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Crystal Distortions Associated with Magnetic Ordering in the Antiferromagnetic Compound VF 2

1970; International Centre for Diffraction Data; Volume: 14; Linguagem: Inglês

10.1154/s0376030800008533

2631-3626

W. S. McCain, Darryl Albright, W. O. J. Boo,

Inorganic Chemistry and Materials

Abstract Lattice constants were measured as a function of temperature by single crystal diffracrometry in the temperature range which includes the Néel temperature of VF 2 (T N = 7°K). The lattice constants of VF 2 (D 4h 14 =P4 2 m n m) were measured from room temperature down to 4.2°K. In this range rhe tetragonal c-axis contracts 0.58% from 3.2359 Å (RT) to 3.2170 Å (4.2°K). On the other hand, the a-axes show a net expansion of 0.18% from 4.8023 Å (RT) to 4.8110 Å at 4.2°K. The temperature dependence of the lattice constants can be correlated with anisotropy of exchange forces. Vanadium Ions occupy the center and corner positions of the unit cell. Strong magnetic interactions are directed parallel to the c-axis >001< with considerably weaker interactions parallel to the body diagonals >111< The relative strengths of the two exchange integrals are J >001< = 50 J >111<. As a consequence the magnetic ordering is one-dîmensional along the c-axis and the associated distortions arise from the strong magnetic interactions along this axis.