Magnetic order, hysteresis, and phase coexistence in magnetoelectric LiCoPO4

Ellen Fogh, Rasmus Toft-Petersen, Eric Ressouche, Christof Niedermayer, Sonja Lindahl Holm, Maciej Bartkowiak, Oleksandr Prokhnenko, Steffen Sloth, Frederik Werner Isaksen, David Vaknin, Niels Bech Christensen

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The magnetic phase diagram of magnetoelectric LiCoPO4 is established using neutron diffraction and magnetometry in fields up to 25.9 T applied along the crystallographic b axis. For fields greater than 11.9 T, the magnetic unit cell triples in size with propagation vector Q = (0, 1/3,0). A magnetized elliptic cycloid is formed with spins in the (b, c) plane and the major axis oriented along b. Such a structure allows for the magnetoelectric effect with an electric polarization along c induced by magnetic fields applied along b. Intriguingly, additional ordering vectors Q ≈ to (0, 1/4,0) and Q ≈ to (0, 1/2,0) appear for increasing fields in the hysteresis region below the transition field. Traces of this behavior are also observed in the magnetization. A simple model based on a mean-field approach is proposed to explain these additional ordering vectors. In the field interval 20.5-21.0 T, the propagation vector Q = (0, 1/3,0) remains but the spins orient differently compared to the cycloid phase. Above 21.0 T and up until saturation, a commensurate magnetic structure exists with a ferromagnetic component along b and an antiferromagnetic component along c.
Original languageEnglish
Article number104420
JournalPhysical Review B
Issue number10
Number of pages10
Publication statusPublished - 2017

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©2017 American Physical Society

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Fogh, E., Toft-Petersen, R., Ressouche, E., Niedermayer, C., Holm, S. L., Bartkowiak, M., Prokhnenko, O., Sloth, S., Isaksen, F. W., Vaknin, D., & Christensen, N. B. (2017). Magnetic order, hysteresis, and phase coexistence in magnetoelectric LiCoPO4. Physical Review B, 96(10), [104420].