Figure 1: The principle of the multilevel nonvolatile memory.

(a–d) The schematic of a memory cell showing different states of the ME coefficient α. When the direction of M remains unchanged, the value of α depends on the ratio of up and down ferroelectric domains, ranging from positive to negative. (e) The illustration of reading operation. An independent reading coil generates a small ac magnetic field ΔH and the stored information is read out by measuring the induced voltage ΔV. All the memory cells can share a single reading coil, which greatly simplifies the fabrication and operations of the memory device.