Magnetic Ordering and Tunable Structural Phase Transition in the Chromic Compound CuMoO4

We report the first observation of long-range magnetic order in the chromic compound CuMoO 4 at 1.75 K by means of a specific heat measurement in zero magnetic field. Magnetization measurements performed up to 57 T at 4.2 K indicate a plateau at 1/3 of the saturated magnetization consistent with a simple magnetic model of two non-interacting Cu 2+ spins and two isolated antiferromagnetic dimers ( J / k B = 26 K). A large temperature-hysteresis in the magnetic susceptibility is observed to originate from the structural phase transition and to be closely related to chromism between α-CuMoO 4 (green) and γ-CuMoO 4 (brownish-red). This discontinuous phase transition is tunable using substitutional effects in Cu 1- x Zn x MoO 4 (0≤ x ≤0.1) and CuMo 1- y W y O 4 (0≤ y ≤0.1) over a wide range of temperatures.