Demonstration of a pseudo-magnetization based simultaneous write and read operation in a Co60Fe20B20/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructure

Abstract

Taking advantage of the magnetoelectric and its inverse effect, this article demonstrates strainmediated magnetoelectric write and read operations simultaneously in co 60 fe 20 B 20 /pb(Mg 1/3 nb 2/3) 0.7 ti 0.3 o 3 heterostructures based on a pseudo-magnetization µ ≡ m x 2 − m y 2. By applying an external DC-voltage across a (011)-cut PMN-PT substrate, the ferroelectric polarization is reoriented , which results in an anisotropic in-plane strain that transfers to the CoFeB thin film and changes its magnetic anisotropy H k. The change in H k in-turn results in a 90° rotation of the magnetic easy axis for sufficiently high voltages. Simultaneously, the inverse effect is employed to read changes of the magnetic properties. The change of magnetization in ferromagnetic (FM) layer induces an elastic stress in the piezoelectric (PE) layer, which generates a PE potential that can be used to readout the magnetic state of the FM layer. The experimental results are in excellent qualitative agreement with an equivalent circuit model that considers how magnetic properties are electrically controlled in such a PE/FM heterostructure and how a back-voltage is generated due to changing magnetic properties in a self-consistent model. We demonstrated that a change of easy axis of magnetization due to an applied voltage can be directly used for information processing, which is essential for future ME based devices. Recently, so-called Magnetoelectric (ME) effects 1-4 in piezoelectric (PE)/FerroMagnetic (FM) structures have attracted substantial research interest, since these may open a path towards controlling magnetic properties by means of an electric field-rather than currents-to achieve low energy dissipation in the writing process of magnetic memory cells 5-22. As to the reading process, the Giant Magneto-Resistance (GMR) 18 or Tunneling Magneto-Resistance (TMR) 1 is usually utilized to readout the stored magnetic information. However, the readout energy based on magneto-resistive methods is not negligible compared with the extremely low writing energies. In addition, the integration of GMR or Magnetic Tunnel Junction (MTJ) stacks with piezoelectric substrates remains a challenge. This raises the question whether voltages that are used in case of the write operation could also be used in a reverse configuration to read the magnetic information in a more power efficient way. To demonstrate this idea, in this article, we have measured the reciprocal ME effect simultaneously and achieved a strain-mediated magnetoelectric write and read unit in a Co 60 Fe 20 B 20 /Pb(Mg 1/3 Nb 2/3) 0.7 Ti 0.3 O 3 heterostructure based on a pseudo-magnetization µ ≡ m x 2-m y 2 rather than a net magnetization m x , m y or m z. Single crystal PMN-PT with (011) orientation was employed in this work as the piezoelectric substrate for achieving large ME effects due to its large piezoelectric coefficients with d 31 ~ −3,100 pC/N along the [100] direction and d 32 ~ 1,400 pC/N along the [01-1] direction 23-29. The write operation in the magnetic subsystem...