Metamagnetic Transitions versus Magnetocrystalline Anisotropy in Two Cobalt Arsenates with 1D Co²⁺ Chains

Abstract

We have investigated two original hydrated cobalt arsenates based on Co 2+ octahedral edgesharing chains. Their different magnetocrystalline anisotropies induce different types of metamagnetic transition, spin-flop versus spin-flip. In both compounds, a strong local anisotropy (Ising spins) is favored by the spin-orbit coupling present in the CoO6 octahedra while ferromagnetic (FM) exchanges predominate in the chains. Co2(As2O7), 2H2O (1) orders antiferromagnetically below TN = 6.7 K. The magnetic structure is a non-collinear antiferromagnetic spin arrangement along the zigzag chains with DFT calculations imply frustrated chains and weakened anisotropy. A metamagnetic transition suggests a spin-flop process above 0H = 3.2 T. On the contrary, BaCo2As2O8.2H2O (2) linear chains are arranged in disconnected layers, with only inter-chain ferromagnetic exchanges and therefore increasing its magnetocrystalline anisotropy. The magnetic structure is collinear with a magnetic easy axis that allows a spin-flop to a sharp spin-flip transition below TN= 15.1 K and above 0H = 6.2 T.

CoMOF5(pyrazine)(H2O)2 (M = Nb, Ta): Two-Layered Cobalt Oxyfluoride Antiferromagnets with Spin Flop Transitions

“…Such a Co–Co network in the ab -plane leads to the formation of a triangular fashion, which may lead to frustration for strong quantum fluctuation. This frustration could be one possible reason for weakening magnetic anisotropy in 1 and 2 . Also, such frustrated triangular lattice in the ab -plane, together with low dimensionality prohibit the appearance of long-range antiferromagnetic order until 3.7 K for 1 and 2 .…”

“…Relatively weak magnetic anisotropy could lead to the spin flop transition, , as observed in 1 and 2 with g = 3.1 for 1 (3.42 for 2 ). Spin flop transitions are not observed in all reported Co 2+ compounds but only a few of them, to the best of our knowledge, including [H 2 en]­Co­(HSeO 3 ) 2 Cl 2 (en = ethylenediamine), A′Co 3 PO 4 O 14 (A′ = Ba, Sr), Co­(PDA)­(4,4′-bpy) · H 2 O (H 2 PDA = 1,4-phenylenediacetic acid; 4,4′-bpy = 4,4′-bipyridyl), Co­(N 3 )­(tzbp) (Htzbp = 6-(1 H -tetrazol-5-yl)-2,2′-bipyridine), Co 2 As 2 O 7 · 2H 2 O, and Co 4 Nb 2 O 9…”

Fragile magnetic ordering between robust 2D-ferrimagnets in the AFe3(SeO3)2F6 (A = K, Rb, Cs) series

“…10 Oe, followed by a subsequent drop. Even at such low field the maxima depend on the sample magnetic history and hysteretic wT(T) peaks are observed in ZFC/FC 13 Hence, our data suggest the loss of uniaxial spins together with a relatively weak magnetocrystalline under applied field. It is noteworthy that the experimental T N values are very similar (B120 K) for all compounds, a counter-intuitive behavior if one considers the expected variation of the Fe-Fe spin-exchanges (SEs) across the [Alkali] interleaves with a versatile size, see Fig.…”

Multiferroic BaCoX2O7 (X = P, As) Compounds with Incommensurate Structural Waves but Collinear Spin Ingredients

“…The situation of BaFeP 2 O 7 versus BaCoX 2 O 7 is reminiscent of the recent report of the spin flop occurring in BaCo 2 As 2 O 8 ⋅2H 2 O within a zigzag spin structure versus the spin‐flip transition in Co 2 As 2 O 7 ⋅2H 2 O with a collinear spin ordering. [ 13 ] On this basis, the “flip”‐ versus “flop”‐like transition types for Co 2+ and Fe 2+ respectively suggest uniaxial‐collinear spin ordering in BaCoX 2 O 7 (experimentally verified in ref. [21]) against Heisenberg spins with a plausible noncolinear spin‐structure in BaFeP 2 O 7 .…”

“…[ 9,10 ] In addition, the effects of magnetic fields on low‐D structures open the route to other fascinating phenomena, such as Bose–Einstein condensation or novel field‐induced magnetic states such as skyrmions. [ 11 ] Here highly anisotropic Co 2+ spin chains may generate field‐induced particularities, such as incommensurate spin density waves (SDWs) in the screw AFM chain of BaCo 2 V 2 O 8 , [ 12 ] metamagnetic spin flip versus spin flop in Co 2+ chain systems, [ 13 ] spin dynamics and low‐field spin alignments in canted‐1D inorganic systems, i.e., BaCo 2 (As 3 O 6 ) 2 ⋅(H 2 O) 2 [ 14 ] analog to hybrid single‐chain magnets (SCMs). [ 15,16 ] Although ignored up to day, the access to noncollinear magnetic structures and magnetization steps suggest attractive ME properties.…”