Ferrofluid is a colloidal liquid with magnetic particles suspended in carrier fluid. Typical composition is 5% magnetic solids, 10% surfactant, 85% carrier. Particles are coated with surfactants to prevent clumping
Ferrotec has been supplying ferrofluid to audio speakers since 1970s. Company has laboratories in US and Japan for fluid development
Compass shows cardinal directions using magnetized needle aligned with Earth's magnetic field. North corresponds to 0°, east to 90°, south to 180°, west to 270°. Magnetic compass points to magnetic north, approximately 1,000 miles from true north
MRI was invented in 1977 as a medical imaging technique. MRI uses powerful magnets and radio waves to capture internal body structures. Modern hospitals operate MRI scanners at 0.5 to 3 Tesla
Compass invented by ancient Chinese during Han dynasty (202 BC-220 AD). First used for geomancy and fortune-telling, later adapted for navigation. Lodestone was used to create early compasses
Magnetite (Fe3O4) is a common iron oxide mineral in the spinel group. Contains variable amounts of Al, Cr, Mn3+, and Ti4+ substituting for Fe3+. Forms crystals with specific gravity 5.20 and hardness 6 on Mohs scale