THE MAGNETIC-STRUCTURES OF MN2PO4F AND CO2PO4F AT 1.2 K

The hydrothermal growth of two fluorophosphates Mn2PO4F and Co2PO4F is performed in 15 M H3PO4 (T = 973 K, P = 200 MPa). Mn2PO4F and Co2PO4F are antiferromagnetic (T-N = 15 K, theta(p) = -50 K and T-N = 14 K, t heta(p) = -53 K, respectively). The magnetic and nuclear structures ar e solved at 1.2 K. In Mn2PO4F, the magnetic moments of Mn(1) and Mn(2) (mu = 4.22(5) mu(B)) are aligned antiferromagnetically along the b-ax is of the monoclinic cell (space group C2/c, Z = 8, a = 13.395(6) Angs trom, b = 6.495(2) Angstrom, c = 10.078(5) Angstrom, and beta = 120.11 (3)degrees at T = 1.2 K). Infinite ferromagnetic chains of spins, orie nted along the [101] and [010] directions, correspond to infinite chai ns of Mn2+ nuclear cell of Co2PO4F (a = 9.680(5) Angstrom, b = 12.769( 2) Angstrom, c = 11.974(7) Angstrom, beta = 108.24(7)degrees, Z = 16) is described at 23 K in the P2(1)/c space group with Co2+ in eight gen eral 4e positions. The Co2+ ions adopt either a fivefold or an octahed ral coordination. At 1.2 K, the magnetic cell is enlarged along a (a(m ag) = 2a(nucl)) and two nuclear cells, adjacent along a, are antiferro magnetic. The magnetic structure is complex and noncollinear; ferromag netic dimers are found in [100] chains of edge-sharing CoO4F2 octahedr a, while four consecutive spins in a [100] chain of CoO4F polyhedra ad opt a spiral arrangement.