Field-induced quantum magnetism in the verdazyl-based charge-transfer salt $[$$o$-MePy-V-($p$-Br)$_2]$FeCl$_4$

Y. Iwasaki; T. Kida; M. Hagiwara; T. Kawakami; Y. Kono; S. Kittaka; T. Sakakibara; Y. Hosokoshi; H. Yamaguchi

doi:10.1103/PhysRevB.98.224411

paper

Field-induced quantum magnetism in the verdazyl-based charge-transfer salt $[$ $o$ -MePy-V-( $p$ -Br) $_{2}]$ FeCl $_{4}$

arXiv:1812.08334 · doi:10.1103/PhysRevB.98.224411

Abstract

We successfully synthesized a verdazyl-based charge-transfer salt $[$ $o$ -MePy-V-( $p$ -Br) $_{2}]$ FeCl $_{4}$ , which has an $S_{V}$ =1/2 on the radical $o$ -MePy-V-( $p$ -Br) $_{2}$ and an $S_{Fe}$ =5/2 on the FeCl $_{4}$ anion. $A b$ $ini t i o$ molecular orbital calculations indicate the formation of an $S_{V}$ =1/2 honeycomb lattice composed of three types of exchange interaction with two types of inequivalent site. Further, the $S_{V}$ =1/2 at one site is sandwiched by $S_{Fe}$ =5/2 spins through antiferromagnetic (AF) interactions. The magnetic properties indicate that the dominant AF interactions between the $S_{V}$ = 1/2 spins form a gapped singlet state, and the remaining $S_{Fe}$ = 5/2 spins cause an AF order. The magnetization curve exhibits a linear increase up to approximately 7 T, and an unconventional 5/6 magnetization plateau appears between 7 T and 40 T. We discuss the differences between the effective interactions associated with the magnetic properties of the present compound and ( $o$ -MePy-V)FeCl $_{4}$ . We explain the low-field linear magnetization curve through a mean-field approximation of an $S_{Fe}$ = 5/2 spin model. At higher field regions, the 5/6 magnetization plateau and subsequent nonlinear increase are reproduced by the $S_{V}$ = 1/2 AF dimer, in which a particular internal field is applied to one of the spin sites. The ESR resonance signals in the low-temperature and low-field regime are explained by conventional two-sublattice AF resonance modes with easy-axis anisotropy. These results demonstrate that exchange interactions between $S_{V}$ = 1/2 and $S_{Fe}$ = 5/2 spins in $[$ $o$ -MePy-V-( $p$ -Br) $_{2}]$ FeCl $_{4}$ realize unconventional magnetic properties with low-field classical behavior and field-induced quantum behavior.

arXiv commentarXiv admin note: text overlap with arXiv:1706.07546

Field-induced quantum magnetism in the verdazyl-based charge-transfer salt $[$ $o$ -MePy-V-( $p$ -Br) $_{2}]$ FeCl $_{4}$

Abstract

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Field-induced quantum magnetism in the verdazyl-based charge-transfer salt [o-MePy-V-(p-Br)2​]FeCl4​

Abstract

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Field-induced quantum magnetism in the verdazyl-based charge-transfer salt $[$ $o$ -MePy-V-( $p$ -Br) $_{2}]$ FeCl $_{4}$