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The Crystal Structure and Magnetic Properties of a New Ferrimagnetic Semiconductor:  Ca21Mn4Sb18

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posted on 14.02.2003, 00:00 by Aaron P. Holm, Marilyn M. Olmstead, Susan M. Kauzlarich
Single crystals of the new transition metal Zintl phase, Ca21Mn4Sb18, were prepared by high temperature melt synthesis. The crystal structure was determined by single crystal X-ray diffraction to be monoclinic in the space group C2/c. Crystal information was obtained at 90 K, and unit cell parameters were determined (a = 17.100(2) Å, b = 17.073(2) Å, c = 16.857(2) Å, β = 92.999(2)°, Z = 2, R1 = 0.0540, wR2 = 0.1437). The structure can be described as containing 4 discreet units per formula unit:  1 linear [Mn4Sb10]22- anion, 2 dumbbell-shaped [Sb2]4- anions, 4 individual Sb3- anions, and 21 Ca2+ cations. The [Mn4Sb10]22- anion contains four edge-shared MnSb4 tetrahedra with distances between Mn ions of 3.388(4) Å, 2.782(4) Å, and 2.760(4) Å. Electron counting suggests that the Mn are 2+. Temperature dependent magnetization shows a ferromagnetic-like transition temperature at ∼52 K which is suppressed with increasing magnetic field. The paramagnetic regime is best fit to a ferrimagnetic model, providing a total effective moment of 4.04(2) μB, significantly less than that expected for 4 Mn2+ ions (11.8 μB). Temperature dependent resistivity shows that this compound is a semiconductor with an activation energy of 0.159(2) eV (100−300 K).

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