Magnetic Phase Diagram of CuO

Abstract

High resolution ultrasonic velocity measurements have been used to determine the temperature -- magnetic-field phase diagram of the monoclinic multiferroic CuO. A new transition at TN3 = 230 K, corresponding to an intermediate state between the antiferromagnetic non-collinear spiral phase observed below TN2 = 229.3 K and the paramagnetic phase, is revealed. Anomalies associated with a first order transition to the commensurate collinear phase are also observed at TN1 = 213 K. For fields with B along the b axis, a spin-flop transition is detected between 11 T - 13 T at lower temperatures. Moreover, our analysis using a Landau-type free energy clearly reveals the necessity for an incommensurate collinear phase between the spiral and the paramagnetic phase. This model is also relevant to the phase diagrams of other monoclinic multiferroic systems.

5 pages, 5 figures

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• Magnetically driven ferroelectric order in Ni${}_3$V${}_2$O${}_8$
• Multiferroic properties and magnetic structure of Sm1-xYxMnO3
• Directional magnetoelectric effects in MnWO4: magnetic sources of the electric polarization
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• Magnetic Excitations of the Hybrid Multiferroic (ND4)2FeCl5D2O
• Interpretation of magnetoelectric phase states using the praphase concept and exchange symmetry
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