Magnetostrictive Néel ordering of the spin-52ladder compound BaMn2O

Abstract

The crystal structure and the magnetism of BaMn2O3 have been studied by thermodynamic and by diffraction techniques using large single crystals and powders. BaMn2O3 is a realization of a S = 5/2 spin ladder as the magnetic interaction is dominant along 180• Mn-O-Mn bonds forming the legs and the rungs of a ladder. The temperature dependence of the magnetic susceptibility exhibits well-defined maxima for all directions proving the low-dimensional magnetic character in BaMn2O3. The susceptibility and powder neutron diffraction data, however, show that BaMn2O3 exhibits a transition to antiferromagnetic order at 184 K, in spite of a full frustration of the nearestneighbor inter-ladder coupling in the orthorhombic high-temperature phase. This frustration is lifted by a remarkably strong monoclinic distortion which accompanies the magnetic transition.

S = 2 Spin Ladders in the Sulfide Oxide BaFe2S2O

“…On the basis of local density approximation (LDA) calculations, Han et al suggested ferromagnetic spin interactions along the ladders, [6] but this has to be confirmed by neutron diffraction. However, a symmetry breaking was the reason for long-range magnetic ordering in BaMn 2 O 3 [4] and a small staggering between the ladders in α-BaFe 2 Se 3 is observed on magnetic ordering (i.e., there is a strong magnetoelastic coupling even without intrinsic geometric frustration). [14] Moreover, extra phonons appear in the Raman data below 240 K in BaFe 2 Se 2 O.…”

“…However, the low-temperature spin ordering could be different in the two modifications. In other ladder compounds (e.g., BaMn 2 O 3 ), [4] the low-dimensional magnetic behavior is clearly due to the geometric frustration between the ladders, marked for the title compound with dashed lines in Figure 2b. Hence, the crystallographic mirror plane with its normal parallel to the a axis might play an important role in the magnetic properties of both BaFe 2 S 2 O and BaFe 2 Se 2 O, as both dashed lines have to result in two equally strong antiferromagnetic couplings between the ladders.…”

“…[3] Also, classic Heisenberg spins S = 5/2 have been found on ladders in BaMn 2 O 3 , and the magnetic ordering is accompanied by a strong structural distortion. [4] The S = 2 ladders are still rare, but recent investigations of compounds related to a β-BaFe 2 S 3 -type structure [5] revealed new compounds with characteristic magnetic properties: Two independent research groups discovered BaFe 2 Se 2 O, [6,7] in which Se and O enter the two different crystallographic S sites in the β-BaFe 2 S 3 -type structure without intermixing. These first reports pointed at low-dimensional magnetic behavior, and spectroscopic investigations confirmed the existence of short-range spin correlations even above the Néel transition at 240 K. [8] Here, we present the synthesis and characterization of BaFe 2 S 2 O, a further extension to the S = 2 ladder compounds.…”

Strong magnetoelastic coupling at the transition from harmonic to anharmonic order inNaFe(WO4)2with3d5Simon1, Ackermann2, Chapon3 et al. 2016Phys. Rev. BSelf Cite134220View full textAdd to dashboardCite

“…In contrast, the onset of incommensurate harmonic order at T N has no magnetoelastic impact on the b lattice parameter. In most magnetoelastic materials [26][27][28][29][30] , anomalies in the strain are coupled to the order parameter, typically the (staggered) magnetic moment, and thus appear just at T N , while the situation in NaFe(WO 4 ) 2 is more complex. In NaFe(WO 4 ) 2 , the change in the lattice is not proportional to a power of the averaged ordered moment, |m| , but to the emergence of anharmonicity either in the incommensurate phase or in the commensurate order.…”

“…Firstly, the effects are rather large yielding a relative reduction of the b lattice param- eter by up to ∆b b −2.6 · 10 −4 , and, secondly, there is no magnetoelastic anomaly at the onset of magnetic ordering in zero field, which results in the incommensurate phase. In most systems with strong magnetoelastic effects one may couple the strain, , with some power of the ordered moment defined as m av = |m| [26][27][28][29][30]40 , but in NaFe(WO 4 ) 2 the intermediate incommensurate phase renders the analysis more complex. Apparently there is only a weak coupling to the incommensurate phase, while that to the commensurate order parameter is strong.…”