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The tuning of sensitivity and dynamic range in linear magnetic sensors is required in various applications. We demonstrate the control and design of the sensitivity in magnetic tunnel junction (MTJ) sensors with a vortex-type sensing layer. In this work, we develop sensor MTJs with NiFe sensing layers having a vortex magnetic configuration. We demonstrate that by varying the pinned layer size, the sensitivity to magnetic field is tuned linearly. We obtain a high magnetoresistance ratio of 140 %, and we demonstrate a controllable sensitivity from 0.85 to 4.43 %/Oe, while keeping the vortex layer fixed in size. We compare our experimental results with micromagnetic simulations. We find that the linear displacement of vortex core by an applied field makes the design of vortex sensors simple. The control of the pinned layer geometry is an effective method to increase the sensitivity, without affecting the vortex state of the sensing layer. Furthermore, we propose that the location of the pinned layer can be used to realize more sensing functionalities from a single sensor., accepted manuscript

${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ is the archetypal magnetoelectric (ME) material, which has a linear coupling between electric and magnetic polarizations. Quadratic ME effects are forbidden for the magnetic point group of ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$, due to space-time inversion symmetry. In ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ films grown by sputtering, we find a signature of a quadratic ME effect that is not found in bulk single crystals. We use Raman spectroscopy and magnetization measurements to deduce the removal of space-time symmetry and corroborate the emergence of the quadratic ME effect. We propose that metastable site-selective trace dopants remove the space, time, and space-time inversion symmetries from the original magnetic point group of bulk ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$. We include the quadratic ME effect in a model describing the switching process during ME field cooling and estimate the effective quadratic susceptibility value. The quadratic magnetoelectric effect in a uniaxial antiferromagnet is promising for multifunctional antiferromagnetic and magnetoelectric devices that can incorporate optical, strain-induced, and multiferroic effects.

Continuous low-rate monitoring is an important IoT application, which requires high-fidelity in observing signals with low frequency. However, most sensors exhibit noise that is inversely-proportional to spectral frequency (1/f noise). Because both the relevant signal and noise share the same spectral properties, standard linear filtering techniques cannot be used. We are looking into a special application for remote healthcare of the magnetic field sensing of cardiac activity, magnetocardiography (MCG). For such an application, we need to develop a noise separation method, that is also resource-efficient. Previously, we demonstrated AI-based removal of 1/f noise in MCG by a convolutional neural network coupled with gated recurrent units. However, it needs a large amount of data for training, requiring significant training time and computational power. In this work, we employ reservoir computing (RC) for noise-removal, while being conservative in computing resources.

Bilayer films consisting of a 15 nm thick Pt x Mn 100-x (x = 48 or 15) layer and a 2 nm thick Co y Fe 100-y (0 ≤ y ≤ 90) layer were fabricated by ultrahigh-vacuum magnetron sputtering. The Pt 48 Mn 52 and Pt 15 Mn 85 films consisted of face-centered tetragonal (FCT) and face-centered cubic (FCC) structures, respectively. The effect of composition of CoFe films on the unidirectional anisotropy constant (Jk) in the Pt x Mn 100-x /Co y Fe 100- y bilayer films and the optimum conditions for producing large Jk were determined. The FCT and FCC PtMn films annealed at 370 °C for 6 h both exhibited maximum J k when the film composition was Co 70 Fe 30 . Blocking temperatures of the FCT and FCC PtMn films were 410 °C and 160 °C, respectively. All the bilayer films possess flat surfaces. These results indicate that the obtained Pt-Mn films-with low roughness, high exchange bias, and high blocking temperature-will be practical candidates as the antiferromagnetic layer in spintronic devices.

Quantum-well (QW) devices have been extensively investigated in semiconductor structures. More recently, spin-polarized QWs were integrated into magnetic tunnel junctions (MTJs). In this Letter, we demonstrate the spin-based control of the quantized states in iron $3d$-band QWs, as observed in experiments and theoretical calculations. We find that the magnetization rotation in the Fe QWs significantly shifts the QW quantization levels, which modulate the resonant-tunneling current in MTJs, resulting in a tunneling anisotropic magnetoresistance (TAMR) effect of QWs. This QW-TAMR effect is sizable compared with other types of TAMR effect, and it is present above room temperature. In a QW MTJ of $\mathrm{Cr}/\mathrm{Fe}/{\mathrm{MgAl}}_{2}{\mathrm{O}}_{4}/\mathrm{top}$ electrode, where the QW is formed by a mismatch between Cr and Fe in the $d$ band with ${\mathrm{\ensuremath{\Delta}}}_{1}$ symmetry, a QW-TAMR ratio of up to 5.4% was observed at 5 K, which persisted to 1.2% even at 380 K. The magnetic control of QW transport can open new applications for spin-coupled optoelectronic devices, ultrathin sensors, and memory.

An inserted metal (IM) layer (such as Pt, Ru, or Cr) is typically fabricated between Cr2O3 and the ferromagnet in magnetoelectric switched antiferromagnet/ferromagnet exchange-biased thin film systems. The IM layer is used as a “spacer layer” to prevent oxidization of Co and enhance the blocking temperature. In this work, we found that the magnetic properties of these thin film systems vary depending on the type of IM, and they could be reproduced by bilayers or multilayers of Co and IM thin films. We also found that the IM layer was spin-polarized by the Co ferromagnetic layer based on X-ray magnetic circular dichroism data. These results suggest that the IM does not work separately as a “spacer layer”, but rather it is an integral component of Co-based stacked ferromagnetic films in magnetoelectric switched Cr2O3/ferromagnet exchange-biased systems. Furthermore, we found that some stacked ferromagnetic films easily exhibit a low unidirectional anisotropy energy (Jk), which may be a good way to decrease the magnetoelectric switching energy of antiferromagnets for practical device applications.

The present investigation deals with the effect of thickness and a platinum (Pt) buffer layer on the dynamic magnetic properties of polycrystalline yttrium iron garnet (YIG) films fabricated after post-annealing to recrystallize from the amorphous state. The dynamic magnetic properties of films without a buffer layer deteriorate as the thickness decreases as indicated by the increased line-widths in the ferromagnetic resonance spectra. On the other hand, a strong rejuvenation in the static and dynamic magnetic properties of the films is observed when a Pt buffer layer is used. The Pt buffer layer decreases the Gilbert damping parameter from $11.4 \times 10^{-4}$ and $3.5 \times 10^{-4}$ for a 100 nm-thick YIG film. These observations mainly originate from controlling the microstructure or the surface morphology of the films.

In this work, we investigated the temperature dependence of interface exchange coupling in an Ir-doped Fe2O3/Co system with variations in the Ir–Fe2O3 thickness. Low-temperature perpendicular exchange bias was observed in the samples with an Ir–Fe2O3 thickness of 5 nm or less, when it cooled from 360 K in an external magnetic field of 1 T perpendicular to the sample surface. For 5 nm-thick Ir–Fe2O3, a maximum exchange bias value of 1200 Oe was obtained at 200 K. This is the first report on perpendicular exchange bias of an Fe2O3 thin film coupled with a ferromagnet. Enhancements to the Morin temperature and the magnetic anisotropy of Fe2O3 caused by lattice strain, Ir doping, and the finite-size scaling effect, as well as the high quality (good crystal orientation, small roughness, etc.) of the Fe2O3 film fabricated by our process, are considered to be mostly responsible for the perpendicular exchange bias obtained.

We studied the effect of second-order magnetic anisotropy on the linear conductance output of magnetic tunnel junctions (MTJs) for magnetic-field-sensor applications. Experimentally, CoFeB/MgO/CoFeB-based MTJs were fabricated, and the nonlinearity, NL was evaluated for different thicknesses, t of the CoFeB free layer from the conductance. As increasing t from 1.5 to 2.0 nm, maximum NL, NLmax was found to decrease from 1.86 to 0.17% within the dynamic range, Hd = 1.0 kOe. For understanding the origin of such NL behavior, a theoretical model based on the Slonczewski model was constructed, wherein the NL was demonstrated to be dependent on both the normalized second-order magnetic anisotropy field of Hk2/|Hkeff| and the normalized dynamic range of Hd/|Hkeff|. Here, Hkeff, Hk2, are the effective and second-order magnetic anisotropy field of the free layer in MTJ. Remarkably, experimental NLmax plotted as a function of Hk2/|Hkeff| and Hd/|Hkeff|, which were measured from FMR technique coincided with the predictions of our model. Based on these experiment and calculation, we conclude that Hk2 is the origin of NL and strongly influences its magnitude. This finding gives us a guideline for understanding NL and pioneers a new prospective for linear-output MTJ sensors to control sensing properties by Hk2.

The electric control of magnetic anisotropy has important applications for nonvolatile memory and information processing. By first-principles calculations, we show a large nonvolatile control of magnetic anisotropy in the ferromagnetic/ferroelectric CoPt/ZnO interface. Using the switched electric polarization of ZnO, the density-of-states and magnetic anisotropy at the CoPt surface show a large change. Due to a strong Co/Pt orbitals hybridization and a large spin-orbit coupling, a large control of magnetic anisotropy was found. We experimentally measured the change of effective anisotropy by tunneling resistance measurements in CoPt/Mg-doped ZnO/Co junctions. Additionally, we corroborate the origin of the control of magnetic anisotropy by observations on tunneling anisotropic magnetoresistance.

As we are about to embark upon the highly hyped "Society 5.0", powered by the Internet of Things (IoT), traditional ways to monitor human heart signals for tracking cardio-vascular conditions are challenging, particularly in remote healthcare settings. On the merits of low power consumption, portability, and non-intrusiveness, there are no suitable IoT solutions that can provide information comparable to the conventional Electrocardiography (ECG). In this paper, we propose an IoT device utilizing a spintronic ultra-sensitive sensor that measures the magnetic fields produced by cardio-vascular electrical activity, i.e. Magentocardiography (MCG). After that, we treat the low-frequency noise generated by the sensors, which is also a challenge for most other sensors dealing with low-frequency bio-magnetic signals. Instead of relying on generic signal processing techniques such as averaging or filtering, we employ deep-learning training on bio-magnetic signals. Using an existing dataset of ECG records, MCG labels are synthetically constructed. A unique deep learning structure composed of combined Convolutional Neural Network (CNN) with Gated Recurrent Unit (GRU) is trained using the labeled data moving through a striding window, which is able to smartly capture and eliminate the noise features. Simulation results are reported to evaluate the effectiveness of the proposed method that demonstrates encouraging performance., Comment: Presented at IEEE International Conference on Communications 2020

Magnetic sensors to detect magnetic nanoparticles (MNPs) towards biomedical applications require very high sensitivity at low magnetic fields. Here we report a magnetic sensor consisting of a magnetic tunnel junction (MTJ) with a synthetic antiferromagnetic free layer. This sensor exhibits a low magnetic anisotropy and sensitivities of over 18%/Oe at low fields in the range of 0 to 3 Oe. We employ superparamagnetic MNPs with a large diameter of 200 nm. The sensor’s transfer curves show the magnetoresistance (MR) variations as a function of MNP concentration. We demonstrate the detection capability of MNP amounts of below 500 ng and low MNP concentrations of 0.01, 0.1, and 1 mg/ml in solvents. This result suggests that the combination of high-sensitivity TMR sensors and large MNPs has a substantial potential for biomarker detection applications.

In Cr2O3 thin films doped with Al or Ir, we have discovered a parasitic magnetization, accompanied by the antiferromagnetic order, with tunable direction and magnitude. In this study, by utilizing the parasitic magnetization, the antiferromagnetic anisotropy KAF of the doped Cr2O3 thin films was evaluated. A much greater improvement of KAF was obtained for Al-doped Cr2O3 films than that of bulk. The maximum KAF in this study was ∼9 × 104 J/m3, obtained for the Al 3.7%-doped Cr2O3 film sample. The enhancement of the magnetic dipole anisotropy KMD due to the site-selective substitution is speculated for the dominant origin of the enhancement. Furthermore, based on the obtained KAF, the influence of the parasitic magnetization on the exchange bias blocking temperature TB of the doped-Cr2O3/Co exchange coupled system was discussed. TB greatly increases when the parasitic magnetization is coupled antiparallel to ferromagnetic moment, such as Al-doped Cr2O3/Co systems.

The control of magnetic domain formation and fluctuations in the sensing layer is important to progress for low noise in magnetic tunnel junction sensors. We studied the effect of exchange bias on the domain structure in micro-patterned Permalloy (Py: Ni80Fe20) sensing layer. We deposited single Py films, and Pt48Mn52/Py films, where the latter showed exchange bias. By controlling the thickness of Py, Pt48Mn52 (15nm)/Py (t=235 nm) showed a small coercivity and exchange bias of 7 Oe. After micro-fabrication into circular pillars 80 µm in diameter, we measured the domain structure by Magneto Optical Kerr Effect (MOKE) microscopy. MOKE images showed that single Py pillars have a simple closure domain, where the domain wall at the center moved with the applied field. The exchange-biased Py pillars exhibited a more complicated structure, but with fixed domains at the center region due to the exchange bias overcoming the magnetostatic energy. The uniform rotation of magnetization at the center of the sample is promising for decreasing the domain hopping magnetic noise.

The CoFeB thickness, t dependence of the effective first- and second-order magnetic anisotropy, K1eff and K2, for MgO/(Co1-xFex)80B20/Ta films (x=0.3-1.0) is investigated. As Co40Fe40B20 thickness decreases, K1eff increases and shows a perpendicular magnetic anisotropy for t=1.2 nm. On the other hand, in-plane magnetic anisotropy is observed for t≥1.4 nm. Also, a 1.3-nm-thick CoFeB sample demonstrates an easy-cone behavior, which suggests that the magnitude of K1eff and K2 becomes comparable. By plotting the product of K2 and t-td as a function of t-td, where td is a magnetic dead layer thickness, linear dependences with negative y-axis intercepts are displayed for all ranges of x. The extracted interfacial K2, Ki(2) are varied depending on the compositions in the range of-0.024 to −0.042 erg/cm2 for x=100% and 30, 50%, respectively. A magnetic phase diagram summarizing the results of K1-2πMs2 and K2 suggests that the ratio of K2 against K1-2πMs2 is varied depending on the compositions. These results give us a guideline to achieve the desired magnetic properties of CoFeB for spintronic applications.

Recently, yttrium iron garnet (YIG, Y3Fe5O12) has been proved to be an efficient material for magnonics and spintronics application after discovery of spin pumping [1], spin seebeck effect [2] and spin hall magnetoresistance [3] phenomena.

The scaling of antiferromagnetic ordering temperature of corundum-type chromia films has been investigated. N\'eel temperature ${T}_{N}$ was determined from the effect of perpendicular exchange bias on the magnetization of a weakly-coupled adjacent ferromagnet. For a thick-film case, the validity of detection is confirmed by a susceptibility measurement. Detection of ${T}_{N}$ was possible down to 1-nm-thin chromia films. The scaling of ordering temperature with thickness was studied using different buffering materials and compared with Monte-Carlo simulations. The spin-correlation length and the corresponding critical exponent were estimated, and they were consistent between experimental and simulation results. The spin-correlation length is an order of magnitude less than cubic antiferromagnets. We propose that the difference is from the change of number of exchange-coupling links in the two crystal systems.

The quantum well (QW) realizes new functionalities due to the discrete electronic energy levels formed in the well‐shaped potential. Magnetic tunnel junctions (MTJs) combined with a quasi‐QW structure of Cr/ultrathin‐Fe/MgAl2O4(001)/Fe, in which the Cr quasi‐barrier layer confines Δ 1 up‐spin electrons to the Fe well, are prepared with perfectly lattice‐matched interfaces and atomic layer number control. Resonant peaks are clearly observed in the differential conductance of the MTJs due to the formation of QWs. Furthermore, enhanced tunnel magnetoresistance (TMR) peaks at the resonant bias voltages are realized for the MTJs at room temperature, i.e., it is observed that TMR ratios at specific and even high bias‐voltages (V bias) are larger than zero‐bias TMR ratios for the MTJs with odd Fe atomic layers, in contrast to the earlier experimental studies. In addition, a new finding in this study is unique sign changes in the temperature coefficient of resistance (TCR) depending on the Fe thickness and V bias, which is interpreted as a signature of the QW formation of Δ1 symmetry electronic states. The present study suggests that the spin‐dependent resonant tunneling via the QWs formed in Cr/ultrathin‐Fe/MgAl2O4/Fe structures should open a new pathway to achieve a large TMR at practically high V bias., Inside Cr/ultrathin‐Fe/MgAl2O4/Fe‐based magnetic tunnel junctions, quantum well (QW) states are established within a precisely thickness‐controlled ultrathin Fe layer. Via the QW states, the tunnel magnetoresistance (TMR) is strongly modulated at room temperature. For odd Fe atomic layer cases, the resonance appears at a high bias voltage, where the TMR is even higher than the value at zero bias.

A combined analysis of Ir-doped α-Fe2O3 (001) films, which show a drastic enhancement in the Morin transition temperature as a result of Ir doping, was performed by employing X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and Mossbauer spectroscopy analyses at room temperature. The Mossbauer spectra reveal that the valency of Fe remains 3+ after Ir doping. The XANES spectra indicate that the valency of the Ir ion in Ir-doped α-Fe2O3 varies from 3+ to 4+. The EXAFS analysis results clarified that the Ir ions occupy the Fe-sites of α-Fe2O3. These findings help elucidate the mechanism for controlling the Morin transition temperature in α-Fe2O3 films toward antiferromagnetic spintronic applications.

The electric manipulation of antiferromagnets has become an area of great interest recently for zero-stray-field spintronic devices, and for their rich spin dynamics. Generally, the application of antiferromagnetic media for information memories and storage requires a heterostructure with a ferromagnetic layer for readout through the exchange-bias field. In magnetoelectric and multiferroic antiferromagnets, the exchange coupling exerts an additional impediment (energy barrier) to magnetization reversal by the applied magnetoelectric energy. We proposed and verified a method to overcome this barrier. We controlled the energy required for switching the magnetic domains in magnetoelectric ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ films by compensating the exchange-coupling energy from the ferromagnetic layer with the Zeeman energy of a small volumetric spontaneous magnetization found for the sputtered ${\mathrm{Cr}}_{2}{\mathrm{O}}_{3}$ films. Based on a simplified phenomenological model of the field-cooling process, the magnetic and electric fields required for switching could be tuned. As an example, the switching of antiferromagnetic domains around a zero-threshold electric field was demonstrated at a magnetic field of 2.6 kOe.

Spin-torque oscillators are strong candidates as nano-scale microwave generators and detectors. However, because of large amplitude-phase coupling (non-linearity), phase noise is enhanced over other linear auto-oscillators. One way to reduce nonlinearity is to use ferromagnetic layers as a resonator and excite them at localized spots, making a resonator-excitor pair. We investigated the excitation of oscillations in dipole-coupled ferromagnetic layers, driven by localized current at ferromagnetic nano-contacts. Oscillations possessed properties of optical-mode spin-waves and at low field ($\approx$200 Oe) had high frequency (15 GHz), a moderate precession amplitude (2--3$^\circ$), and a narrow spectral linewidth ($

We investigated the effect of Al doping on the perpendicular exchange bias in Cr2O3/Co thin film systems. By Al doping, a large unidirectional anisotropy energy (J K ~ 0.74 erg/cm2) and a high blocking temperature (T B) were obtained simultaneously. The variations in J K and T B induced by Al doping were discussed on the basis of Mauri's model and explained from an increase in magnetic anisotropy and a decrease in the exchange stiffness constant of Cr2O3. Our first-principles calculations suggest a factor to improve the magnetic anisotropy of Cr2O3 markedly, which is different from the previously established lattice strain effect.

We investigated perpendicular exchange bias switching by a magnetoelectric field cooling process in a Pt-spacer-inserted Cr2O3/Co exchange-coupled system exhibiting small Cr2O3 magnetization. Although higher magnetoelectric switching energies with decreasing Cr2O3 thickness due to the exchange bias were reported in Cr2O3/Co all-thin-film systems, in this study, we demonstrated low-energy switching in a magnetoelectric field cool process regardless of the exchange-bias magnitude; we balanced the exchange-bias energy with the Zeeman energy associated with finite magnetization in Cr2O3. We proposed a guideline for realizing low-energy switching in thin Cr2O3 samples.

A pure-phase, unstrained and epitaxial α-Fe2O3 film of thickness 250 nm has been fabricated by reactive rf sputtering over c-Al2O3 substrate with nominal average surface roughness of 0.71 nm. Field induced spin-reorientation temperature (TSR) and temperature dependent spin-reorientation field (HSR) have been investigated. A linear relationship in the result has been found with ∂TSR/∂HSR equal to −0.92 ± 0.05 K kOe−1 and −0.89 ± 0.175 K kOe−1 by both methods, respectively. The field induced entropy change is argued to be the possible cause for the shift in the spin-reorientation temperature with applied field. The entropy change associated with the first-order phase transition is calculated on the basis of Clausius–Clapeyron equation and found to be 0.029 J kg−1 K−1.

We investigated the switching of perpendicular exchange bias (PEB) from a negative to a positive value in an exchange-coupled Cr2O3/Pt/Co heterostructure. With varying the Pt spacer layer thickness or the measurement temperature, two types of intermediate states were found during the switching process: a double hysteresis loop indicating a local PEB and a single hysteresis loop indicating an averaged PEB. We propose a way to control the lateral ferromagnetic domain, which is associated with the type of the intermediate state, through the control of the exchange coupling magnitude.

Chromium(III) oxide is a classical collinear antiferromagnet with a linear magnetoelectric effect. We are presenting the measurements of the magnetoelectric susceptibility $\alpha$ of a sputter-deposited 500-nm film and a bulk single-crystal of Cr$_\mathrm{2}$O$_\mathrm{3}$. We investigated the magnetic phase-transition and the critical exponent $\beta$ of the sublattice magnetization near N\'eel temperature. For the films, an exponent of 0.49(1) was found below 293 K, and changed to 1.06(4) near the N\'eel temperature of 298 K. For the single-crystal, the exponent was constant at 0.324(4). We investigated the reversal probability of antiferromagnetic domains during magnetoelectric field cooling. For the sputtered films, reversal probability was zero above 298 K and stabilized only below 293 K. We attribute this behavior to formation of grains during film growth, which gives different intergrain and intragrain exchange-coupling energies. For the single-crystal, reversal probability was stabilized immediately at the N\'eel temperature of 307.6 K.

The electric control of surface magnetism is important for spintronic applications. Due to the screening of electric field by conduction electrons in metals, an electric field can be applied only at a surface layer. However, the electric field can be applied on metallic contacts smaller than the electron's mean free path. We report on the electric modulation of the phase-transition temperature of CoO that is present at Co/Pt nano-contacts through a thin AlO x barrier. We found a 50-K/V change that can be attributed to the injection of electrons through nano-contacts.

We investigated the tunneling electroresistance (TER) in metal/wurtzite-MgZnO/metal junctions for applications in nonvolatile random-access memories. A resistive switching was detected utilizing an electric-field cooling at ±1 V and exhibited a TER ratio of 360%–490% at 2 K. The extracted change in the average barrier height between the two resistance states gave an estimation of the MgZnO electric polarization at 2.5 μC/cm2 for the low-temperature limit. In addition, the temperature-dependent TER ratio and the shift of the localized states energies at the barrier interface supported the ferroelectric behavior of the MgZnO tunnel-barrier. From the first-principles calculations, we found a similar effect of the barrier height change coming from the reversal of ZnO electric polarization. The possibility of using metal electrodes and lower growth temperatures, in addition to the ferroelectric property, make the ZnO-based memory devices suitable for CMOS integration.

An epitaxial wurtzite (WZ) Mg0.23Zn0.77O barrier based magnetic tunnel junction (MTJ), with electrode-barrier structure of Co0.30Pt0.70 (111)/Mg0.23Zn0.77O (0001)/Co (0001), was fabricated. The good crystallinity and tunneling properties were experimentally confirmed. Electrical and magnetic investigations demonstrated its high resistance-area product of 1.05 MΩ μm2, a maximum tunneling magneto-resistance (TMR) of 35.5%, and the existence of localized states within the tunneling barrier producing TMR rapid decrease and oscillation when increasing the applied bias voltage. The TMR value almost vanished at 200 K, which was attributed to the induced moment and strong spin-orbit coupling in Pt atoms at the Co0.30Pt0.70/Mg0.23Zn0.77O interface. Owing to the ferroelectric behavior in WZ-MgZnO materials, the fabrication of WZ-MgZnO barrier based MTJs deposited on a metallic ferromagnetic electrode will open routes for electrically controllable non-volatile devices that are compatible with CMOS technology.

We report on the observation of anisotropic magnetoresistance (AMR) in vertical asymmetric nano-contacts (NCs) made through AlO$_x$ nano-oxide layer (NOL) formed by ion-assisted oxidation method in the film stack of Co/AlO$_x$-NOL/Pt. Analysis of NC formation was based on \emph{in situ} conductive atomic force microscopy and transmission electron microscopy. Depending on the purity of NCs from Al contamination, we observed up to 29% AMR ratio at room temperature.