PHYSICAL REVIEW APPLIED 10, 014004 (2018) Voltage-Controlled Sensitivity of the Spin Seebeck Effect in Pt/Y 3 Fe 5 O 12 /MgO/(PbMg 1/3 Nb 2/3 O 3 ) 0.7 (PbTiO 3 ) 0.3 Multiferroic Heterostructures Yu Wang, 1,2 Weiwei Lin, 2, * Danru Qu, 2 Qinli Ma, 2 Yue Zhang, 2,3 Yufan Li, 2 Shuming Yang, 4 and C. L. Chien 2 1 MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi’an Jiaotong University, Xi’an 710049, China 2 Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA 3 School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China 4 State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China (Received 12 January 2018; revised manuscript received 8 April 2018; published 9 July 2018) The characteristics of pure spin current from the longitudinal spin Seebeck effect are investigated at room temperature in Pt/Y 3 Fe 5 O 12 deposited on the (PbMg 1/3 Nb 2/3 O 3 ) 0.7 (PbTiO 3 ) 0.3 substrate, through which electrostrain can be controllably applied. The applied voltage enables the modification of magnetic anisotropy in the magnetic insulating Y 3 Fe 5 O 12 layer, and thus the sensitivity of the spin Seebeck effect at small magnetic fields, without suppressing the spin Seebeck effect and the inverse spin Hall effect. This is due to the robust intrinsic physical parameters in Pt/Y 3 Fe 5 O 12 . Our results pave the way for the application of voltage-controlled pure spin-current devices. DOI: 10.1103/PhysRevApplied.10.014004 I. INTRODUCTION Pure spin current transporting spin angular momentum without a charge current is a key topic in recent condensed- matter physics. The bilayer structure of Pt/Y 3 Fe 5 O 12 , where Pt is a normal metal (NM) and Y 3 Fe 5 O 12 (YIG) is a ferrimagnetic insulator, is one of the most studied structures for pure spin current phenomena [1–6]. A pure spin current can be thermally generated by the longitudi- nal spin Seebeck effect (LSSE) [1–6] via a temperature gradient applied normal to the Pt/YIG interface. The spin current diffusing into the Pt is detected by converting it to an electric voltage via the inverse spin-Hall effect (ISHE) [1–6]. The discovery of LSSE enables the development of spin caloritronics and may lead to novel applications in heat-sensing and thermal-energy-conversion devices. The advent of multiferroic heterostructures [7–11], encompassing both ferromagnetic and ferroelectric lay- ers, enables new developments and applications with the interplay of straintronics and spintronics. Numerous efforts have been devoted to studying voltage-controlled properties, such as magnetic anisotropy [12–15] and exchange bias [16,17] of the ferromagnetic layer, due to the electrostrain of the ferroelectric layer. Most works on the voltage control of magnetic devices, utilizing the anomalous Hall effect, anisotropic magnetoresistance, giant magnetoresistance, and tunnel magnetoresistance, * wlin@jhu.edu [18–20], are based on spin-polarized charge transport in ferromagnetic metals or semiconductors. However, the influence of electrical voltage on pure spin-current trans- port generated by LSSE has not been addressed so far. In this paper, we show the influence of voltage on the LSSE in Pt/YIG/MgO/PMNT multiferroic heterostruc- tures, where the (PbMg 1/3 Nb 2/3 O 3 ) 0.7 (PbTiO 3 ) 0.3 (PMNT) substrate can generate a sizable electrostrain on the Pt/YIG structure by applying voltage, in which the pure spin current is generated and detected. We find that the elec- trostrain alters the sensitivity of the LSSE at low magnetic fields in the sample, by modifying the magnetic anisotropy of the YIG thin film, without suppression of the LSSE and ISHE. These results demonstrate that when electri- cally tuning the sensitivity, the spin-current transport and spin-charge conversion are robust under eletrostrain in the Pt/YIG, which is advantageous for practical applications of voltage-controlled pure spin-current devices. II. EXPERIMENTS The configuration of our Pt/YIG/MgO/PMNT sample is shown in Fig. 1(a). We use (011)-oriented PMNT sin- gle crystals with size 5 × 5 × 0.2 mm 3 as the piezoelectric substrates. A 1-nm-thick MgO buffer layer and a 40-nm YIG layer are deposited on the PMNT substrate by rf magnetron sputtering at room temperature. The YIG film became magnetic above room temperature after annealing in air at T = 1133 K for 15 min. Subsequently, a 3-nm-thick 2331-7019/18/10(1)/014004(5) 014004-1 © 2018 American Physical Society