Shotaro Murata

Electric field-induced magnetic changes in La0.7Sr0.3MnO3 thin film using electric field-induced resistance phenomenon

We achieved the electrical control of a magnetic state by using an external magnetic field via electric field-induced resistance (EIR) change phenomena. We prepared a La0.7Sr0.3MnO3 (LSMO) film which showed EIR changes. Before the EIR treatment, the sample barely showed negative magnetoresistance (MR). After the EIR treatment, the value of negative MR became six times larger than that before the EIR treatment. The magnetization curves also changed from paramagnetism to superparamagnetism. These behaviors revealed that the EIR treatment changed not only the resistance state but also the magnetic state in LMSO film.

Preparation and Exchange Bias of a Cr2O3/(La0.7Sr0.3)MnO3 Magnetic Hetero Junction

We investigated the magnetic interaction between antiferromagnetic, magnetoelectric Cr2O3 film and ferromagnetic La0.7Sr0.3MnO3 film, which shows colossal magneto-resistance. Magnetic properties and structural analyses revealed that a decrease in the thickness of La0.7Sr0.3MnO3 films gives rise to a change in magnetic anisotropy from perpendicular to in-plane. The exchange interaction between Cr2O3 and La0.7Sr0.3MnO3 also changed depending on the magnetic properties of La0.7Sr0.3MnO3. This suggests that the crystallographical control and the selection of a suitable thickness of La0.7Sr0.3MnO3 are important to obtain an exchange interaction in the magnetic hetero system using colossal magneto-resistance material.

Relationships between Negative Differential Resistances and Resistance Switching Properties of SrFeO2+x Thin Films with Excess Oxygen

Resistance random access memory (RRAM) is attractive as a next-generation form of nonvolatile memory. We investigated an electric field-induced resistance change of SrFeO2+x film as a candidate for RRAM material. SrFeO2.5-x film prepared at 300 oC showed hysteresis in its current-voltage curve and distinct pulse-switching properties. On the other hand, the sample prepared below 280 oC showed hysteresis in its current-voltage curve but didn’t show pulse-switching properties. The amount of oxygen in the sample and easiness of oxygen migration play important roles in the resistance-switching properties.

Magnetic and Dielectric Properties of Cr2O3/LiNbO3/Cr2O3 Multi Layer

We proposed a new type of multi-ferroic system using magnetoelectric (ME:Cr2O3) material/ultra-thin ferroelectric materials (FE)/a magnetoelectric material hetero structure. This ME and FE heterosystem showed a general Polarization – Electric field hysteresis curve. When a magnetic and electric field (ME field) was applied at the same time, a decrease of polarization was observed. This might be due to the antiferromagnetic domain alignment of Cr2O3 by the ME field.

Influence of an External Magnetic Field on Injected Charges of a Cr2O3/Fe/CeO2/Si MIS Capacitor

We investigated the influence of an external magnetic field for the carrier injection process of a metal (Au) / insulator (Cr2O3/Fe/CeO2) / semiconductor (Si) (MIS) capacitor, in which the insulator consists of magnetic materials. By applying an electric field, electrons propagating through the CeO2 layer from Si were injected into the Fe or an oxygen deficiency layer formed around the Fe layer. When a magnetic field was applied, the hysteresis window width of this capacitor was reduced. I-V curve analyses under a magnetic field revealed that this reduction was more likely due to the magnetic state of the Fe layer and the interaction between Fe and Cr2O3.

Resistance Changes of (La, Sr)MnO3 Thin Film via Exchange Bias Tuning by the Application of an External Electric Field

We have investigated the relationships between the electric field-induced resistance change and the strength of the exchange interaction of the Cr2O3/ La0.7Sr0.3MnO3 (LSMO) magnetic hetero system. The hetero system subjected to field cooling (FC) showed a positive shift in the magnetization curves due to an exchange bias. The exchange bias field changed depending on the FC field. Resulting from the exchange behaviors, the resistance of LSMO film was changed by the application of an electric field to the Cr2O3 gate. This resistance change is more likely due to the interface interaction strength between the Cr2O3 and LSMO film

Relationship between magneto-capacitance-voltage characteristics and magnetoresistance of Au∕Cr2O3∕Cr2O3−x∕FeCr∕CeO2∕Si metal-insulator-semiconductor capacitor

We investigated the relationship between the magneto-capacitance-voltage characteristics and the magnetoresistance of a metal (Au)/insulator (Cr2O3∕Cr2O3−x∕FeCr∕CeO2)/semiconductor (Si) capacitor, in which the insulator consists of magnetic materials. By applying an electric field, electrons propagating through the FeCr∕CeO2 layer from Si were injected into the Cr2O3−x layer. When a magnetic field was applied, the resistance of this capacitor above the flat-band voltage was reduced, causing the hysteresis window to become large. This result indicates that this capacitor, which contains a magnetic gate insulator, has the potential to be used in multilevel memories by the application of an external magnetic field.