Magnetism of the antiferromagnetic spin-$frac{1}{2}$ tetramer compound CuInVO$_5$

We measured the temperature dependence of the magnetic susceptibility and specific heat and the magnetic-field dependence of the magnetization of CuInVO$_5$. An antiferromagnetically ordered state appears below $T_{rm N} = 2.7$ K. We observed a $frac{1}{2}$ quantum magnetization plateau above 30 T at 1.3 K. We show that the spin system consists of antiferromagnetic spin-$frac{1}{2}$ tetramers with $J_1 = 240 pm 20$ and $J_2 = -142 pm 10$ K for the intratetramer interactions.