Magnetic relaxation versus 3D long-range ordering in {Dy₂Ba(α-fur)₈}_nfuroate polymers

Abstract

A novel Dy-complex formulated as {[Dy2Ba(α-C4H3OCOO)8·(H2O)4]·2H2O}n, {Dy2Ba(α-fur)8}n, has been synthesized, structurally characterized, and magnetically and thermally investigated as a function of field and temperature, down to 85 mK. The α-furoate ligands consolidate 1D zig-zag chains formed by Dy2 dimers separated by Ba ions. Ab initio calculations were used to determine the easy anisotropy axis direction, the gyromagnetic tensor components and the energy levels of each Dy. The heat capacity and susceptibility measurements allowed us to conclude that intradimer and interdimer interactions are ferromagnetic and of the same order, J'/k(B) ≈ J''/k(B) = +0.55 K. In the absence of an applied magnetic field, the dynamic relaxation of the magnetization occurs through the fast (τ(T) ~ 10(-5) s) spin-reversal of each of the individual Dys through a quantum tunneling (QT) process. A long-range 3D ordered state is achieved at T(N) = 0.25 K, in which the ferromagnetically coupled zig-zag chains (J'/k(B) ≈ J''/k(B) = +0.528(1) K) running along the c-axis are antiferromagnetically coupled to the adjacent chains (J'''/k(B) = -0.021(1) K). Critical slowing down of the QT time constant is observed when the temperature approaches T(N). Under the application of a magnetic field, the QT relaxation is replaced by an Orbach process (with energy barrier U/k(B) = 68 K and τ0 ~ 10(-9) s at H = 2 kOe) and a very slow (τ(s) ∼ 0.2 s) relaxation process. We propose and demonstrate the proof of concept of a spintronic device, in which two different relaxation rates can be selected, and on/off switched by magnetic field biasing. The dynamical behavior of this compound is compared with another furoate to discuss the effect of competitive interactions.

Heteronuclear {TbxEu1−x} furoate 1D polymers presenting luminescent properties and SMM behavior

“…37,68 Very slow processes affected by BE have been earlier observed in our α-fur compounds. 46,47,49 In the present mixed {Tb/Eu} complexes, the influence of BE effect is also clear, as demonstrated by the relaxation experiments that we performed at different SQUID pressure conditions (Fig. 13), where it is appreciated that the main relaxation peak is shifted to (an order of magnitude) larger frequencies by decreasing the chamber pressure.…”

“…The synthesis of (1) by method A was previously reported. 49 The same result was obtained by method B when we used as precursor EDX analysis: Energy-dispersive X-ray spectroscopy (EDX) analysis was used to investigate the composition of the samples. Fig.…”

Magnetic Slow Relaxation in a Metal–Organic Framework Made of Chains of Ferromagnetically Coupled Single‐Molecule Magnets

“…In a first approximation, the strong ferromagnetic coupling observed in Dy is expected to be a consequence of the μ 2 bridging mode of the oxygen atoms (O3 and O5), which bind the Dy III ion …”

“…These coherent domains create a “correlation length” ξ , which is observed when the magnetic interaction along the chain is strong enough when compared with the temperature and possible weak interchain interactions . The growth of ξ induces an exponential variation of χ M T according to Equation :‐ …”

High relaxation barrier in neodymium furoate-based field-induced SMMs

“…On the other hand, the τ LF (1/T ) and τ LF (H) dependencies of the very slow process observed for complex (1) are characteristic of a direct process affected by phonon-bottleneck (PB) effect, a mechanism that we have commonly encountered in polymeric furoate complexes. [27][28][29][30]43 The PB effect was indeed Table 3 Fit parameters for data shown in Fig. 7 using eqn demonstrated through relaxation measurements performed under different pressure conditions of the bath on complex (1) (S3): the χ″( f ) peak shifted to higher frequencies by increasing the pressure, and moved back reversibly by lowering the pressure (Fig.…”