Stripe order and magnetic anisotropy in the S=1 antiferromagnet BaMoP2O8

Abstract

Magnetic behavior of yavapaiite-type BaMoP2O8 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 k = ( 1 2 , 1 2 , 1 2 ) formed below TN 21 K. This stripe phase is triggered by a pronounced onedimensionality of the spin lattice, where one of the in-plane couplings, J2 4.6 meV, is much stronger than its J1 0.4 meV counterpart, and stabilized by the weak easy-axis anisotropy. The ordered moment of 1.42(9) µB at 1.5 K is significantly lower than the spin-only moment of 2 µB due to a combined effect of quantum fluctuations and spin-orbit coupling.

Large easy-axis anisotropy in the one-dimensional magnet BaMo(PO4)2

“…Upon cooling, a broad maximum characteristic of short-range correlations is seen at T max = 55 K, followed by an inflection point at T N = 22 K, associated with magnetic long range order. While the latter feature is consistent with the previous study 22 , we also find a previously unobserved anomaly in our specific heat data at this temperature [ Fig. 3…”

“…3(a). Within the temperature interval 200 to 300 K, χ m (T ) obeys the Curie-Weiss law χ m (T ) = C/(T − θ) + χ 0 , with a Curie constant C = 0.88(2) emu K mol −1 and a large antiferromagnetic Weiss constant θ CW = −167.0(5) K. Both values are consistently considerably higher than those reported in Hembacher et al 22 regardless of the temperature fitting range used. This could be relevant to the difference in sample quality and preparation method.…”

“…The preparation of the polycrystalline BaMo(PO 4 ) 2 samples used in this study follows a distinct procedure from the previously reported synthetic routes 22,24 . Stoichiometric amounts of BaCO 3 (Alfa Aesar 99.9%), MoO 2 (Alfa Aesar 99.0%), and (NH 4 ) 2 HPO 4 (Alfa Aesar 98+%) were intimately mixed and heated for 12 hours in a tube furnace at 873 K under vacuum.…”

“…The inset shows the magnetic contribution to the specific heat as obtained by subtracting the phonon contribution using a polynomial form Cp = a1T 3 + a2T 5 + a3T 7 fitted to the high-temperature data. An anomaly, previously not observed in the previous work 22 , is seen at TN = 22 K. anisotropy should be small, we choose the S = 1 Heisenberg anisotropic triangular lattice model as a starting point to fit the magnetic susceptibility. The HTE10 code 31 was used to calculate the [4,6] Padé approximant of the 10 th order high-temperature series expansion of this model.…”

“…The inclusion of a magnetic 4d cation means that anisotropic terms, both single-ion and exchange, should be much more prominent than in the 3d systems mentioned above. Indeed, a previous experimental and theoretical study of BaMo(PO 4 ) 2 indicates that the system orders at a relatively high temperature T N = 21 K relative to the dominant exchange of J ∼ 40 K, i.e θ CW /T N ∼ 2 22,23 . Since the interchain coupling is estimated to be small ∼ 0.1J, well below the threshold to close the Haldane gap, and because the magnetic structure is collinear, strong easyaxis anisotropy is anticipated.…”