Magnetic bead and magnetic bead dispersion

A magnetic bead comprising:

• a magnetic metal powder;
• and
• a coating layer with which a particle surface of the magnetic metal powder is coated, the coating layer being a composite containing silicon and one or more selected from the group consisting of Al, Ti, V, Nb, Cr, Sn, and Zr,
• wherein the coating layer includes a functional group configured to enhance binding of a biological substance to the magnetic bead, the functional group being selected from the group consisting of an OH group, an epoxy group, a trimethylsilyl group, and a NHS group,
• an average particle size D50 of the magnetic bead is 0.5 μm or more and 50 μm or less,
• a ratio D90/D50 of a 90% particle size D90 in a particle size distribution of the magnetic bead to the average particle size D50 is 2.00 or less, and
• when the magnetic bead is left to stand in a state of a dispersion obtained by dispersing the magnetic bead in water, a time until an initial absorbance of the dispersion attenuates to 80% of an absorbance when the standing is started is 90 seconds or longer.