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MA: Magnetismus

MA 27: Spinstrukturen und magnetische Phasenüberg
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MA 27.7: Vortrag

Donnerstag, 27. März 2003, 16:45–17:00, HSZ/405

Unusual magnetic-field dependence of partially frustrated triangular ordering in manganese tricyanomethanide — •Ralf Feyerherm¹, Anja Loose¹, and Jamie L. Manson² — ¹Hahn-Meitner-Institut, 14109 Berlin — ²Oak Ridge National Laboratory, U.S.A.

Heat capacity and neutron diffraction experiments reveal that manganese tricyanomethanide, Mn[C(CN)₃]₂, exhibits partially frustrated magnetic ordering below 1.18 K. The zero-field magnetic structure consists of an incommensurate spiral with propagation vector Q = (0.622 0 0). We show that the system can be mapped onto the No-dqrow modelNo-dq for partially frustrated triangular magnets, with a larger magnetic interaction J along rows of Mn²⁺ ions (S = 5/2) than between the rows (J′), with J′/J = 0.749. The magnetic-field dependence of the intensity of the magnetic Bragg reflections for H//Q indicates the presence of three different magnetic phases that we associate with the incommensurate spiral, the up-up-down phase, and the No-dq2-1No-dq spin-flop like magnetic structure proposed for related compounds. For increasing fields, Q varies continuously, reaching the value 2/3, corresponding to the commensurate spiral of the fully frustrated triangular lattice, at 19 kOe. At this point, the field-dependence reverses, so that except for this specific field value the magnetic ordering is incommensurate in all three field dependent magnetic phases of Mn[C(CN)₃]₂.