As a next-generation nonvolatile memory substituting for a flash memory or the like which has come to have a limit in miniaturization, a resistance change memory for storing data by using a resistance variable element, such as MRAM (Magnetoresistive Random Access Memory), ReRAM (Resistance Random Access Memory), PCRAM (Phase Change Random Access Memory), and the like has attracted attention.
As a method of increasing the memory density (increasing capacity), there is a method of reducing the size of the elements constituting the memory, as well as a method of multileveling the recording bits per element constituting the memory, and various multileveling methods have been proposed (for example, see Patent Documents 1 to 3).
There is one type of MRAM called a magnetic wall driving type or a magnetic wall shifting type (for example, see Patent Document 4). The magnetic wall driving MRAM allows current to flow in an in-plane direction of a magnetic wall driving layer (or magnetization free layer), shifts the magnetic wall by the spin transfer effect of spin polarized electrons, and reverses the magnetization direction of the ferromagnetic film according to the direction of the write current and writes data.
Patent Document 4 describes a method of multilevel recording and analog recording with respect to a magnetic wall driving MRAM.
In MRAM, different writing methods of data have been proposed, and in addition to a magnetic wall driving MRAM, a magnetic field writing MRAM, a yoke magnetic field writing MRAM, an STT (Spin Transfer Torque) MRAM, an SOT (Spin Orbit Torque) MRAM, and the like are known.