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Magnetic piezoelectric composite, sensor, and memory

NIST developed a Cobalt-Nickel multilayer with strong perpendicular magnetization that is suitable for growth on piezoelectric PZT. Strain mediated by the PZT can modulate the magnetic coercivity by over 30 %, a promising benchmark for strain- tuneable perpendicular magnetization. A strong perpendicular magnetic anisotropy field is "good" because it ensures that for technologies based on encoding digital information in the magnetic orientation, thermal energy from the environment cannot disturb the encoded data. On the other hand, this strength is also a problem, because it requires large energy to rewrite data encoded in the magnetization orientation of a particular "domain" in the (say, change a '1' to a 'O' or vice-versa).

Finding new ways to reduce the energy cost to write data on high anisotropy magnetic materials has motivated NIST to search for the best combination of ferromagnetic thin film with piezoelectric substrate. This invention uses a voltage applied through the thickness of a Pb(Zr,Ti)03 (PZT) slab to generate compressive and/or tensile strains in the two lateral directions orthogonal to the thickness. Voltage-generated strains in the PZT apply corresponding stresses to the magnetic film that has been grown directly on top of the slab. Lateral strains resulting from these stresses
modify the magnetic coercivity of the Co-Ni film by up to 30%. This can be used to lower the energy required to reverse the magnetization.

Cobalt-Nickel multilayer is a new and useful improvement on previous embodied hybrids between ferromagnets and piezoelectrics and is the first time that such a multilayered film has been proposed and proven to grow on a functional piezoelectric substrate.

The figure below shows a flow chart process for making a magnetic piezoelectric composite.


This NIST invention is a cobalt-nickel multilayer material with strong perpendicular magnetization that is suitable for growth on piezoelectric PZT. Strain mediated by the PZT can modulate the magnetic coercivity by more than 30%. Applying strains from a piezoelectric material into a ferromagnet is a promising method for controlling a ferromagnet's magnetization without applied external magnetic fields. By applying a voltage to a piezoelectric actuator, changes in the surface strain of the actuator can be partially transferred into the ferromagnet. This method has been investigated by using piezoelectric actuator plates as the surfaces upon which to grow a variety of Cobalt and Iron based magnetic films. Cobalt-Nickel multilayers exhibit desirable properties for many magnetic sensors and data storage applications, but until now have never been implemented as part of a piezoelectric/ferromagnetic bilayer. Additionally, the Cobalt-Nickel multilayers has characteristics favorable for next generation random access memory (RAM), strain-sensing devices, and used in small sensors for strain and pressure. Technology for RAM continues to move forward and thus command the need for this material in future generations of magnetic memories.

The invention is a material that could potentially be used in magnetic random access memory (RAM) or in small sensors for strain, pressure etc.; the present invention is only one possible


Daniel Gopman, Robert Shull

Patent Number: 
Technology Type(s): 
Advanced Manufacturing Processes, Analytical Chemistry, Manufacturing, Materials for Electronics, Biochemical Science, Chemical Sciences, Electromagnetics, Electronics,
Internal Laboratory Ref #: 
Patent Issue Date: 
April 24, 2018
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