Composition and heat transport device

A composition comprising a particle and an aqueous medium including water, wherein

• the particle contains a magnetic particle and a dispersant including polyacrylic acid or a salt thereof;
• and
• the composition decreases magnetization with an increase in temperature within a temperature range of 0° C. to 100° C., and increases magnetizaton with a decrease in temperature within the above temperature range,
• wherein the dispersant has a weight average molecular weight of a range of 3000 to 20000,
• wherein the magnetic particle is a manganese zinc ferrite particle represented by formula (1):
• (MnO)x·(ZnO)y·(Fe2O3)z Formula (1)
• in formula (1), x, y, and z satisfy 0.15≤x≤0.40, 0.10≤y≤0.25, 0.48≤z≤0.60, and x+y+z=1;
• and at least one compound selected from the group consisting of SrO, NiO, MgO, and CaO is further added to formula (1) at a ratio of 0.01 to 0.10.