The Canted Antiferromagnetic Approach to Single-Chain Magnets

The reaction of manganese(III) acetate meso-tetraphenylporphyrin with phenylphosphinic acid
provides the one-dimensional compound of formula [Mn(TPP)O2PHPh]·H2O, which crystallizes in the
monoclinic C2/c space group. The chain structure is generated by a glide plane resulting in Jahn−Teller
elongation axes of the MnIII octahedra that alternate along the chain. The phenylphosphinate anion transmits
a sizable antiferromagnetic exchange interaction that, combined with the easy axis magnetic anisotropy of
the MnIII sites, gives rise to a canted antiferromagnetic arrangement of the spins. The static single-crystal
magnetic properties have been analyzed with a classical Monte Carlo approach, and the best fit parameters
for the exchange and single ion anisotropy are J = −0.68(4) K and D = −4.7(2) K, respectively (using the
−2JSiSj formalism for the exchange). Below 5 K the single-crystal dynamics susceptibility reveals a
frequency-dependent out-of-phase signal typical of single-chain magnets. The extracted relaxation time
follows the Arrhenius law with Δ = 36.8 K. The dynamic behavior has been rationalized and correlated to
geometrical parameters of the structure. The contribution of the correlation length to the energy barrier
has been investigated, and it has been found that the characteristic length that dominates the dynamics
strongly exceeds the correlation length estimated from magnetic susceptibility.