Shinya Kito

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.

Detailed analyses of electric field-induced resistance switching behavior of SrFeO3?x film

We investigated the electric field-induced resistance change of SrFeO3−x film as a candidate for memory material. SrFeO3−x film showed hysteresis in its current–voltage curve and distinct pulse-switching properties. The resistance of the sample can be switched by the pulse voltage with the length of 50 ns. The relaxation time of the voltage analyses revealed that the resistance-switching properties originate from both the oxygen migration and the charge injection process. Based on these properties, we found that the magnetic state can also be changed by the application of the electric field.

Relationship between the Crystallinity and Magnetic Properties of Cr2O3/LiNbO3/Cr2O3 Multi-Layer Materials

The magnetic properties of an artificial multiferroic material, a Cr2O3/LiNbO3/Cr2O3 hetero structure with various-thickness LiNbO3 layers, were investigated. All samples showed ferromagnetism due to the existence of oxygen deficiency or an excess of the Cr2O3 layer in the LNO/Cr2O3 interface. The ferromagnetism of the samples was affected by the crystal orientation of the LiNbO3 layer, and seemed to have a major impact on the magneto-electric behavior of this hetero system.

Influence of magneto-electric coefficient for magnetic and electric charge injection properties in magneto-electric MIS capacitors

We investigated the electric charge injection properties of a floating-gate type metal-insulator Si capacitor having different-ME gate insulators. The samples showed charge-injection type behaviour in capacitance-voltage curves, and it was revealed that the amount of injected charges can be controlled by the application of an external magnetic field. The sample having a high-ME-coefficient gate insulator showed stepwise capacitance-voltage curves unlike the normal one. These results indicate that this capacitor, which employs a magnetic gate insulator, has the potential to be used in multilevel memory by the application of an external magnetic field.

Magnetic and electric field induced resistance change in SrFeO thin film

We have investigated Fe electrode/SrFeO3-x stacking layer as resistance random access memory which is called next generation non-volatile memory. In this stacking system, positive magnetoresistance (MR) due to exchange coupling between Fe electrode and SrFeO3-x layer was observed in initial state. After applying external electric field, in the each resistance state which is high resistance state or low resistance state, MR behaviour was changed from positive MR to negative MR. This behaviour is more likely due to that exchange coupling and the phase of SrFeO3-x layer were changed by electric field and we realized that it is possible to control magnetic property and series of SrFeO3-x phase by using external electric field.

Room Temperature Magneto-electric Effect of Cr2O3/Cr2O3?X/LiNbO3/ Cr2O3?X/ Cr2O3 Hetero structure

Murutiferroics material has been many attention due to which has enhanced magnetoelectric (ME) effect. We suggest stacking thin film which has ME effect material/ferromagnetic material/ferroelectric material/ferromagnetic material/ME effect material structure. We have observrd enhanced ME effect in this stacking thin film. However, the origin of that has not been investigated. In this report, we investigated the relationships between the electric properties and enhanced ME effects.

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.