Observation of Fe/BaTiO₃Interface State by X-Ray Absorption Spectroscopy

Abstract

Electric field-induced change of magnetic properties in ferromagnetic Fe thin film grown on a ferroelectric BaTiO3 (BTO) substrate is studied by means of x-ray absorption spectroscopy. We find that a few nm Fe oxide layer exists at the Fe/BTO interface when the Fe thickness is 8 nm, in which the film shows in-plane magnetization. The x-ray magnetic circular dichroism analysis reveals that the coercive field, Hc, of Fe shows a hysteresis behavior as a function of the electric field, and larger Hc is observed at ∼ ±3 kV/cm. On the other hand, it is found from the extended x-ray absorption fine structure analysis that the Fe-O bond distance shows a similar electric field dependence to that of Hc, and shorter distance is observed at ∼ ±3 kV/cm. Therefore, it is assumed that the Hc strongly depends on the ferroelectric domain structure of BTO, and larger Hc is observed for the multidomain structure. We suppose that shrinking of the Fe-O distance caused by the domain formation leads to an enhancement of Hc due to the island-like localization of the interface Fe oxide.

Effect of Electric Field on Magnetism of Ni Thin Films via Antiferromagnetic NiO

“…On the other hand, it was reported that the coercive field of a ferromagnetic Fe thin film grown on a ferroelectric BaTiO 3 (BTO) substrate is modified by voltage application between the Fe film and the bottom of the BTO substrate [2]. Moreover, we have recently investigated the electric field-induced changes in magnetic properties for Fe/BTO by means of X-ray absorption spectroscopy (XAS) [3]. It has been revealed that a few nmthick Fe oxide layer exists at the Fe/BTO interface, and that it plays an essential role in the electric-field effects, which suggests that a ferromagnetic/antiferromagnetic coupling could be altered by electric fields.…”

Voltage-Induced Changes in Magnetism of FeCo/BaTiO₃Thin Films Studied by X-Ray Absorption Spectroscopy

“…On the other hand, it was reported that the coercive field of ferromagnetic Fe thin film grown on a ferroelectric BaTiO 3 (BTO) substrate changes when a voltage is applied between the Fe film and the bottom of the substrate even at RT [3]. Moreover, we have observed a slight change in the X-ray magnetic circular dichroism (XMCD) spectrum depending on the sign and magnitude of the applied voltage [4]. In the present study, we investigate the voltage-induced changes in the magnetic properties of FeCo thin films grown on the BTO substrate.…”

“…This is probably due to the increase in the magnetic component which has a larger coercive field. Since BTO is known to exhibit a lattice expansion along the applied electric field, the observed voltage-induced change in the Fe 67 Co 33 film might be attributed to the structural change, such as the formation of domain structure, of the BTO substrate, which is suggested in the 8 nm Fe film [4]. On the other hand, the magnetization curves for the Fe 50 Co 50 film exhibit larger hysteretic behavior at positive electric fields.…”

Effect of interface NiO layer on magnetism in Fe/BaTiO3 thin film

“…We have recently found from X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) that an Fe oxide component exists near the interface, and that it closely correlates with the field-induced magnetic change in Fe. 16) In this study, we insert an interface NiO layer between the Fe thin film and BaTiO 3 for realizing peculiar interface phenomena, such as the ferromagnetic=antiferro-magnetic coupling between Fe and NiO. Although our final goal is to utilize such interfacial effect and apply it to the field effect, here, we concentrate on the investigation of the effect of the interface NiO layer on the magnetism of Fe=BaTiO 3 by using XMCD and extended X-ray absorption spectroscopy (EXAFS), and a possible interfacial structure is discussed.…”