空気に触れると、新しいナノ材料は高温で磁性を帯びる（When exposed to air, new nanomaterial becomes magnetic at high temperatures）

2026-08-31 ワシントン大学（UW）

＜関連情報＞

• https://www.washington.edu/news/2026/08/31/august-research-highlights-nectar-robbing-anxious-attachment-styles-persnickety-plasma-more/
• https://pubs.acs.org/jacsat/article-abstract/148/33/35898/5255804/Synthesis-and-Magnetism-of-Silver-Chromium

銀クロムセレン化物スピネルの合成と磁性 Synthesis and Magnetism of Silver Chromium Selenide Spinels

Ezra K. Bacon-Gershman;Samantha M. Harvey;Charlize Agag;Abdul Moeez;Guodong Ren;Sonder Wilson;Yinuo Xu;Daniel R. Gamelin;Lilo Pozzo;Juan Carlos Idrobo;Brandi M. Cossairt
Journal of the American Chemical Society
DOI:https://doi.org/10.1021/jacs.6c09346

Abstract

Chalcogenide spinels exhibit electronic and magnetic properties that are tunable through lattice occupancy and composition. Here, we report the first synthesis of spinel-phase Ag₂Cr₂Se₄ and AgCr₂Se₄ and demonstrate an oxidation-induced ferro-to-ferrimagnetic transition accompanied by a massive increase in T_C of >250 K associated with changes in Ag⁺ site occupancy. The Ag spinels are synthesized through air-free cation exchange of CuCr₂Se₄ nanocrystals driven by excess AgNO₃ to yield ferromagnetic Ag₂Cr₂Se₄ (a = 10.838(4) Å, T_C = 152 K, 2 K saturation = 3.1 μ_B/Cr) with Ag⁺ occupying both T_d 8a and O_h 16c sites. Upon air exposure, Ag₂Cr₂Se₄ converts to ferrimagnetic AgCr₂Se₄ (a = 10.6085(19) Å, T_C > 400 K, 2 K saturation = 2.2 μ_B/Cr) through a loss of O_h-Ag⁺ alongside the formation of Ag₂Se. We attribute the ferro-to-ferrimagnetic transition to the generation of holes in Ag–Se bands, which couple antiferromagnetically to Cr³⁺. This Ag–Cr–Se spinel system demonstrates the largest change in T_C reported and provides an excellent framework for further exploration of magnetic coupling as a function of oxidation and structure.