Magnetic correlations of the quasi-one-dimensional half-integer spin-chain antiferromagnets SrM2V2O8(M = Co, Mn)

Magnetic correlations of two iso-structural quasi-one-dimensional (1D)\nantiferromagnetic spin-chain compounds Sr$M_2$V$_2$O$_8$ ($M$ = Co, Mn) have\nbeen investigated by magnetization and powder neutron diffraction. Two\ndifferent collinear antiferromagnetic (AFM) structures, characterized by the\npropagation vectors, $k$ = (0 0 1) and $k$ = (0 0 0), have been found below\n$\\sim$ 5.2 K and $\\sim$ 42.2 K for the Co- and Mn-compounds, respectively. For\nthe Mn-compound, AFM chains (along the $c$ axis) order ferromagnetically within\nthe $ab$ plane, whereas, for the Co-compound, AFM chains order\nferro-/antiferromagnetically along the $a/b$ direction. The critical exponent\nstudy confirms that the Co- and Mn-compounds belong to the Ising and Heisenberg\nuniversality classes, respectively. For both compounds, short-range spin-spin\ncorrelations are present over a wide temperature range above $T_N$. The reduced\nordered moments at base temperature (1.5 K) indicate the presence of quantum\nfluctuations in both compounds due to the quasi-1D magnetic interactions.\n