Magnetic particle dispersion

1. A magnetic particle dispersion, comprising:

a magnetic particle,

an isothiazoline compound in an amount of 0.001 to 1 part by mass based on 100 parts by mass of the magnetic particle, and

an aqueous medium,

wherein the isothiazoline compound is a compound of formula (1):

wherein R 1 represents a hydrogen atom, or a linear or branched chain hydrocarbon group having 1 to 8 carbon atoms, and R 2 and R 3 each independently represent a hydrogen atom, a halogen atom, or an aliphatic hydrocarbon group having 1 to 12 carbon atoms, in which R 2 and R 3 are optionally bound to each other to form a ring other than a benzene ring, and

wherein the magnetic particle has a first polymer layer having hydrophobicity on the surface of a mother particle and which has a second polymer layer having a glycidyl group, or at least one polar group selected from an amino group, an aldehyde group, a carboxyl group, a tosyl group, a mercapto group, a hydroxyl group, an epoxy group, and an active ester group on at least the surface of the magnetic particle, on the first polymer layer.

2. The magnetic particle dispersion according to claim 1 , wherein when the magnetic particle has a polar group or a ligand, a content of the polar group or the ligand in the magnetic particle is from 0.1 to 100 μmol/g.

3. The magnetic particle dispersion according to claim 1 , wherein when the magnetic particle has a polar group, a parking area of the polar group in the magnetic particle is 2.5 (Å 2 /polar group and ligand) or more.

4. The magnetic particle dispersion according to claim 1 , wherein the magnetic particle has a structure that is optionally hydrolyzed.

5. The magnetic particle dispersion according to claim 1 , wherein a volume average particle size of the magnetic particle is from 0.1 to 10 μm.