magnetic susceptibility

A magnet weighing just a few grains of sand hovers in midair with no support. It doesn't touch the walls, doesn't rub against bearings — it just hangs in a magnetic trap like a speck of dust in a sunbeam. Researchers have turned this tiny object into an ultra-sensitive compass: the device detects changes in the magnetic field of 23 femtotesla.

A pendulum weighing a few grains of sand swings on a hair-thin glass fiber. Its motions are so faint that the thermal jostling of air molecules seems like a hurricane. Yet such a pendulum is the key to witnessing quantum wonders in the world of large objects.

A magnet, like a compass needle, likes to point in a certain direction. But what if the material is layered, like a stack of pancakes? Scientists took just such a magnet made from a compound of chromium, germanium, and tellurium and set out to find out how stubbornly it resists having its magnetization turned.

A dust grain in interstellar space is like a tiny compass. Inside it sit inclusions of magnetic minerals that make the grain rotate along invisible magnetic field lines. How obediently the grains align determines how they polarize the light of distant stars and what radiation they emit.

A glass of solidified glass may seem motionless, but inside, the atoms are frozen in random positions, never having found perfect order. A similar situation occurs in spin glasses: the magnetic moments of atoms freeze, pointing in different directions, and the material loses the ability to be simply magnetized.

Two pieces of graphite rub against each other, and the resistance vanishes as if an invisible film of oil separated them. Previously, this was only seen under a microscope, on tiny contact patches.