Compared with current-controlled magnetization switching in a perpendicular magnetic tunnel junction (MTJ), electric field-or voltage-induced magnetization switching reduces the writing energy of the memory cell, which also results in increased memory density. In this work, an ultrathin PZT film with high dielectric constant was integrated into the tunneling oxide layer to enhance the voltage-controlled magnetic anisotropy (VCMA) effect. The growth of MTJ stacks with an MgO/PZT/MgO tunnel barrier was performed using a combination of sputtering and atomic layer deposition techniques. The fabricated MTJs with the MgO/PZT/MgO barrier demonstrate a VCMA coefficient, which is $40% higher (19.8 6 1.3 fJ/V m) than the control sample MTJs with an MgO barrier (14.3 6 2.7 fJ/V m). The MTJs with the MgO/PZT/MgO barrier also possess a sizeable tunneling magnetoresistance (TMR) of more than 50% at room temperature, comparable to the control MTJs with an MgO barrier. The TMR and enhanced VCMA effect demonstrated simultaneously in this work make the MgO/PZT/MgO barrier-based MTJs potential candidates for future voltagecontrolled, ultralow-power, and high-density magnetic random access memory devices.

In this manuscript, we examine ways to create multiferroic composites with controlled nanoscale architecture. We accomplished this by uniformly depositing piezoelectric lead zirconate titanate (PZT) into templated mesoporous, magnetostrictive cobalt ferrite (CFO) thin films to form nanocomposites in which strain can be transferred at the interface between the two materials. To study the magnetoelectric coupling, the nanostructure was electrically poled ex situ prior to magnetic measurements. No samples showed a change in in-plane magnetization as a function of voltage due to substrate clamping. Out-of-plane changes were observed, but contrary to expectations based on total PZT volume fraction, mesoporous CFO samples partially filled with PZT showed more change in out-of-plane magnetization than the sample with fully filled pores. This result suggests that residual porosity in the composite adds mechanical flexibility and results in greater magnetoelectric coupling.

This manuscript examines the mechanism of strain-coupling in a multiferroic composite of mesoporous cobalt ferrite (CFO), conformally filled with lead zirconate titanate (PZT). We find that when the composites are electrically poled, remanent strain from the piezoelectric PZT layer can be transferred to the magnetostrictive CFO layer. X-ray diffraction shows that this strain transfer is greatest in the most porous samples, in agreement with magnetometry measurements, which show the greatest change in sample saturation magnetization in the most porous samples. Strain analysis shows that porosity both accommodates greater lattice strain and mitigates the effects of substrate clamping in thin film strain-coupled composites.

A dense, homogeneous and crack-free ferroelectric PZT thin film with h100i-preferred orientation was produced using the sol-gel method. The volume fraction a (100) of h100i-oriented grains in the PZT film was calculated [a (100) % 80%] from XRD of the PZT thin film and powder. The PZT thin film exhibits an open polarization vs. electric field loop and a low leakage current density from 10 À8 A/cm 2 to 10 À7 A/cm 2. The electrical conduction data were fit to a Schottky-emission model with deep traps from 100 kV/cm to 250 kV/cm. A modified capacitance model was introduced that adds electrical domain capacitance based on a metal-ferroelectric-metal (MFM) system with Schottky contacts. The model reproduces the observed non-linear capacitance vs. voltage behavior of the film. V

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