Stripe order and magnetic anisotropy in the $S=1$ antiferromagnet BaMoP${}_2$O${}_8$

Abstract

Magnetic behavior of BaMoP${}_2$O${}_8$ with the spatially anisotropic triangular arrangement of the $S=1$ Mo${}^{4+}$ ions is explored using thermodynamic measurements, neutron diffraction, and density-functional band-structure calculations. A broad maximum in the magnetic susceptibility around 46\,K is followed by the stripe antiferromagnetic order with the propagation vector $\mathbf{k}=(\frac{1}{2},\frac{1}{2},\frac{1}{2})$ formed below $T_N\simeq 21$ K. This stripe phase is triggered by a pronounced one-dimensionality of the spin lattice, where one of the in-plane couplings, $J_2\simeq 4.6$ meV, is much stronger than its $J_1\simeq 0.4$ meV counterpart, and stabilized by the weak easy-axis anisotropy. The ordered moment of 1.42(9) ${\mu }_B$ at 1.5 K is significantly lower than the spin-only moment of 2 ${\mu }_B$ due to a combined effect of quantum fluctuations and spin-orbit coupling.

10 pages, 7 figures