Ferromagnetic Ising chains in frustrated LnODCO₃: the influence of magnetic structure in magnetocaloric frameworks

Abstract

Understanding how to tune magnetic interactions to optimise the magnetocaloric effect is crucial for designing more efficient solid state refrigerants; this work probes this relationship for the promising LnODCO3 phases.

In situ observation of the magnetocaloric effect through neutron diffraction in the Tb(DCO2)3 and TbODCO3 frameworks

“…8,33 We have previously established the magnetic states that form in both Tb(HCO 2 ) 3 and TbOHCO 3 in the absence of applied magnetic fields. 9,35 Tb(HCO 2 ) 3 , which adopts R3m rhombohedral symmetry at all measured temperatures, 36 shows strong diffuse scattering indicative of short range order below 20 K, where its magnetocaloric effect begins to be significant. This short range order is formed of ferromagnetically coupled linear chains of Isinglike moments aligned along the c-axis, antiferromagnetically coupled in a triangular array within the ab plane.…”

“…It has previously been shown that Tb(HCO 2 ) 3 and TbOHCO 3 undergo transitions to the TIA phase at B1.6 K and an antiferromagnetic state at B1.2 K, respectively. 9,36,43 Above their ordering temperatures these materials both contain short range ferromagnetic Ising chains in the correlated paramagnetic phase, asserted to be responsible for their highly efficient magnetocaloric effects. 8,9 Variable field measurements above and below these transitions show features suggestive of the ordering behaviour.…”

“…Advanced functional magnetic materials with finely tuned properties are relevant to a broad range of modern technologies, finding applications from data storage/transfer [1][2][3] to medicine. 4 Optimising such materials, including multiferroics [5][6][7] and magnetocalorics, [8][9][10][11] requires a detailed understanding of how they respond to an applied magnetic field. There is also great fundamental interest in magnetic phenomena that emerge with increasing applied magnetic fields, including metamagnetic spin-flop and spin-flip transitions, [12][13][14][15][16] exotic magnetic states in Ising 1D chains and magnetisation plateaus.…”

“…TbODCO 3 , which adopts P2 1 2 1 2 1 orthorhombic symmetry, also shows strong diffuse scattering below 20 K attributed to the formation of ferromagnetic correlations between the Ising-like cations in the buckled ferromagnetic chains along the b-axis, which are packed into an antiferromagnetic triangular like lattice. 9 These buckled chains present an additional source of entropy in these systems, potentially responsible for the higher magnetocaloric effect observed. 33 Below 1.2 K physical property measurements indicate the emergence of an ordered state and, in the isostructural HoODCO 3 , corresponds to a quasi-long range ordered antiferromagnet.…”

“…33 Below 1.2 K physical property measurements indicate the emergence of an ordered state and, in the isostructural HoODCO 3 , corresponds to a quasi-long range ordered antiferromagnet. 9 It has been proposed that the suppression of the frustrated antiferromagnetic interactions in Tb(HCO 2 ) 3 and TbOHCO 3 enable high entropy changes in small applied magnetic fields. 8,33 This is consistent with the rapid increases in their magnetisation under modest fields, 8,33 contributing to a high efficiency as a magnetocaloric.…”