PbTiO3 Heterostructure Research Articles

Mapping the complex evolution of ferroelastic/ferroelectric domain patterns in epitaxially strained PbTiO3 heterostructures

We study the complex ferroelastic/ferroelectric domain structure in the prototypical ferroelectric PbTiO3 epitaxially strained on (110)o-oriented DyScO3 substrates, using a combination of atomic force microscopy, laboratory and synchrotron x-ray diffraction, and high resolution scanning transmission electron microscopy. We observe that the anisotropic strain imposed by the orthorhombic substrate creates a large asymmetry in the domain configuration, with domain walls macroscopically aligned along one of the two in-plane directions. We show that the periodicity as a function of film thickness deviates from the Kittel law. As the ferroelectric film thickness increases, we find that the domain configuration evolves from flux-closure to a/c-phase, with a larger scale arrangement of domains into superdomains.

Interfacial charge and strain effects on lanthanum doped barium stannate thin film under ferroelectric gating

Interfacial charge and strain are two coupling effects in semiconductor/ferroelectric epitaxial heterostructures, which are pivotal for use in tailoring functionalities in devices. In this work, La0.04Ba0.96SnO3/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 heterostructures with varying film thicknesses were prepared in order to understand both charge and strain's contributions to the electric-field induced resistance change. The relative resistance change to the lattice strain remains almost unchanged in those thicker films, while increases a little bit in those thinner films. This slight increase is related to the substrate constraint near the interface and follows Freund's strain relaxation model during the dynamic strain induced by the piezoelectric switch. A depletion layer model was also established to simulate the electroresistance variation from the interfacial charge effect. The depletion layer involves an equilibrium between capture and release of electrons by the acceptor-like defects near the interface region. The resistance change vs electric field evolves from a butterfly-like shape to a square-like when decreasing the film thickness, due to the joint effect of strain and interfacial polarization screening charge. This study provides an insight into understanding heteroepitaxial coupling and exploring their potential applications in oxide electronic devices.

Electric-field control of non-volatile 180° switching of the unidirectional anisotropy field in a multiferroic heterostructure.

We investigate the room-temperature, electric-field-mediated, non-volatile 180° switching of the unidirectional anisotropy field in an IrMn/CoFeB/Ta/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure. The variation in exchange bias under different electric fields appears clearly in the magnetic hysteresis loops. The remnant magnetization as a function of electric field, as determined by static magnetic measurements, exhibits a non-volatile behavior, which is consistent with the results of the ferromagnetic resonance field as a function of electric field. Moreover, the measured ferromagnetic resonance shows that the uniaxial magnetic anisotropy field is non-volatile and the unidirectional anisotropy field undergoes 180° switching that can be acquired and separated distinctly. This result is attributed to the piezo-strain effect. The electric-field-mediated non-volatile 180° switching of the unidirectional anisotropy field paves the way for sensors and other spintronic devices.

Piezostrain tuning exchange bias mediated by electric field in composite heterostructure

The change of unidirectional anisotropy and uniaxial anisotropy field turned by piezostrain in an IrMn/Co/Ta/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure with an exchange bias was investigated by ferromagnetic resonance at room temperature. The curve of the magnetic resonance field versus the electric fields showed an asymmetric butterfly-like behavior, which was consistent with the result of strain versus electric field curves. This butterfly-like behavior can be attributed to the piezostrain effect. Specifically, the non-volatile uniaxial anisotropy field and unidirectional anisotropy field behavior under different electric fields induced by piezostrain effect were obtained. Our result is crucial for further application of future multiferroic devices.

Large non-volatile tuning of magnetism mediated by electric field in Fe–Al/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure

Electric-field control of magnetism is now an attractive trend to approach a new kind of fast, low-power-cost memory device. In this work, we report a strong non-volatile electric control of magnetism in an Fe–Al/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure. In this system, a 90° rotation of the in-plane uniaxial magnetic anisotropy is exhibited during the increase of the external electric field, which means the easy axis turns into a hard axis and the hard axis turns into an easy one. Additionally, a non-volatile switch of the remanence is observed after a sweeping of the electric field from 0 kV cm−1 to ± 10 kV cm−1, then back to 0 kV cm−1. More interestingly, a 20% non-volatile magnetic state tuning driven by individual pulse electric fields is shown in contrast to large tuning up to 120% caused by pulse electric fields with small assistant pulse magnetic fields, which means a 180° reverse of the magnetization. These remarkable behaviors demonstrated in this heterostructure reveal a promising potential application in magnetic memory devices mediated by electric fields.

Modulation of persistent magnetoresistance by piezo-strain effect in manganite-based heterostructures

Persistent magnetoresistance effects in the phase-separated Pr0.65(Ca0.25Sr0.75)0.35MnO3/SrTiO3 and Pr0.65(Ca0.25Sr0.75)0.35MnO3/0.7PbMg1/3Nb2/3O3–0.3PbTiO3 heterostructures under a low magnetic field are investigated. It is observed that the persistent magnetoresistance effects decrease with increasing temperatures and the values for the heterostructures on 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 and SrTiO3 substrates are about 86.6% and 33.2% at 40 K, respectively. More interestingly, the applied electric field on the 0.7PbMg1/3Nb2/3O3–0.3PbTiO3 substrate can suppress the persistent magnetoresistance effect, indicating that different energy landscapes can be dramatically modulated by the piezo-strain. These results are discussed in terms of the strain-induced competition in the ferromagnetic state and the charge-ordering phase by the energy scenario, which provide a promising approach for designing devices of electric-magnetic memories in all-oxide heterostructures.

Erratum: “Enhancing polarization by electrode-controlled strain relaxation in PbTiO3 heterostructures” [APL Mater. 4, 016104 (2016)

Erratum: “Enhancing polarization by electrode-controlled strain relaxation in PbTiO3 heterostructures” [APL Mater. 4, 016104 (2016)

Electric field tuning resistance switching behavior of SrRuO3/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructures at various temperatures

The resistance switching behavior induced by in-plane read current in SrRuO3/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructures is investigated at different temperatures. With decreasing in-plane read current from 10 mA to 0.01 mA, the symmetrical butterfly-like shape of resistance is gradually converted to an antisymmetrical shape at different temperatures, which is resulted from the enhancement of polarization current effect. Specifically, non-volatile resistance behaviors induced by asymmetric bipolar sweeping of electric field and pulsed electric field are achieved at different temperatures. Our results suggests resistance switching behavior dependence of in-plane read current, which is crucial for further application of complex oxide magnetoelectric and spintronic devices.

Electric-field modulation of photoinduced effect in phase-separated Pr0.65 (Ca0.75Sr0.25)0.35MnO3/PMN-PT heterostructure

In this letter, we report the photoinduced effect modulated by different electric fields in the Pr0.65 (Ca0.75Sr0.25)0.35MnO3/0.7PbMg1/3Nb2/3O3-0.3PbTiO3 heterostructure. The film exhibits a decrease in the resistance up to five orders of magnitude by enhancing applied electric fields, combined with an electric-field-induced insulator-to-metal transition. More interestingly, a reversible bistability arises in the photoinduced change in resistance at T < 80 K as the voltages are increased. The results can be attributed to the phase separation in manganites, which provides a prototype of photoelectric conversion for electric-field modulation of all-oxide heterostructures.

The Electric-Field Controllable Non-Volatile 35° Rotation of Magnetic Easy Axis in Magnetoelectric CoFeB/(001)-Cut Pb(Mg1/3Nb2/3)O3-25%PbTiO3 Heterostructure**Supported by the National Natural Science Foundation of China under Grant Nos 11374010 and 11434009, and the Fundamental Research Funds for the Central Universities.

Using in situ electric-field-modulated anisotropic magnetoresistance measurement, a large reversible and nonvolatile in-plane rotation of magnetic easy axis of ∼35° between the positive and negative electrical poling states is demonstrated in Co40Fe40B20/(001)-cut Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 (PMN-PT). The specific magnetoelectric coupling mechanism therein is experimentally verified to be related to the synchronous in-plane strain rotation induced by 109° ferroelastic domain switching in the (001)-cut PMN-PT substrate.

Dynamic strain enhanced abnormal percolative transport and colossal electroresistance in (011)-oriented La0.325Pr0.3Ca0.375MnO3/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 heterostructure

Abnormal percolative transport properties have been studied in (011)-oriented La0.325Pr0.3Ca0.375MnO3 (LPCMO)/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (PMN-PT) heterostructure. By introducing a dynamic electric field-induced in-plane anisotropic strain-field in phase separated LPCMO film, we observed a significant promotion of the thermal hysteresis (∼68 K) and a positive colossal electroresistance (∼8450%). Such abnormal hysteresis is believed to be associated with anisotropic strain induced strong pinning effect in the material. This work unambiguously evidenced the importance of the anisotropic strain on the abnormal transport and meanwhile provides alternative opportunity for well understanding the percolation mechanism in inhomogeneous systems.

Electric-Field-Control of Non-Volatile Magnetization Switching in Multiferroic CoFeB/(011)-PMN-PT Heterostructures

The giant converse magnetoelectric coupling (GME) was observed in the multiferroic Co40Fe40B20/(011)-0.7Pb (Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures at room temperature in this investigation. A tunability of magnetization by electric field along the [100] direction was up to-66.7% at-10 Oe bias magnetic fields. Moreover, the non-volatile magnetization switching was found after removal of bipolar electric field. The corresponding remanent magnetic states even without the assistance of bias magnetic fields were stable and could be modulated synchronously by a sequence of pulse electric fields. The 90o rotation of easy axis and non-symmetrical ferroelastic domain switching contributed to the above results. This work is of great significance in designing ultra-low power and non-volatile magnetoelectric memories and other spintronic devices at room temperature.

Enhancing polarization by electrode-controlled strain relaxation in PbTiO3 heterostructures

A large remanent polarization close to theoretical value 80 μC/cm2 of bulk PbTiO3 is achieved in epitaxial heterostructures of (120–600)-nm-thick PbTiO3 films grown by pulsed laser deposition on (001) SrTiO3 substrate using a 100-nm-thick SrRuO3 bottom electrode layer. The heterostructures employing a 50-nm-thick electrode exhibit a significantly smaller polarization of ≤60 μC/cm2. A detailed x-ray diffraction analysis of the crystal structure allows for relating this large polarization to electrode-controlled relaxation of epitaxial strain in PbTiO3. Based on the observed results, we anticipate that the electrode-promoted strain relaxation can be used to enhance polarization in other epitaxial ferroelectric films.

Nonvolatile Modulation Effects of Electric Field on the Magnetic and Electric Properties in La–Ca–MnO3/PMN-PT Heterostructures

We demonstrate that ferroelectric (FE) domain switching induces a nonvolatile tuning of the magnetic and electric properties in La0.6Ca0.4MnO3 (LCMO)/Pb(Mg $_{1/3}$ Nb $_{2/3}$ )O3–PbTiO3 heterostructure. The FE domain switching in the substrate contributes to an in-plane strain that changes the spin exchange coupling in the LCMO layer, and therefore results in a nonvolatile magnetization difference of up to −17.5% at zero external magnetic field, as well as a nonvolatile resistance difference of up to 20.3%. This nonvolatility of the modulation effect on the magnetic and electric properties by an electric field demonstrates great potential for the applications of magnetic and electric devices.

Ferroelectric polarizing-induced non-volatile modulation effect on magnetic properties and its Raman detection in Ni/PMN-PT heterostructure

In situ tuning effect on magnetism is often achieved by electric-field-induced inverse piezoelectric effect in ferromagnetic/piezoelectric structures. Here, we report on a non-volatile tuning of magnetic properties in Ni/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure. Both magnetization difference of up to 60% and coercivity difference of up to 23.2% are obtained by electric-field-induced the change of polar state in the substrate. This modulation effect is observed over a broad range of temperatures. The coincident changes of both magnetic properties and Raman scattering spectra with different polarization times for the heterostructure are detected, which indicates that the non-volatile tuning effect on magnetism is attributed to the change of the magnetic anisotropy result from the ferroelectric polarizing induced-strain.

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.

Anisotropic modulation of magnetic properties and the memory effect in a wide-band (011)-Pr0.7Sr0.3MnO3/PMN-PT heterostructure.

Memory effect of electric-field control on magnetic behavior in magnetoelectric composite heterostructures has been a topic of interest for a long time. Although the piezostrain and its transfer across the interface of ferroelectric/ferromagnetic films are known to be important in realizing magnetoelectric coupling, the underlying mechanism for nonvolatile modulation of magnetic behaviors remains a challenge. Here, we report on the electric-field control of magnetic properties in wide-band (011)-Pr0.7Sr0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructures. By introducing an electric-field-induced in-plane anisotropic strain field during the cooling process from room temperature, we observe an in-plane anisotropic, nonvolatile modulation of magnetic properties in a wide-band Pr0.7Sr0.3MnO3 film at low temperatures. We attribute this anisotropic memory effect to the preferential seeding and growth of ferromagnetic (FM) domains under the anisotropic strain field. In addition, we find that the anisotropic, nonvolatile modulation of magnetic properties gradually diminishes as the temperature approaches FM transition, indicating that the nonvolatile memory effect is temperature dependent. By taking into account the competition between thermal energy and the potential barrier of the metastable magnetic state induced by the anisotropic strain field, this distinct memory effect is well explained, which provides a promising approach for designing novel electric-writing magnetic memories.

Electrical controlled magnetism in FePt film with the coexistence of two phases

A series of FePt films with different magnetic structures are deposited on Pb(Mg1/3Nb2/3)O3–PbTiO3 substrates. By applying an electric field across the piezoelectric single crystal substrate, an magnetoelectric effect is observed in FePt/Pb(Mg1/3Nb2/3)O3–PbTiO3 heterostructure due to the phase transformation between face-centered cubic and face-centered tetragonal phases in the film. Taking advantage of the different coercivity caused by the electric field, the sign of magnetization can be manipulated reversibly at room temperature with the electric field switching on or off. Based on this experimental result, we demonstrate a model for the technology of information storage, in which data can be written electrically without false writing.

Abnormal percolative transport and colossal electroresistance induced by anisotropic strain in (011)-Pr(0.7)(Ca(0.6)Sr(0.4))(0.3)MnO₃/PMN-PT heterostructure.

Abnormal percolative transport in inhomogeneous systems has drawn increasing interests due to its deviation from the conventional percolation picture. However, its nature is still ambiguous partly due to the difficulty in obtaining controllable abnormal percolative transport behaviors. Here, we report the first observation of electric-field-controlled abnormal percolative transport in (011)-Pr0.7(Ca0.6Sr0.4)0.3MnO3/0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 heterostructure. By introducing an electric-field-induced in-plane anisotropic strain-field in a phase separated PCSMO film, we stimulate a significant inverse thermal hysteresis (~ -17.5 K) and positive colossal electroresistance (~11460%), which is found to be crucially orientation-dependent and completely inconsistent with the well accepted conventional percolation picture. Further investigations reveal that such abnormal inverse hysteresis is strongly related to the preferential formation of ferromagnetic metallic domains caused by in-plane anisotropic strain-field. Meanwhile, it is found that the positive colossal electroresistance should be ascribed to the coactions between the anisotropic strain and the polarization effect from the poling of the substrate which leads to orientation and bias-polarity dependencies for the colossal electroresistance. This work unambiguously evidences the indispensable role of the anisotropic strain-field in driving the abnormal percolative transport and provides a new perspective for well understanding the percolation mechanism in inhomogeneous systems.

Coaction and distinguishment of converse piezoelectric and field effects in La0.7Ca0.3MnO3/SrTiO3/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 heterostructures

The volatile and nonvolatile electroresistances related to the converse piezoelectric induced strain and ferroelectric field effects are improved in La0.7Ca0.3MnO3/SrTiO3/0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 heterostructures by inserting a SrTiO3 buffer layer. Due to the coaction of the strain and field effects, the tri-resistance states are observed, and the relative contributions of the two effects on the resistance changes can be quantitatively distinguished by a programmable control of the polarization electric fields in “ON” and “OFF” modes, respectively. Our results indicate that the well-designed heterostructure exhibits potential for application in multifunctional devices.