Title: Strong Magnetic Interactions and Short Range Magnetic Correlations in CuTeO4

Abstract: \ch{CuTeO4} has been proposed as a crystallographically distinct, yet electronic structure analog, of superconducting cuprates. Magnetization measurements from T = 2-300 K indicate the presence of antiferromagnetic, low dimensional correlations with J = 148(7) K. Below T $\approx$ 50 K, there is an upturn in magnetization indicative of enhanced ferromagnetic correlations, with neutron powder diffraction data showing the emergence of diffuse magnetic scattering at Q $\approx$ 0.6 \si{\angstrom^{-1}}. A Warren line shape analysis yields a characteristic magnetic correlation length of $\xi$ = 4.5(9) \si{\angstrom} at T = 40 K, rising to $\xi$ = 10.1(9) \si{\angstrom} at T = 10 K. Specific heat measurements reveal a sizable T-linear contribution of $\gamma$ = 8.3 mJ/mol-f.u/K^2 at T < 5 K. Together, these results imply a low dimensional, antiferromagnetic spin glass state. Structural modeling of the neutron powder diffraction data reveals the presence of a layered-type of stacking disorder, providing both a rationale for the lack of long range magnetic order, as well as being consistent with the computational predictions of its two-dimensional nature. Unlike the cuprates, we find no evidence of substantive dopability in this wide band-gap, yellow insulator.