Electric field modification of magnetism in Au/La2/3Ba1/3MnO3/Pt device

Pronounced and reversible modulation of the piezoelectric coefficients by a low magnetic field in a magnetoelectric PZT-5%Fe3O4 system

Composite magnetoelectric compounds that combine ferroelectricity/piezoelectricity and ferromagnetism/magnetostriction are investigated intensively for room-temperature applications. Here, we studied bulk composites of a magnetostrictive constituent, ferromagnetic Fe₃O₄ nanoparticles, homogeneously embedded in a ferroelectric/piezoelectric matrix, Pb(Zr_0.52Ti_0.48)O₃ (PZT). Specifically, we focused on PZT-5%Fe₃O₄ samples which are strongly insulating and thus sustain a relatively high out-of-plane external electric field, E_ex,z. The in-plane strain-electric field curve (S(E_ex,z)) was carefully recorded upon successive application and removal of an out-of-plane external magnetic field, H_ex,z. The obtained S(E_ex,z) data exhibited two main features. First, the respective in-plane piezoelectric coefficients, d(E_ex,z) = 200–250 pm/V, show a dramatic decrease, 50–60%, upon application of a relatively low H_ex,z = 1 kOe. Second, the process is completely reversible since the initial value of d(E_ex,z) is recovered upon removal of H_ex,z. Polarization data, P(E_ex,z), evidenced that the Fe₃O₄ nanoparticles introduced static structural disorder that made PZT harder. Taken together, these results prove that the Fe₃O₄ nanoparticles, except for static structural disorder, introduce reconfigurable magnetic disorder that modifies the in-plane S(E_ex,z) curve and the accompanying d(E_ex,z) of PZT when an external magnetic field is applied at will. The room-temperature feasibility of these findings renders the PZT-x%Fe₃O₄ system a solid basis for the development of magnetic-field-controlled PE devices.

Electric field control of resistive switching and magnetization in epitaxial LaBaCo2O5+δ thin films

The low operating temperature and volatile characteristics of the magnetization change are the main obstacles for the practical applications of spintronic and magnetic memories. In this work, both the resistive switching and magnetization switching are realized in Pt/LaBaCo2O5+δ (LBCO)/Nb-doped SrTiO3 (Nb-STO) devices at room temperature through an electric field. Unlike the traditional approach of an external stress inducing a volatile magnetization change, the magnetization in the Pt/LBCO/Nb-STO device is modulated by an electrical field, along with the resistive switching. The resistive and magnetization switching can be attributed to the variation of the depletion layer width at the LBCO/Nb-STO interface via oxygen vacancy migration and the increase/decrease of the Co-O-Co bond length, respectively. The present device with the synchronous manipulation of both resistance and magnetization at room temperature can be applied in nonvolatile resistive memories and novel magnetic multifunctional devices.

Nonvolatile Control of Magnetocaloric Operating Temperature by Low Voltage

The limited operating temperature is the main obstacle for the practical applications of magnetic refrigeration. In this work, the voltage control of magnetocaloric effect (MCE) is investigated in a La_0.7Sr_0.3MnO₃ (LSMO)/CeO₂/Pt device. Different from the conventional method of volatile manipulating MCE by large-voltage-induced strain, nonvolatile manipulation of magnetocaloric operating temperature with good stability is realized in the LSMO film by applying low voltages of less than 2.3 V. The experimental results demonstrate that the magnetic entropy change peak temperature for the LSMO film can be extended from 302 to 312 K by voltage. This nonvolatile effect can be well-understood with the resistive switching mechanism and has potential in promoting microscale refrigeration technology.

Valence Change Bipolar Resistive Switching Accompanied With Magnetization Switching in CoFe2O4 Thin Film

Resistive Switching in oxides has offered new opportunities for developing resistive random access memory (ReRAM) devices. Here we demonstrated bipolar Resistive Switching along with magnetization switching of cobalt ferrite (CFO) thin film using Al/CFO/FTO sandwich structure, which makes it a potential candidate for developing future multifunctional memory devices. The device shows good retention characteristic time (>10⁴ seconds) and endurance performance, a good resistance ratio of high resistance state (HRS) and low resistance state (LRS) ~10³. Nearly constant resistance values in LRS and HRS confirm the stability and non-volatile nature of the device. The device shows different conduction mechanisms in the HRS and LRS i.e. Schottky, Poole Frenkel and Ohmic. Magnetization of the device is also modulated by applied electric field which has been attributed to the oxygen vacancies formed/annihilated during the voltage sweep and indicates the presence of valence change mechanism (VCM) in our device. It is suggested that push/pull of oxygen ions from oxygen diffusion layer during voltage sweep is responsible for forming/rupture of oxygen vacancies conducting channels, leading to switching between LRS and HRS and for switching in magnetization in CFO thin film. Presence of VCM in our device was confirmed by X-ray Photoelectron Spectroscopy at Al/CFO interface.

Transport properties and electroresistance of a manganite based heterostructure: role of the manganite-manganite interface

In this paper, we report the results of the investigations on the transport properties performed across the manganite-manganite interface in the LaMnO3-δ/La0.7Ca0.3MnO3/LaAlO3 (LMO/LCMO/LAO) heterostructure. The bilayered heterostructure was synthesized by a low cost and simple chemical solution deposition (CSD) method by employing the acetate precursor route. The same LMO/LCMO/LAO heterostructure was also grown using the dry metal oxide chemical vapor deposition (CVD) method and the results of transport characterization have been compared on the basis of wet and dry chemical methods used. XRD Φ-scan measurements were carried out to verify the structural quality and crystallographic orientations of LMO and LCMO manganite layers, for both wet and dry chemical method grown heterostructures. For wet and dry chemical methods, the temperature dependent resistance of the LMO/LCMO interface suggests the metallic nature. The asymmetric I-V curves collected at different temperatures show normal diode characteristics which get transformed to backward diode characteristics at high temperatures under high applied voltages at Vtr for both the methods. The values of Vtr are strongly dependent on the chemical method used. I-V data have been fitted using the Simmons model at different temperatures and discussed in terms of the spin-flip scattering mechanism for both wet and dry chemical method grown heterostructures. The electric field dependent electroresistance (ER) behavior of the presently studied LMO/LCMO manganite-manganite interface, grown using wet and dry chemical methods, has been understood on the basis of complex mechanisms including charge injection, formation of the depletion region, the tunneling effect, thermal processes and junction breakdown and their dependence on the applied electric field, field polarity and temperature studied.

Switching mechanism of Al/La1−xSrxMnO3 resistance random access memory. I. Oxygen vacancy formation in perovskites

The oxygen vacancy formation in half-metallic perovskite LSMO itself plays an interesting role in the resistive switching.