鮮やかな色変化をする相転移のメカニズムを超高速分光で解明！～長年謎だった光誘起電荷移動型スピン転移現象の しくみが明らかに～

2025-06-06 東京大学

＜関連情報＞

• https://www.s.u-tokyo.ac.jp/ja/press/10789/#
• https://www.nature.com/articles/s41467-025-60401-4

コバルト-タングステン酸分子光磁性体における超高速電荷移動誘起スピン転移 Ultrafast charge-transfer-induced spin transition in cobalt-tungstate molecular photomagnets

Kazuki Nakamura,Laurent Guérin,Gaël Privault,Koji Nakabayashi,Marius Hervé,Eric Collet & Shin-ichi Ohkoshi
Nature Communications  Published:06 June 2025
DOI:https://doi.org/10.1038/s41467-025-60401-4

Abstract

In materials exhibiting photoinduced phase transitions, and in which both charge transfer and spin transitions occur, there has long been a debate about which process drives the phase transition. Herein, we present experimental evidence supporting an optically charge-transfer-induced spin transition (CTIST) process, as demonstrated through femtosecond optical spectroscopy in two-dimensional cyanido-bridged cobalt-tungstate photomagnets. Optical and magnetic studies revealed that the photoexcitation of the ground low-temperature (LT) Co^III_LS-W^IV state leads to a photoinduced phase transition towards the Co^II_HS-W^V state, which is similar to the high temperature (HT) state. Ultrafast spectroscopy further indicates that this optical excitation of the intermetallic W-to-Co charge-transfer band produces a transient photoexcited (PE) Co^II_LS-W^V state, which decays within 130 fs through a spin transition towards the Co^II_HS-W^V state. Here we show that the CTIST dynamics corresponds to the Co^III_LS-W^IV (LT) → Co^II_LS-W^V (PE) → Co^II_HS-W^V (HT) sequence. The present work sheds a new light on understanding optical dynamics underlying the photoinduced phase transitions.