Magnetic properties of ${\mathrm{Nd}}_2$${\mathrm{CuO}}_4$-type ${\mathit{R}}_2$${\mathrm{CuO}}_4$ (R=Y, Dy, Ho, Er, Tm) synthesized under high pressure: Weak ferromagnetism of ${\mathrm{Y}}_2$${\mathrm{CuO}}_4$

Magnetization of ${\mathit{R}}_2$ ${\mathrm{CuO}}_4$ (R=Y, Dy, Ho, Er, Tm) crystallizing in the ${\mathrm{Nd}}_2$ ${\mathrm{CuO}}_4$-type (T’) structure has been measured between 4 and 300 K. In ${\mathrm{Y}}_2$ ${\mathrm{CuO}}_4$ antiferromagnetic ordering of ${\mathrm{Cu}}^{2+}$ spins at 260 K has been detected clearly, without being interfered with by the paramagnetic contribution of rare-earth elements as in the other compositions. Weak ferromagnetic behavior with a moment of 9×${10}^{\mathrm{-}4}$ ${\mathrm{\mu }}_{\mathit{B}}$/Cu accompanies the antiferromagnetic transition. ${\mathrm{Dy}}^{3+}$, ${\mathrm{Ho}}^{3+}$, ${\mathrm{Er}}^{3+}$, and ${\mathrm{Tm}}^{3+}$ ions obey the Curie-Weiss law at relatively high temperatures, and the effective moments are in good agreement with the values anticipated from their lowest multiplet levels. Various types of deviations from the law occur at low temperatures. Specifically, a sharp kink possibly suggesting antiferromagnetic ordering of the ${\mathrm{Dy}}^{3+}$ moments has been found at 7 K. Anomalies around 200 K for ${\mathrm{Ho}}_2$ ${\mathrm{CuO}}_4$ and ${\mathrm{Er}}_2$ ${\mathrm{CuO}}_4$ reflect the weak ferromagnetic contribution of the ${\mathrm{CuO}}_2$ lattice.