Coercive Fields Above 6 T in Two Cobalt(II)–Radical Chain Compounds

Abstract

Lanthanide permanent magnets are widely used in applications ranging from nanotechnology to industrial engineering. However, limited access to the rare earths and rising costs associated with their extraction are spurring interest in the development of lanthanide‐free hard magnets. Zero‐ and one‐dimensional magnetic materials are intriguing alternatives due to their low densities, structural and chemical versatility, and the typically mild, bottom‐up nature of their synthesis. Here, we present two one‐dimensional cobalt(II) systems Co(hfac)2(R‐NapNIT) (R‐NapNIT=2‐(2′‐(R‐)naphthyl)‐4,4,5,5‐tetramethylimidazoline‐1‐oxyl‐3‐oxide, R=MeO or EtO) supported by air‐stable nitronyl nitroxide radicals. These compounds are single‐chain magnets and exhibit wide, square magnetic hysteresis below 14 K, with giant coercive fields up to 65 or 102 kOe measured using static or pulsed high magnetic fields, respectively. Magnetic, spectroscopic, and computational studies suggest that the record coercivities derive not from three‐dimensional ordering but from the interaction of adjacent chains that compose alternating magnetic sublattices generated by crystallographic symmetry.

Magnetic Anisotropy Drives Magnetochiral Dichroism in a Chiral Molecular Helix Probed with Visible Light

“…34,36 The need to overcome the stronger intrachain exchange interaction appears at the origin of extremely high coercivity observed in some chain-based materials. 27,[37][38][39] It is interesting to compare the low temperature dynamics with that expected for this Mn III chain in the absence of interchain interactions. Taking into account the model developed for canted antiferromagnetic chains, 27 the activation energy is given by…”

Two-Dimensional Nitronyl Nitroxide–Cu Networks Based on Multi-Dentate Nitronyl Nitroxides: Structures and Magnetic Properties

“…The metal-radical heterospin strategy, in which metal ions link with stable organic radicals, is extremely fascinating for designing molecular magnetic materials [1][2][3][4][5][6]. Based on this kind of heterospin approach, 3d [7][8][9], 4f [10][11][12][13][14][15][16][17], and 3d-4f [18][19][20][21][22][23] compounds have been obtained so far by employing various organic radicals, such as N 2 3− [15,16], HAN 3− [24], TTF + [25], thiadiazoyl [14], and nitronyl nitroxide radical ligands [6,7,10,13,19,23,[26][27][28][29][30][31][32]. In particular, nitronyl nitroxide radicals are often used as building blocks to construct metal compounds with various topology structures due to the substituent groups of nitronyl nitroxides being able to effectively regulate the spatial arrangement of magnetic building blocks [33].…”

“…In particular, nitronyl nitroxide radicals are often used as building blocks to construct metal compounds with various topology structures due to the substituent groups of nitronyl nitroxides being able to effectively regulate the spatial arrangement of magnetic building blocks [33]. However, it is worth noting that most of the nitronyl nitroxide-metal compounds display zero- [34][35][36][37] and one-dimensional (1D) structures [10,11,26,27], while nitronyl nitroxide radicals bridged two-dimensional (2D) metal complexes are scarce so far. This could be attributed to the fact that metal centers require electron-attracting coligands, such as hexafluoroacetylacetonate, to promote the coordination of nitronyl nitroxide radicals.…”

A metal-radical hetero-tri-spin SCM with methyl–pyrazole–nitronyl nitroxide bridges

“…46,51 An interestingly feature for this material are the two contributions to the AC susceptibility observed in the same temperature range. SCM behavior concomitant to an antiferromagnetic 54,55 or ferromagnetic 53 ordering is often found but this is clearly not the case for 2. In present case, both contributions are characterized by a slow relaxation of the magnetization, one clearly associated to a SCM while second remains to be understood.…”

“…The behavior of C2 is similar to that usually observed for an SCM. 51,52 The origin of C1 is more puzzling and likely related to inter-chain interactions; 53 but ferromagnetic ordering can be ruled out because of the shift of the χ M ' and χ M '' signals with temperature, and of the decreasing χ M '' signal with frequency. Finally, when AC data were recorded with an applied DC field of 1 kOe, only the maximum for χ M '' versus ν in the higher frequency domain (i.e.…”