarization dependent A 1g modes at 77 cm −1 and 130 cm −1 along with the E g mode at about 50 cm −1 in the FM phase may offer a useful fingerprint to characterize this material. Our results not only provide a detailed guiding map for experimental characterization of CrI 3 , but also reveal how the evolution of magnetism can be tracked by its lattice dynamics and Raman response.