PT Heterostructures Research Articles

Relaxation behavior of nonvolatile resistance modulation in Zn:SnO2/PMN-PT heterostructures

Relaxation in resistance switching (RS) has severely hindered the stability of memory devices based on oxide-thin-film/ferroelectric heterostructures. In this work, Zn doped SnO2 (ZTO) thin films were deposited on (111)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-0.3PT) substrates to investigate the effect of oxygen vacancies (OVs) on resistance relaxation. The polarization-dependent resistance relaxation is observed in ZTO/PMN-0.3PT heterostructures. The largest relative change in resistance up to 53.6% within 20 min is ascribed to OV diffusion. Local aggregation of positively charged OVs with the application of poling electric field would enhance the Coulomb repulsion and strain in distorted lattice, which could accelerate the OV back-diffusion. Partial positively charged OVs are neutralized in the positive polarization state with the application of +10 kV/cm poling voltage, which weakens the relaxation compared to the negative polarization state. Our work helps to understand the interrelation between OVs and polarization-dependent relaxation of RS properties.

Non-Volatile Regulation of Magnetism via Electric Fields in Polycrystal FeSi/(011) PMN-0.32PT Heterostructures

The choice and configuration of the ferroelectric (FE) substrate and the ferromagnetic (FM) layer in FM/FE heterostructures play an important role in magnetism modification with regard to amplitude and efficiency. In this study, we fabricated FeSi films on low crystalline (011) [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (PMN-0.32PT) using radio frequency magnetron sputtering. In the annealed FeSi/(011) PMN-0.32PT heterostructures, the FeSi film presented with a (011) preferred orientated polycrystalline structure and low magnetocrystalline anisotropy. Both loop-like and butterfly-like magnetism modifications were observed by applying bipolar electric fields, and the weak and abnormal electrically mediated magnetism behaviors were significantly different from the prominent magnetic anisotropy transition in FeSi/(011) PMN-0.3PT. The comparative analyses suggest that the resulting high-quality single-crystalline PMN-xPT and FM films with low coercivity are of great significance for exploring giant, reversible, and non-volatile magnetism regulation.

The influence of interface strain on the magnetization switching process in FeSi/(011)PMN-0.3PT heterostructures

The magnetization switching process of Fe80Si20/(PbMg1/3Nb2/3O3)0.7–(PbTiO3)0.3 (FeSi/PMN-0.3PT) heterostructures under electric-field-induced interface strain effects was investigated using the magneto-optical Kerr effect. In the as-deposited FeSi films with low four-fold magnetic anisotropy, the one-jump and two-jump loops corresponding to the 180° and 90° domain walls were observed and could be regularly tuned by applying saturated and converse electric fields in these crystalline regions. After 300 °C annealing treatment, the heterostructures presented enhanced crystallinity and interface strain effect. By applying an impulse electric field, we achieved a reliable and non-volatile two-jump and three-jump magnetization switching transition. These regulation results further confirm the magnetic anisotropy transition and magnetic energy superposition relationship in FeSi/PMN-0.3PT. The controllable magnetization switching process is significant for understanding the mechanism of magnetic anisotropy competition and for designing the relevant magnetoelectric devices.

Nanostructure‐enhanced magnetoelectric/magnetostrictive properties and reduced losses in self‐assembled epitaxial CuFe2O4–BiFeO3 layers on Pb(Mg1/3Nb2/3)O3–33at%PbTiO3 crystals

AbstractSelf‐assembled two‐phase heterostructures of BiFeO3 and CuFe2O4 (BFO–CuFO) were deposited on (100)‐oriented SrRuO3‐buffered Pb(Mg1/3Nb2/3) O3–33at%PbTiO3 (PMN–PT) by using switching pulsed laser deposition (SPLD), and compared to single layers of CuFO on the same single crystal substrate. The CuFO phase of the self‐assembled layers had notably slimmer M‐H loops than for previously reported vertically integrated CoFe2O4 nanopillar ones, but wider ones than for CuFO/PMN–PT heterostructures. Notable changes in the magnetization of the CuFO nanopillars were found with applied DC electric field (EDC), where Mr/Ms exhibited typical butterfly‐shaped hysteresis with EDC. This was in distinct difference to CuFO/PMN–PT heterostructures which did not exhibit magnetoelectric coupling. The findings demonstrate a trade‐off between magnetoelectric/magnetostrictive properties and loss that can be controlled by nanostructure features.

Nonvolatile Electric‐Field Control of Ferromagnetic Resonance and Spin Pumping in Pt/YIG at Room Temperature

AbstractElectric‐field‐controlled magnetism is of importance in realizing energy efficient, dense and fast information storage and processing. Strain‐mediated converse magneto‐electric (ME) coupling between ferromagnetic and ferroelectric heterostructure shows promise for realizing electric‐controlled magnetism at room temperature and is attracting a number of recent investigations. However, such ME‐effect studies have mainly focus on magnetic metals. In this work, high quality yttrium iron garnet (Y3Fe5O12 (YIG)) films are deposited directly onto (100)‐oriented single‐crystal Pb (Mg1/3Nb2/3)0.7Ti0.3O3 (PMN‐PT) substrates by means of magnetron sputtering. The electric‐field‐induced polarization switching and lattice strain in the PMN‐PT substrate results in two distinct magnetization states in the YIG film that are nonvolatile and electrically reversible. Because of the direct contact between the YIG and the PMN‐PT substrate, an efficient ME coupling and an almost 90° rotation of the easy axis of the YIG film can be realized. Furthermore, the electric‐field‐controlled hysteresis loop‐like ferromagnetic resonance field shifts and spin pumping signals are observed in Pt/YIG/PMN‐PT heterostructures. Thus, the obstacle is overcome via growing high‐quality YIG thin films directly onto PMN‐PT substrates and an efficient manipulation of magnetism and pure spin current transport by electric field is thereby realized. These findings are instructive for future low‐power magnetic insulator‐based spintronic devices.

Dynamic strain control of the metal–insulator transition and non-volatile resistance switching in (0 1 0) VO2/(1 1 1) Pb(Mg1/3Nb2/3)0.7Ti0.3O3 epitaxial heterostructures

High-quality (010) VO2 thin films were epitaxially grown on functional ferroelectric (111)-oriented Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-0.3PT) substrates by reactive magnetron sputtering. The VO2/PMN-0.3PT heterostructures demonstrated metal–insulator transition (MIT) hysteresis with a resistance change of the order of ∼350. Structural characterization of the heterostructures at varying temperatures confirmed that a structural phase transition accompanies the MIT. Moreover, the dynamic strain induced by the converse piezoelectric effect lowers the critical temperature of the MIT from 341.9K at 0kV/cm to 339.1K at 6kV/cm in the VO2/PMN-0.3PT heterostructures. The resistance of the VO2 thin films could be dynamically modulated by electric field-induced strain, with a change ratio of up to 9.8% near the ferroelectric coercive field. Moreover, the heterostructures displayed non-volatile resistance switching, providing the potential to encode binary information at room temperature by proper electric-field cycling. These functional heterostructures based on correlated electron materials may realize dynamic and non-volatile manipulation of the MIT and resistance switching, thus demonstrating great potential for use in energy-efficient and non-volatile oxide electronic devices.

Electrical modulation of magnetism in multiferroic heterostructures at room temperature

Multiferroic heterostructures CoPd/0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (001) (CoPd/PMN–PT) with the thickness of 10 nm were fabricated via magnetron sputtering. The effect of electric field on remanent magnetization, coercivity, and magnetization reversal have been subsequently investigated. A large electric field modulation of magnetism is obtained in strain-mediated CoPd/PMN–PT multiferroic heterostructures. Not only the remanent magnetization but also the magnetic coercivity of CoPd film can be effectively modulated by an electric field. Up to 30.7% of magnetization difference is observed by electric field at the vicinity of the magnetic coercivity. Taking the advantage of the different coercivity controlled by electric field, the magnetization reversal can be assisted by electric field. The magnetization reversal process of the CoPd/PMN–PT heterostructure is dominated by the Kondorsky model. Our results provide great opportunities for electric field-controlled magnetic devices.

The E-Field-Induced Volatile and Nonvolatile Magnetization Switching of CoNi Thin Films in CoNi/PMN-PT Heterostructures

In this paper, we report the giant electric-field (E-field)-induced magnetic anisotropy and magnetization switching in CoNi/Pb(Mg1/3Nb2/3)O3– x PbTiO3(PMN-PT) magnetoelectric heterostructures. For CoNi/PMN-30%PT, the E-field-induced anisotropy shows a volatile behavior; whereas for CoNi/PMN-32%PT, a large and nonvolatile E-field-induced anisotropy field up to 54 kA/m is observed. These behaviors can be understood by measuring the strain versus the E-field curves of two kinds of substrates. On the basis of the E-field-induced nonvolatile magnetic switching, two stable magnetization states defined by applying E-field pulses were demonstrated in CoNi/PMN-32%PT heterostructure, which paves a new way for voltage-write magnetic random memory devices.

Piezostrain-enhanced photovoltaic effects in BiFeO3/La0.7Sr0.3MnO3/PMN–PT heterostructures

BiFeO3 (BFO) is a unique multiferroic material that shows interesting but rather weak photovoltaic effect. Here, we report the integration of Pt/BFO/La0.7Sr0.3MnO3(LSMO) photovoltaic devices on piezoelectric 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (PMN–PT) single-crystal substrates and realized a piezo-photovoltaic effects in the BFO/LSMO/PMN–PT heterostructures through in situ dynamical strain engineering. Upon the application of an electric field of +10kV/cm, an in-plane compressive strain was induced in the PMN–PT via the converse piezoelectric effect, which was effectively transferred to the BFO film through the LSMO, leading to a change in the in-plane strain and bandgap of the BFO film by ~0.12% and ~22meV, respectively. As a result, the power conversion coefficiency (PCE) η was dramatically enhanced by ~218%, corresponding to a gauge factor (Δη/η)/δεxx~1817. The results demonstrate that the dynamic strain engineering of photovoltaic properties using the converse piezoelectric effect is an effective and unique approach for realizing enhanced PCE of ferroelectric thin film-based photovoltaic devices.

Giant electric field tunable magnetic properties in a Co50Fe50/lead magnesium niobate–lead titanate multiferroic heterostructure

Co50Fe50/(0 1 1)-oriented lead magnesium niobate–lead titanate (PMN–PT) multiferroic (MF) heterostructures were fabricated by RF sputtering magnetic films onto PMN–PT substrates. The effect of magnetic layer thickness (30 nm to 100 nm) on the magnetoelectric (ME) coupling in the heterostructures was studied independently, due to the almost constant magnetostriction constant (λ = 40 ± 5 ppm) and similar as-grown magnetic anisotropies for all studied magnetic layer thicknesses. A record high remanence ratio (Mr/Ms) tunability of 95% has been demonstrated in the 65 nm Co50Fe50/PMN–PT heterostructure, corresponding to a large ME constant (α) of 2.5 × 10−6 s m−1, when an external electric field (E-field) of 9 kV cm−1 was applied. Such an MF heterostructure provides considerable opportunities for E-field-controlled multifunctional devices.

Electric-field manipulation of coercivity in FePt/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructures investigated by anomalous Hall effect measurement

The effect of electric field (E-field) on the magnetism of FePt thin films in FePt/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN–PT) heterostructures was investigated by anomalous Hall effect measurement. For FePt films of different thicknesses, the coercivity vs E-field curves show a typical butterfly-like loop behavior. Further results indicate that the coercivity variation is composed of the volatile symmetrical butterfly-like loop and nonvolatile hysteresis loop-like parts, which originate from the volatile and nonvolatile strains induced by the E-field in the PMN–PT(001) substrate, respectively. No significant difference has been observed after inserting a 2 nm W interlayer, suggesting that the charge-mediated coercivity variation is negligible in FePt/PMN–PT heterostructures.

Electric field control of anisotropy and magnetization switching in CoFe and CoNi thin films for magnetoelectric memory devices

We report on the marked change in magnetic anisotropy and magnetization reversal in Co50Fe50/[Pb(Mg1/3Nb2/3O3)]1−x–[PbTiO3]x (PMN–PT) and Co43Ni57/PMN–PT heterostructures under an electric field. For the Co50Fe50/PMN–PT structure, the electric-field-induced magnetic anisotropy field can be as large as 1.2 kOe at 12 kV/cm, corresponding to a magnetoelectric coefficient of 100 Oe cm/kV. In the Co43Ni57/PMN–PT heterostructure, the electric-field-induced anisotropy has a sign opposite to that in Co50Fe50/PMN–PT. As a result, in the [CoNi/Cu/CoFe/Cu]n/PMN–PT heterostructure, the parallel magnetic moment between two magnetic layers in the initial state may become perpendicular under an electric field. On the basis of these discussions, a voltage-write magnetoelectric memory device model is proposed.

Magnetoelectric coupling in multiferroic heterostructure of rf-sputtered Ni–Mn–Ga thin film on PMN–PT

In this paper, we report a preparation of multiferroic heterostructure from thin film of Ni–Mn–Ga (NMG) alloy and lead magnesium niobate–lead titanate (PMN–PT) with effective magnetoelectric (ME) coupling between the film as ferromagnetic material and PMN–PT as piezoelectric material. The heterostructure was prepared by relatively low temperature (400°C) deposition of the film on single crystal of piezoelectric PMN–PT substrate using rf magnetron co-sputtering of Ni50Mn50 and Ni50Ga50 targets. Magnetic measurements by Superconducting Quantum Interference Design (SQIUD) Magnetometer and Vibrating Sample Magnetometer (VSM) on the film revealed that the film is in ferromagnetically ordered martensitic state at room temperature with saturation magnetization of ∼240emu/cm3 and Curie temperature of ∼337K. Piezoresponse force microscopy (PFM) measurement done at room temperature on the substrate showed the presence of expected hysteresis loop confirming the stability of the piezoelectric state of the substrate after deposition. Room temperature ME voltage coefficient (αME) of the heterostructure was measured as a function of applied bias dc magnetic field in Longitudinal–Transverse (L–T) ME coupling mode by lock-in technique. A maximum ME coefficient αME of 3.02mV/cmOe was measured for multiferroic NMG/PMN–PT heterostructure which demonstrates that there is ME coupling between the film as ferromagnetic material and PMN–PT as piezoelectric material.

Giant Electric Field Tuning of Magnetic Properties in Multiferroic Ferrite/Ferroelectric Heterostructures

AbstractMultiferroic heterostructures of Fe3O4/PZT (lead zirconium titanate), Fe3O4/PMN‐PT (lead magnesium niobate‐lead titanate) and Fe3O4/PZN‐PT (lead zinc niobate‐lead titanate) are prepared by spin‐spray depositing Fe3O4 ferrite film on ferroelectric PZT, PMN‐PT and PZN‐PT substrates at a low temperature of 90 °C. Strong magnetoelectric coupling (ME) and giant microwave tunability are demonstrated by a electrostatic field induced magnetic anisotropic field change in these heterostructures. A high electrostatically tunable ferromagnetic resonance (FMR) field shift up to 600 Oe, corresponding to a large microwave ME coefficient of 67 Oe cm kV−1, is observed in Fe3O4/PMN‐PT heterostructures. A record‐high electrostatically tunable FMR field range of 860 Oe with a linewidth of 330–380 Oe is demonstrated in Fe3O4/PZN‐PT heterostructure, corresponding to a ME coefficient of 108 Oe cm kV−1. Static ME interaction is also investigated and a maximum electric field induced squareness ratio change of 40% is observed in Fe3O4/PZN‐PT. In addition, a new concept that the external magnetic orientation and the electric field cooperate to determine microwave magnetic tunability is brought forth to significantly enhance the microwave tunable range up to 1000 Oe. These low temperature synthesized multiferroic heterostructures exhibiting giant electrostatically induced tunable magnetic resonance field at microwave frequencies provide great opportunities for electrostatically tunable microwave multiferroic devices.