1. Electric field manipulation of magnetization at room temperature in multiferroic CoFe 2 O 4 /Pb(Mg 1/3 Nb 2/3 ) 0.7 Ti 0.3 O 3 heterostructures J. J. Yang, 1 Y. G. Zhao, 1,a) H. F. Tian, 1 L. B. Luo, 1 H. Y. Zhang, 1 Y. J. He, 1 and H. S. Luo 2 1 Department of Physics and State Key Laboratory of New Ceramics and Fine Processing, Tsinghua University, Beijing 100084, People ’ s Republic of China 2 State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 201800, People ’ s Republic of China  Multiferroic materials and multiferroic heterostructures: I. Introduction and objective  CoFe 2 O 4 /Pb(Mg 1/3 Nb 2/3 ) 0.7 Ti 0.3 O 3 (CFO/PMN-PT) heterostructures: Considering the large magnetostriction of CFO and excellent piezoelectric activity of PMN-PT single crystal, the CFO/PMN-PT heterostructure is a good candidate for the study of ME coupling effect. However, there have been no reports on CFO/PMN-PT heterostructure. We have fabricated the CFO/PMN-PT heterostructures and studied the properties of electric field control of magnetization.  Objective II. Methods  CFO films were grown on PMN-PT (001) substrate by PLD. The thickness of the films is about 200 nm.  The magnetization of the CFO films was measured by a SQUID (MPMS- XL7). The voltage was applied in situ on the sample by an electrometer (6517A, Keithley) during the magnetic measurement. III. XRD and magnetic property of the multiferroic CFO/PMN-PT heterostructures.  XRD data show that CFO films are single-phase and (004) oriented.  The in-plane and out-of-plane magnetic hysteresis loops of CFO films show that a small magnetic anisotropy exists with the out-of-plane direction as the magnetic hard direction. This is consistent with the in- plane stress anisotropy energy E=K me cos 2 θ, where anisotropy constant K me = -3λ 100 σ 100 /2, λ 100 = -350×10 -6 for CFO films and σ 100 <0 for compression. IV. Electric field control of the magnetic anisotropy of CFO films in CFO/PMN-PT heterostructures V. Electric field manipulation of magnetization in CFO/PMN-PT heterostructures Publication: Appl. Phys. Lett. 94, 212504 (2009)  In-plane (out-of-plane) magnetizati- on of CFO films increases (decreases) under out-of-plane electric field and restores to its initial values after removal of the electric field.  The electric field elongate the out-of- plane lattice parameter of PMN-PT through the converse piezoelectric effect and thus enhances σ 100, resulting in an increase in K me. As a result, the in-plane (out-of-plane) magnetization increases (decreases) under electric field.  The in-plane and out-of-plane Δ M/M(0)−Electric field loops have butterfly shape, which agree with the strain-electric field loop of PMN-PT single crystal. And the derived maximal ME coupling coefficient α=μ 0 dM/dE is 3.2×10 −8 s m −1.  The manipulation of magnetization of CFO films by electric voltages with different polarities was realized. The manipulation of magnetization is reversible and the change of magnetization is sharp. These are also consistent with the in-plane stress anisotropy energy.  The sharp and reversible ME coupling coefficient α=μ 0 dM/dE is 2.5×10 −8 s m −1. These values is comparable to that of CoFe 2 O 4 nanopillars in a BiFeO 3 matrix (~10 −8 s m −1 ). VI. Conclusion  The manipulation of magnetization by electric field at room temperature was realized. And the results can be understood by the picture of electric field control of magnetic anisotropy.  A large ME coupling coefficient was observed in the multiferroic CFO/PMN-PT heterostructures, which is comparable to that of CoFe 2 O 4 nanopillars in a BiFeO 3 matrix (~10 −8 s m −1 ). Multiferroic materials with magnetoel- ectric (ME) coupling have attracted much attention due to their interesting properties and potential applications. Because single phase multiferroic materials are rare, multiferroic heter- ostructures provide an alternative way for exploring ME effect via accurately controlled interface. In these studies, one of the key issues is the manipulation of magnetism by electric field and the work on this aspect is still limited.