Voltage Control of Magnetization Easy-Axes: A Potential Candidate for Spin Switching in Future Ultrahigh-Density Nonvolatile Magnetic Random Access Memory

Abstract

We report a challenging attempt to switch magnetization directions in ferromagnetic films by applying a voltage instead of an external magnetic field. As an example, a voltage control of magnetization easy-axes in a newly developed hybrid system of ferromagnetic/piezoelectric films has been demonstrated by using the well-known effects of both the inverse magnetostriction of ferromagnetic CoPd alloys and the inverse piezoelectricity of lead-zirconate-titanate alloy films. This information-storage and writing method suitable for use in an ultrahigh-density nonvolatile magnetic random access memory may prove to be a new paradigm in information-storage technology.Index Terms-Controllable spin switching, CoPd/PZT hybrid, magnetostrictive effect, piezoelectric effect, voltage control.

Effect of temperature variations and thermal noise on the static and dynamic behavior of straintronics devices

“…14(b), where we simulated Galfenol for different pulsewidths at different temperatures. A lower WEP at higher temperatures is mainly due to the increased h iÀrms from 200 K to 400 K, as expected from (18). B.…”

“…12 for temperature ranges between 200 K and 400 K. As we increase the temperature, the value of h iÀrms increases, leading to easier magnetization flipping and, therefore, a lower delay. The analytical data on the graph are the expected results from (18) and the simulated data are obtained from our Verilog-A model based on the thermally incorporated LLG dynamics in (15)- (17). The accuracy of the developed model can also be confirmed by comparing the analytical and simulated results.…”

“…where C PZT is the capacitance of the piezoelectric layer, DV is the voltage swing across the device, and E d is the dissipated energy due to the Gilbert damping. 61 For the devices with high energy barriers, the critical voltage is high enough it is evident that as the pulsewidth is increased, the WEP decreases dramatically; increasing temperature will also reduce the WEP slightly for a given pulsewidth due to the dependency of the initial angle of temperature in (18).…”

“…To this end, the recently-proposed straintronics principle, a combination of piezoelectricity and magnetostriction, is an alternative approach that overcomes the aforementioned obstacle. [14][15][16][17][18] The amount of charge consumed for switching the MTJ's state in straintronics is well below STT and FIMS. 15,16 Temperature variations can severely impact both static and dynamic responses of straintronics devices.…”

Fabrication of TERFENOL-D/PZT bilayer structures for the study of voltage control of magnetization easy axis

“…This is achieved by a coupling between the inverse piezoelectric effect of the ferroelectric film and the inverse magnetostrictive effect of the magnetic film. This method has the advantage that it can be used for recording information in an ultrahigh density MRAM, since it uses a voltage which can be applied locally to the data bit under consideration [2]. However, since this method depends on the coupling of the magnetostrictive and piezoelectric property, it is believed that the ability to control the direction of magnetization easy axis using an applied voltage, in other words the magnetoelectric effect could be enhanced in bilayer films of TERFENOL-D and PZT as TERFENOL-D is known to be a giant magnetostriction material.…”