Creation and Measurement of Magnetic Charge Currents in Spin Ice

The recent discovery of magnetic charge in spin ice raises the question of whether long-lived currents of magnetic ``monopoles'' can be created and manipulated by applying magnetic fields. Here we show that they can; by applying a magnetic field pulse to a Dy$_2$Ti$_2$O$_7$ spin ice crystal at 0.36 Kelvin, we create a relaxing magnetic current that lasts for several minutes. We measure the current by means of the electromotive force it induces in a solenoid coupled to a susceptometer and quantitatively describe it using a chemical kinetic model of point-like charges obeying the Onsager-Wien mechanism of carrier dissociation and recombination.