Magnetism of ACFs and superfluidity of 4He adsorbed in ACFs

College of Design and Manufacturing Technology, Muroran Institute of Technology, 27-1, Muroran, 050-8585, Japan

Adv. Mater. Lett., 2018, 9 (11), pp 760-766

DOI: 10.5185/amlett.2018.2129

Publication Date (Web): Jul 24, 2018

Copyright © IAAM-VBRI Press

E-mail: yshibaya@mmm.muroran-it.ac.jp

Abstract

Activated carbon fibers (ACFs) are a nanoporous form of carbon with huge specific surface areas caused by a three-dimensional random network of nanographites. Because of nano-size effects, non-bonding π-electron spins emerge on the nanographite. The nanographite random network produces many nanopores with a mean size of several nanometers and creates a host system for various guest molecules in ACFs. In order to investigate the magnetic properties of nanographite and the superfluidity of ⁴He restricted in nano-spaces, the magnetization of ACFs and superfluidity of ⁴He adsorbed in ACFs have been investigated. The magnetization shows an antiferromagnetic interaction between the non-bonding π-electron spins. Near the insulator-metal transition caused by heat treatment of ACFs, spin glass-like disordered magnetism observed. Up to an ⁴He coverage of 22.6 μmol/m², no superfluidity is observed due to the strong van der Waals force between ⁴He and nanographite. Over 23.7 μmol/m^{2 4}He coverage, the superfluid transition is observed at approximately T_c ~ 500 mK. Upon increasing the ⁴He coverage, the superfluid density increases, but no change in T_c is observed. These observations indicate that the thickness of superfluid films on nanographite is restricted by the slit type pore shape of ACFs. 

Keywords

Activated carbon fibers (ACFs), nanographite, superfluid helium-4.