Pressure Effect on Bulk Weak Ferromagnets: (BDH-TTP)[M(isoq)2(NCS)4] (M = CrIII, FeIII; isoq = Isoquinoline)

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• 作者：Satoshi Kudo ; Akira Miyazaki ; Toshiaki Enoki ; Sté ; phane Golhen ; Lahcè ; ne Ouahab ; Takashi Toita ; and Jun-ichi Yamada
• 刊名：Inorganic Chemistry
• 出版年：2006
• 出版时间：May 1, 2006
• 年：2006
• 卷：45
• 期：9
• 页码：3718 - 3725
• 全文大小：239K
• 年卷期：v.45,no.9(May 1, 2006)
• ISSN：1520-510X

文摘

The pressure dependence of the magnetic properties of weak ferromagnets (BDH-TTP)[M(isoq)₂(NCS)₄] [BDH-TTP = 2,5-bis(1',3'-dithiolan-2'-ylidene)-1,3,4,6-tetrathiapentalene; M = Cr, Fe; isoq = isoquinoline] is discussed.These salts form two-dimensional magnetic sheets, where ferrimagnetic chains of donor cation radical (S = ¹/₂)and anion [S = ³/₂ (Cr), ⁵/₂ (Fe)] are antiferromagnetically connected by weak donor-donor and anion-anioninterchain S···S contacts. Under ambient pressure, both the Cr and Fe salts undergo a weak ferromagnetic transitionat T_c = 7.6 K, below which a spontaneous magnetization emerges along the direction perpendicular to the sheets.The application of the pressure elevates the transition temperatures up to 16.6 and 11.6 K at 9 kbar for M = Crand Fe, respectively. As the pressure increases, the remanent magnetization M_r decreases, whose pressuredependence for the Cr salt is larger than that for the Fe salt. This difference indicates that the spin-canting angleof the Cr salt is reduced because of the increase of antiferromagnetic interaction by applied pressure, in contrastto the Fe salt, where single-ion anisotropy contributes less. The quantitative analysis of the magnetization curvesof the Cr salt using the mean-field approximation reveals that the intermolecular exchange interaction increases asthe pressure increases, among which the interchain anion-anion interaction has the highest pressure sensitivity.This result is consistent with the temperature dependence of the crystal structure showing that the thermal contractionin the distances of interchain anion-anion S···S contacts is the most remarkable in intrachain S···S contacts. Thelarge pressure dependence of the transition temperature of these salts is therefore explained as a result of the factthat the interchain interactions, the anion-anion interaction in particular, are strengthened by applied pressure.