Magnetic Tunnel Junction Devices Research Articles

Plasma–induced damage in magnetic tunneling junctions

Plasma–induced damage (PID) in the fabrication of magnetic tunnel junction (MTJ) based magnetic random access memory (MRAM) is studied after the formation of MTJ devices, which excludes process effect directly from the ion beam etching and protection layer deposition. Large degradation in coercivity (Hc) of MTJs is found in comparison with that measured just after the top metal （TM） was formed, which heavily deteriorates MRAM performances. This Hc degradation is found to be mainly introduced in plasma-enhanced chemical vapor deposition (PECVD) for passivation (PA) film after TM formation. The amplitude of the degradation depends on plasma power, but independent of the composition of the PA film. Hc reduction is observed once the plasma is turned on even though no PA deposition is performed. These results suggest that the observed Hc degradation is from PID effect most likely due to the plasma charge damage (PCD) induced in the PECVD process as no direct plasma contact with MTJ devices is involved in the process. It is argued that this PCD effect is due to the charge accumulations at the interface between the free layer and MgO barrier based on electric field–modulated magnetic anisotropy effect. This is further confirmed by an experiment in which Hc degradation is largely cured through partially removing the trapped charges by an annealing process.

A novel magnetic tunnel junction fabricated by robust intrinsic van der Waals half-metals

Two-dimensional magnetic van der Waals materials (vdW) have attracted considerable attentions in recent years due to their emerging physical properties and great potential application to the spintronics devices. Magnetic tunnel junction (MTJ) is one of the most important devices in spintronics. However, many unknown mechanisms governing its critical performance remain to be elucidated. Here, based on first-principles calculations, vdW materials VBr3 and VCl3 are shown to be the robust intrinsic half-metals with spin down electron's energy gap about 3.3 eV, and the Fermi level is almost located at the center of the spin down electron's energy gap. Based on this, we predict that application of VBr3 to the magnetic electrodes of MTJ would greatly improve the off/on ratio of junction resistance. Moreover, the coercivity of magnetic electrodes used by vdW material VBr3 can be tuned by the number of layers, and an antiferromagnetic layer pinning the ferromagnetic electrode can be omission. This provides a reliable way to study and design the MTJ devices in the future.

Nanoscale Thermal Transport Model of Magnetic Tunnel Junction (MTJ) Device for STT-MRAM

Spin-transfer-torque magnetic random access memory (STT-MRAM) based on magnetic tunnel junction (MTJ) device has attracted significant attention from academics and industries. Nevertheless, the thermal effect under bias operation affects the overall performance and stability of a device. To evaluate the thermal phenomenon in MTJ devices accurately, the non-equilibrium effect between the electron and the phonon near the electrode-barrier interface cannot be ignored. The existence of the interface leads to additional thermal resistance hindering the heat conduction of tunnel junction. Therefore, an effective equivalent model concerning the interface effect is necessary to represent the heat transportation of the device. In this article, a nanoscale thermal transport model of the MTJ device is proposed. The influence of the thermal conductivity of the nano-oxide layer on the temperature distribution is discussed. The interface energy balance transport model is used to clarify the non-equilibrium relationship between the phonon and the electron at the CoFeB/MgO/CoFeB interfaces. A parameterization study is conducted to illustrate the temperature distribution in the nanoscale thermal transport model. Furthermore, the phonon-electron coupling distance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\delta$ </tex-math></inline-formula> ) based on the thermal conductivity of the phonon ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa _{p}$ </tex-math></inline-formula> ) and the electron ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa _{e}$ </tex-math></inline-formula> ) of the device is implemented to construct the effective equivalent model using finite element modeling (FEM), which could realistically reflect the thermal transport under working conditions. The established equivalent model has a guiding role in exploring the thermal transportation in the nanoscale MTJ device.

Compact Model of Domain Wall MTJ Driven by Spin Orbit Torque and Dzyaloshinskii–Moriya Interaction

Current-induced domain wall motion (CIDWM) shows promising prospects with low power, high density, high speed, and so on. Recent studies have demonstrated that magnetic tunnel junction (MTJ) based on CIDWM has great potential in mimicking a non-volatile artificial neuron and synapse. By combining the effect of the interfacial Dzyaloshinskii–Moriya interaction (DMI) to stabilize the Néel-type domain wall (DW) and the high-speed low-power advantages of spin orbit torque (SOT), the novel MTJ device is experimentally demonstrated with low threshold current and high propagation speed, which shows potential applications in the field of the artificial neuron and synapse. In this article, a compact model for CIDWM-MTJ based on SOT and DMI is presented. The model integrates the SOT mechanism for magnetization reversal and DW nucleation, CIDWM behaviors, and tunnel resistance theory of MTJ nanopillar. The micromagnetic simulation and the temporal evolution of the DW position are implemented by solving the Landau–Lifshitz–Gilbert (LLG) equation and the 1-D model. Based on the developed model, a hybrid CIDWM-MTJ/CMOS circuit is simulated for verification. The presented model combines the CIDWM dynamics and the MTJ magnetic dynamics, showing potential application for the simulation of all-spin artificial neural network (ANN).

Time-Division Multiplexing Ising Computer Using Single Stochastic Magnetic Tunneling Junction

A magnetic tunneling junction (MTJ) with very low energy barrier, which shows controllable stochastic property, is recently proposed to constitute the probability bit (P-Bit). With the P-Bit, Ising computation, which is a general and powerful computing platform for both conventional and non-conventional problems, is implemented. However, such hardware emulation suffers from the severe intrinsic variations of a stochastic MTJ device. The nonuniform probability switching curves of different stochastic MTJs hinder straightforward expansion of Ising computer to a large P-Bits array for solving more complicated problems. In this work, we propose a novel Ising computer using a single stochastic MTJ device. With the utilization of the time-division multiplexing (TDM) technology, a “Compute–Read–Switch” scheme is proposed, so that the single stochastic MTJ can act as multiple P-Bits during Ising computation. A design guide for the current magnitude and time duration of the “Compute–Read–Switch” scheme is investigated and provided. Furthermore, NOT and XOR logic gates are implemented with our proposal. An accuracy rate as high as 69% for the integer factorization is also achieved, which is comparable with conventional Ising computer. Meanwhile, the TDM Ising computer avoids the calibration process, which is mandatory in the conventional Ising computer.

Demonstration of in-plane magnetized stochastic magnetic tunnel junction for binary stochastic neuron

A binary stochastic neuron (BSN) or a probabilistic bit (p-bit) randomly fluctuates between digitized “0” and “1” with a controllable functionality of time-averaged value. Such an unconventional bit is the most essential building block for the recently proposed stochastic neural networks and probabilistic computing. Here, we experimentally implement a magnetic tunnel junction (MTJ) for BSN, with relaxation times on the order of tens of milliseconds that can be modulated by a current-induced spin-transfer torque. The NIST Statistical Test Suite (800-22a) is used to verify true random number generation by the BSN-MTJ device. Our results suggest the possibility of using the artificial BSN MTJ device in neuromorphic applications as well as in a recently proposed probabilistic computing.

Computational delving into conceivable thermoelectric and spintronic applications of NH4AF3 (A = Fe and Co) ferromagnets

In this investigation, the structural, mechanical, electronic, magnetic, and thermoelectric properties of fluoroperovskite NH4AF3 (A = Fe and Co) compounds were determined utilizing the WIEN2k code. The structural properties such as tolerance factor, enthalpy, and elastic stability criterion predict that the studied compounds are mechanically and thermodynamically stable. Furthermore, the mechanical properties show that NH4FeF3 is more stretchable and rigid in nature than NH4CoF3. Interestingly, both compounds exhibit the anisotropic, intermediate type of bonding effect, higher plastic deformation limit, and brittle nature. The high melting temperature of the present compounds indicates the possible usage of these compounds in high-temperature electronic applications. The electronic calculations show that NH4FeF3 and NH4CoF3 are half-metallic and ferromagnetic compounds with a combination of ionic and covalent bonds between the different atoms. The thermoelectric parameters predict that electrons are the main charge carriers for the present compound with p-type character. Our study suggests that these plausible applications of the compounds are very versatile and include heat sensors, spintronic devices, optoelectronic sensors, and magnetic tunnel junction devices.

Picosecond optospintronic tunnel junctions

Significance Spintronic devices have become promising candidates for next-generation memory architecture. However, state-of-the-art devices, such as perpendicular magnetic tunnel junctions (MTJs), are still fundamentally constrained by a subnanosecond speed limitation, which has remained a long-lasting scientific obstacle in the ultrafast spintronics field. The highlight of our work is the demonstration of an optospintronic tunnel junction, an all-optical MTJ device which emerges as a new category of integrated photonic–spintronic memory. We demonstrate 1) laser-induced deterministic and efficient writing by an all-optical approach and electrical readout by tunnel magnetoresistance, 2) writing speed within 10 ps, demonstrated by femtosecond-resolved measurements, and 3) integration with state-of-the-art MTJ performance and a complementary metal–oxide–semiconductor-compatible fabrication progress.

Smart Material Implication Using Spin-Transfer Torque Magnetic Tunnel Junctions for Logic-in-Memory Computing

Smart material implication (SIMPLY) logic has been recently proposed for the design of energy-efficient Logic-in-Memory (LIM) architectures based on non-volatile resistive memory devices. The SIMPLY logic is enabled by adding a comparator to the conventional IMPLY scheme. This allows performing a preliminary READ operation and hence the SET operation only in the case it is actually required. This work explores the SIMPLY logic scheme using nanoscale spin-transfer torque magnetic tunnel junction (STT-MTJ) devices. The performance of the STT-MTJ based SIMPLY architecture is analyzed by varying the load resistor and applied voltages to implement both READ and SET operations, while also investigating the effect of temperature on circuit operation. Obtained results show an existing tradeoff between error rate and energy consumption, which can be effectively managed by properly setting the values of load resistor and applied voltages. In addition, our analysis proves that tracking the temperature dependence of the MTJ properties through a proportional to absolute temperature (PTAT) reference voltage at the input of the comparator is beneficial to mitigate the reliability degradation under temperature variations.

Improving signal-to-noise ratio of magnetic tunnel junction based radio frequency detector via spin-torque ferromagnetic resonance.

This article focuses on the spin-torque ferromagnetic resonance (STFMR) technique, which was developed and optimized to investigate spin-transfer effects in magnetic tunnel junctions (MTJ) and spin Hall effect phenomena in ferromagnet/non-magnetic heavy metal bilayer systems. The devices for STFMR are typically fabricated with co-planar waveguides with contact pads for applying radio frequency or direct current, Irf(Idc). The device under investigation was a CoFeB/MgO/CoFeB based MTJ with a resistance-area product of 1.5 Ω (μm)2 having a circular cross section with a diameter of 180nm and tunneling magneto-resistance in the range of 60%-80%. The development of the STFMR setup and its optimization for achieving higher signal-to-noise ratio (SNR) is discussed using two modulation schemes, namely, radio-frequency modulation and field modulation (FM). The FM-STFMR method reduces frequency-dependent noise and offers a higher SNR of 30 dB compared to other modulation schemes in the literature. In addition, a vector network analyzer based STFMR technique is developed, which provides a simple and fast means for characterizing MTJ devices. Furthermore, to calculate the exact power reaching the MTJ, impedance mismatch is calculated using the de-embedding method. The magnitude of in-plane torkance and out-of-plane torkance with dc bias is measured, and the results are found to be consistent with the results of STFMR techniques. The results show that the magnitude of out-of-plane torkance is substantially smaller than that of in-plane torkance in MTJ.

Progress toward picosecond on-chip magnetic memory

We offer a perspective on the prospects of ultrafast spintronics and opto-magnetism as a pathway to high-performance, energy-efficient, and non-volatile embedded memory in digital integrated circuit applications. Conventional spintronic devices, such as spin-transfer-torque magnetic-resistive random-access memory (STT-MRAM) and spin–orbit torque MRAM, are promising due to their non-volatility, energy-efficiency, and high endurance. STT-MRAMs are now entering into the commercial market; however, they are limited in write speed to the nanosecond timescale. Improvement in the write speed of spintronic devices can significantly increase their usefulness as viable alternatives to the existing CMOS-based devices. In this article, we discuss recent studies that advance the field of ultrafast spintronics and opto-magnetism. An optimized ferromagnet–ferrimagnet exchange-coupled magnetic stack, which can serve as the free layer of a magnetic tunnel junction (MTJ), can be optically switched in as fast as ∼3 ps. Integration of ultrafast magnetic switching of a similar stack into an MTJ device has enabled electrical readout of the switched state using a relatively larger tunneling magnetoresistance ratio. Purely electronic ultrafast spin–orbit torque induced switching of a ferromagnet has been demonstrated using ∼6 ps long charge current pulses. We conclude our Perspective by discussing some of the challenges that remain to be addressed to accelerate ultrafast spintronics technologies toward practical implementation in high-performance digital information processing systems.

Electrical Manipulation of Exchange Bias in an Antiferromagnet/Ferromagnet‐Based Device via Spin–Orbit Torque

AbstractElectrical manipulation of exchange bias (EB) enables an additional degree of freedom in the design of innovative spintronic devices. However, the electrical switching of EB via spin–orbit torque (SOT) has not been achieved in magnetic tunnel junctions (MTJs), which are one of the building blocks in spintronic devices. Herein, based on the SOT in antiferromagnets (AFMs), perpendicular EB reversal across AFM IrMn and ferromagnetic (FM) [Co/Pt]2 multilayer is demonstrated both in extended and confined geometries. In particular, in three‐terminal perpendicular MTJ devices, the switching of the EB using the SOT is achieved. Both high and low resistances are observed at the zero magnetic field during EB switching. The findings provide the direction to include a new functionality in spintronic devices and will inspire future research in exploring the electrical control of EB in SOT magnetic random access memory (SOT‐MRAM).

Strontium Ferromolybdate-Based Magnetic Tunnel Junctions

Thin-film strontium ferromolybdate is a promising material for applications in room-temperature magnetic tunnel junction devices. These are spin-based, low-power-consuming alternatives to CMOS in non-volatile memories, comparators, analog-to-digital converters, and magnetic sensors. In this work, we consider the main tasks to be solved when creating such devices based on strontium ferromolybdate: (i) selecting an appropriate tunnel barrier material, (ii) determining the role of the interface roughness and its quantification, (iii) determining the influence of the interface dead layer, (iv) establishing appropriate models of the tunnel magnetoresistance, and (v) promoting the low-field magnetoresistance in (111)-oriented thin films. We demonstrate that (i) barrier materials with a lower effective electronegativity than strontium ferromolybdate are beneficial, (ii) diminution of the magnetic offset field (the latter caused by magnetic coupling) requires a wavy surface rather than solely a surface with small roughness, (iii) the interface dead-layer thickness is of the order of 10 nm, (iv) the tunnel magnetoresistance deteriorates due to spin-independent tunneling and magnetically disordered interface layers, and (v) antiphase boundaries along the growth direction promote the negative low-field magnetoresistance by reducing charge carrier scattering in the absence of the field.

High-Accuracy Spintronic Approximate Compressors for Error-Resilient In-Memory Computing

With transistors reaching nanometer dimensions, dissipated energy has become of great importance in recent years. A practical approach to reducing energy consumption is to use logic-in-memory (LIM) structures based on magnetic tunnel junction (MTJ) devices combined with approximate computing. In this paper, we propose energy-efficient MTJ/FinFET-based approximate 5:2 compressors for error-resilient in-memory computing, providing an accuracy close to the exact design (1.54% error rate) while reducing the energy consumption by more than 50%. The innovative Boolean equations and the structure of the proposed approximate circuits based on spin-Hall effect assisted MTJs lead to a significantly more effective compromise between energy and accuracy than the previous exact and approximate counterparts. The simulation results provided using HSPICE with 7[Formula: see text]nm FinFETs and SHE-assisted MTJ models demonstrate the superior hardware parameters of the proposed designs. Furthermore, the MATLAB simulations show an average peak signal-to-noise ratio (PSNR) of more than 43 and an average structural similarity index metric (SSIM) of more than 0.99 across image multiplication, sharpening, and smoothing operations.

All-Electrical Control of Compact SOT-MRAM: Toward Highly Efficient and Reliable Non-Volatile In-Memory Computing.

Two-dimensional van der Waals (2D vdW) ferromagnets possess outstanding scalability, controllable ferromagnetism, and out-of-plane anisotropy, enabling the compact spintronics-based non-volatile in-memory computing (nv-IMC) that promises to tackle the memory wall bottleneck issue. Here, by employing the intriguing room-temperature ferromagnetic characteristics of emerging 2D Fe3GeTe2 with the dissimilar electronic structure of the two spin-conducting channels, we report on a new type of non-volatile spin-orbit torque (SOT) magnetic tunnel junction (MTJ) device based on Fe3GeTe2/MgO/Fe3GeTe2 heterostructure, which demonstrates the uni-polar and high-speed field-free magnetization switching by adjusting the ratio of field-like torque to damping-like torque coefficient in the free layer. Compared to the conventional 2T1M structure, the developed 3-transistor-2-MTJ (3T2M) cell is implemented with the complementary data storage feature and the enhanced sensing margin of 201.4% (from 271.7 mV to 547.2 mV) and 276% (from 188.2 mV to 520 mV) for reading “1” and “0”, respectively. Moreover, superior to the traditional CoFeB-based MTJ memory cell counterpart, the 3T2M crossbar array architecture can be executed for AND/NAND, OR/NOR Boolean logic operation with a fast latency of 24 ps and ultra-low power consumption of 2.47 fJ/bit. Such device to architecture design with elaborated micro-magnetic and circuit-level simulation results shows great potential for realizing high-performance 2D material-based compact SOT magnetic random-access memory, facilitating new applications of highly reliable and energy-efficient nv-IMC.

Novel ESD device design for STT-MRAM memory chip

An investigation of the influence of the magnetic field induced by electrostatic discharge (ESD) current on magnetic tunnel junction (MTJ) device is presented in the paper. The transient magnetic field generated by the ESD current is not considered in the traditional CMOS ESD protection strategy, which may be a reason of the degradation of the performance and the robustness of STT-MRAM. An ESD protection circuit of STT-MRAM is proposed in the paper, including the diode-based ESD devices, the filter circuit and the power clamp. Based on the waveform analysis of the three ESD standard test models, including HBM, MM and CDM, a filter circuit is added in the ESD device to decrease the influence of the high frequency components on the magnetic device. The diode-based ESD devices are integrated in the ESD structure, which is used for the ESD window of STT-MRAM for its low operating voltage. Based on the operation mechanism of the STT-MRAM, its ESD window allows a low operating voltage, thus the diode-based devices are chosen to be integrated in the ESD device. The distribution and magnitude of the magnetic field are studied in the paper. The results show that the ESD protection circuit of STT-MRAM can effectively suppress the magnetic field generated by the ESD current, hence increasing the stability of STT-MRAM. Under the influence of the HBM, MM and CDM events, the ESD disturbance probability of the MTJ device are 2.0 × 10−12, 5.8 × 10−9 and 1.1 × 10−12 respectively. The influence of the memory density and the distance between pads and memory array are also investigated in this paper. The ESD protection strategy proposed in the paper can be adopted for the future high performance STT-MRAM.

MPT Tool: A Parameter Extraction Tool for Accurate Modeling of Magnetic Tunnel Junction Devices

Until now, many models of magnetic tunnel junction (MTJ) devices have been reported in the literatures, which are very helpful for behavior simulations in spintronic circuit design and simulation. However, there are few reports on how to obtain the accurate modeling parameters, as well as the accurate simulation of the complete flow from device parameters to device modeling and hybrid MTJ/CMOS circuits. One of the difficulties in obtaining the accurate MTJ modeling results is the lack of experimental parameters. The parameters in the MTJ models should be precisely identified to obtain accurate simulation results. However, in the reported models, many parameters are theoretically set instead of actual extraction. In this paper, a parameter extraction tool, named MPT tool, is proposed for the accurate modeling of the MTJ devices. In the MPT tool, the measured results of the MTJ devices are adopted as the input. There are two main functions of the MPT tool. One is the parameter extraction based on the input experimental results. The other is the parameter optimization based on the specific algorithm. In the tool, the simulated annealing (SA) optimization algorithm is applied to optimize the extracted parameters. The parameters of the extraction procedure and the modeling results based on the parameters of the optimization procedure are compared with the experimental data, respectively. The proposed extraction procedure and the optimization procedure together with the adopted MTJ model is as an efficient approach to improve the accuracy of the simulation result.

MagCiM: A Flexible and Non-Volatile Computing-in-Memory Processor for Energy-Efficient Logic Computation

This paper presents a high-performance and energy efficient processor exploiting a <u>Mag</u>netoresistive-based <u>C</u>omputing-<u>i</u>n-<u>M</u>emory array architecture (so-called MagCiM processor), to perform Boolean logic functions on operands stored in a memory array. The proposed processor efficiently addresses the memory wall and the leakage power consumption problems in conventional processors. The MagCiM processor utilizes mCell memory, a class of Magnetoresistive memory employing only Magnetic Tunnel Junction (MTJ) devices, to realize both computation-in-memory and on-chip instruction and data memories. The mCell memory is characterized by almost zero leakage power, high integration density, high level of reliability, and compatibility with the CMOS VLSI fabrication process. The circuit-level simulation results through comparisons with the previous work reveal that the MagCiM processor provides low occupation area, low power, and energy consumption and offers Normally-off instant-on computing capability, which makes it very suitable for embedded system applications. Based on our evaluations, a conventional processor based on the well-known MIPS architecture consumes about 13 times more energy while having 1.5 times more delay than the MagCiM processor.

Process deviation based electrical model of spin transfer torque assisted voltage controlled magnetic anisotropy magnetic tunnel junction and its application

As one of the key components in the non-volatile full adder (NV-FA), spin transfer torque assisted voltage controlled magnetic anisotropy magnetic tunnel junction (STT assisted VCMA-MTJ) will possess superior development prospects in internet of things, artificial intelligence and other fields due to its fast switching speed, low power consumption and good stability. However, with the downscaling of magnetic tunnel junction (MTJ) and the improvement of chip integration, the effects of process deviation on the performances of MTJ device as well as NV-FA circuit become more and more important. Based on the magnetization dynamics of STT assisted VCMA-MTJ, a new electrical model of STT assisted VCMA-MTJ, in which the effects of the film growth variation and the etching variation are taken into account, is established to study the effects of the above deviations on the performances of MTJ device and NV-FA circuit. It is shown that the MTJ state fails to be switched under the free layer thickness deviation &lt;i&gt;γ&lt;/i&gt;&lt;sub&gt;tf&lt;/sub&gt; ≥ 6% or the oxide layer thickness deviation &lt;i&gt;γ&lt;/i&gt;&lt;sub&gt;tox&lt;/sub&gt; ≥ 0.7%. The sensing margin (SM) is reduced by 17.5% as the tunnel magnetoresistance ratio deviation &lt;i&gt;β&lt;/i&gt; increases to 30%. The writing error rate can be effectively reduced by increasing &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;b1&lt;/sub&gt;, and increasing &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;b2&lt;/sub&gt; when writing ‘0’ or reducing &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;b2&lt;/sub&gt; when writing ‘1’ in the NV-FA circuit. The output error rate can also be effectively reduced by increasing the driving voltage of logical operation &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;dd&lt;/sub&gt;.

Perpendicular Magnetic Anisotropy and Its Electric Field Manipulation in Magnetic Multilayered Heterostructures

"Understanding of underlying physics related to the Perpendicular Magnetic Anisotropy (PMA) in magnetic heterostructures represents a major issue for its exploit in random-access memory (MRAM) devices. Using ab-initio analysis, we reveal some basic aspects related to the anatomy of PMA and its variation with electric field in various X/Fe/MgO(001) multilayer configurations (X=Cr, Au, V, Ag, Pt, Pd,…) compatible with standard experimental architectures of magnetic tunnel junction devices. Our study quantifies and underlines the significant role of the Rashba interfacial field on PMA. We explain and correlate the sign, the magnitude, and the electric field dependence of the PMA, the Rashba coefficient R and the Dzyaloshinskii–Moriya (DMI) asymmetric exchange interaction parameter. Moreover, when varying the Fe thickness in X/Fe/MgO(001) systems, we observe oscillations of PMA with the number of Fe monolayers, explained within the framework of quantum wells of the 1 Bloch symmetry electrons in Fe. Further atomistic micromagnetic simulations including different Fe layer thicknesses and the corresponding PMA predict macroscopic magnetization characteristics in realistic experimental systems. Keywords: perpendicular magnetic anisotropy, electric field control of PMA, magnetic tunnel junctions, magnetic multilayer heterostructures, atomistic magnetic simulations. "