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Magnetization and resistance switchings induced by electric field in epitaxial Mn:ZnO/BiFeO3 multiferroic heterostructures at room temperature Dong Li, Wanchao Zheng, Dongxing Zheng, Junlu Gong, Liyan Wang, Chao Jin, Peng Li, and Haili Bai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b11265 • Publication Date (Web): 26 Jan 2016 Downloaded from http://pubs.acs.org on February 1, 2016
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ACS Applied Materials & Interfaces
Magnetization and Resistance Switchings Induced by Electric Field in Epitaxial Mn:ZnO/BiFeO3 Multiferroic Heterostructures at Room Temperature
Dong Li, Wanchao Zheng, Dongxing Zheng, Junlu Gong, Liyan Wang, Chao Jin, Peng Li, and Haili Bai*
Tianjin Key Laboratory of Low Dimensional Materials Physics and Preparing Technology, Institute of Advanced Materials Physics, Faculty of Science, Tianjin University, Tianjin 300072, PRC
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Author to whom all correspondence should be addressed. E-mail:
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ABSTRACT
Electric field induced reversible switchings of the magnetization and resistance were achieved at room temperature in epitaxial Mn:ZnO(110)/BiFeO3(001) heterostructures. The observed modulation of magnetic moment is ~500% accompanying with a coercive field varying from 43 to 300 Oe and a resistive switching ratio up to ~104% with the applied voltages of ±4 V. The switching mechanisms in magnetization and resistance are attributed to the ferroelectric polarization reversal of the BiFeO3 layer under applied electric fields, combined with the reversible change of oxygen vacancy concentration at the Mn:ZnO/BiFeO3 interface.
PACS: 75.70.Cn, 75.50.Pp, 75.85.+t
Keywords: magnetization reversal, multiferroic heterosutructures, magnetoelectric coupling effect, bismuth ferrite, zinc oxide films
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ACS Applied Materials & Interfaces
INTRODUCTION
Multiferroic materials have been proposed to meet the demands for higher memory speed and density with low energy assumption in next generation information technologies and systems.1−5 The converse magnetoelectric (ME) effect makes it possible to control magnetism with electric fields rather than electric currents or magnetic fields, thus achieving electric-writing and magnetic-reading.6 ME coupling in single-phase multiferroics is often too weak and only occurs in very low temperatures, which severely limits its practical application. Up to now, many efforts especially which combines room temperature ferromagnetic (FM) and ferroelectric (FE) materials have been made to explore new possibilities of electrical tunable magnetization in thin film systems.3 For instance, to achieve electric-field control of magnetization in multiferroic materials or structures, ME effects are mainly studied in the exchange bias (EB), strain or charge mediated couplings of transition metal and oxide ferromagnets to ferroelectrics or multiferroics.7−12 To date, electric field control of magnetism by exchange coupling has been accomplished in CoFe/BiFeO3 and La0.7Sr0.3MnO3/BiFeO3 structures.8–10 Even so, the applied in-plane electric field in the CoFe/BiFeO3 structure is unfavorable for high density storage, and the blocking temperature (100 K) of exchange bias in the La0.7Sr0.3MnO3/BiFeO3 structure is much lower than room temperature. In strain mediated FM-FE systems, the piezoelectric strain of the FE layer −3−
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can be transferred to the FM layer, which would result in converse ME effects.11, 12 But the induced strain effect is hard to retain without continuous voltage. Remnant polarization as a dual effect offers the possibility of nonvolatile and reversible switching of magnetization and resistance in the charge-mediated ME systems.13, 14 Charge carriers are repelled or attracted by ferroelectric polarization, which will change the charge-related magnetic and electronic transport properties. BiFeO3 (BFO) is one of the most potential lead-free ferroelectric materials and the only room-temperature multiferroic material.9, 15 The discovery of its high remnant polarization in thin films has attracted much close attention for its great potential applications in nonvolatile memory and spintronics.16−20 Recently, tetragonal-like BiFeO3 (T-BFO) films have been unveiled a giant polarization up to 150 µC/cm2, which is related to its large axial ratio ( c / a ≈ 1.24 ).21, 22 T-BFO films can be fabricated in highly strained films (e.g.
