An ordinary magnetic compass freezes when lightning strikes nearby. A sudden jump in the magnetic field throws the needle off. A similar problem has been hindering scientists trying to measure magnetism in strong pulsed fields: those that switch on for a thousandth of a second.
The new setup tackles this with a laser beam. The beam reflects off the sample's surface, and the rotation of the light's polarization plane (the Kerr effect) reveals the magnetization. The field reaches 13.1 tesla — hundreds of thousands of times stronger than Earth's field. The instrument captures a full magnetic hysteresis loop in a single pulse.
The test was run on a magnetite crystal (Fe3O4)—the very mineral from which ancient Chinese made the first compass. The pulsed measurements matched the steady-state ones within error. Then the method was tried on various grades of industrial permanent magnets — again yielding clean loops.
Now a material's magnetic signature can be captured in seconds, not hours. That will speed up the hunt for new alloys for electric vehicles, wind turbines, and sensors. Once again, the laser has outrun the compass.
The 13.1 tesla field in the new setup is 260,000 times stronger than Earth's magnetic field. In such a field, an ordinary iron nail would be pulled with enough force to lift a small car.