Heat-driven engines are hard to realize in nanoscale machines because of efficient heat dissipation1. However, in the realm of spintronics, heat has been employed successfully—for example, heat current has been converted into a spin current in a NiFe|Pt bilayer system2, and Joule heating has enabled selective writing in magnetic memory arrays3. Here, we use Joule heating in nanoscale magnetic tunnel junctions to create a giant spin torque due to a magnetic anisotropy change. Efficient conversion from heat dynamics to spin dynamics is obtained because of a large interfacial thermal resistance at an FeB|MgO interface. The heat-driven spin torque is equivalent to a voltage-controlled magnetic anisotropy4,5 of approximately 300 fJ V−1 m−1, which is more than twice the value reported in a (Co)FeB|MgO system6,7. We demonstrate an electric microwave amplification gain of 20% in a d.c. biased magnetic tunnel junction as a result of this spin torque. While electric d.c. power amplification in spintronic devices has been realized previously8, the microwave amplification was limited to relatively small amplification gains (G = radiofrequency output voltage/radiofrequency input voltage) and has never exceeded 1 (refs 9,10,11,12,13). A magnetic tunnel junction driven by radiofrequency spin transfer torque using ferromagnetic resonance enabled a relatively large gain of G ≈ 0.55 (ref. 12). Furthermore, radiofrequency spin waves were tuned by the spin transfer effect14,15. The heat-driven giant spin torque in the FeB|MgO16,17 magnetic tunnel junction, which shows a large magnetization precession and resistance oscillation under a d.c. bias, overcomes the above limitations and provides a gain larger than 1.
Subscribe to Journal
Get full journal access for 1 year
only $15.58 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
Feynman, R. P. There’s plenty of room at the bottom. Eng. Sci. 23, 22–36 (1960).
Uchida, K. et al. Observation of the spin Seebeck effect. Nature 455, 778–781 (2008).
Beech, R. S., Anderson, J. A., Pohm, A. V. & Daughton, J. M. Curie point written magnetoresistive memory. J. Appl. Phys. 87, 6403 (2000).
Weisheit, M. et al. Electric field–induced modification of magnetism in thin-film ferromagnets. Science 315, 349–351 (2007).
Maruyama, T. et al. Large voltage-induced magnetic anisotropy change in a few atomic layers of iron. Nat. Nanotech. 4, 158–161 (2009).
Nozaki, T. et al. Voltage-induced magnetic anisotropy changes in an ultrathin FeB layer sandwiched between two MgO layers. Appl. Phys. Express 6, 073005 (2013).
Li, X. et al. Enhancement of voltage-controlled magnetic anisotropy through precise control of Mg insertion thickness at CoFeB|MgO interface. Appl. Phys. Lett. 110, 052401 (2017).
Konishi, K. et al. Current-field driven ‘spin transistor’. Appl. Phys. Express 2, 063004 (2009).
Kasai, S. et al. Three-terminal device based on the current-induced magnetic vortex dynamics with the magnetic tunnel junction. Appl. Phys. Express 1, 091302 (2008).
Nozaki, T. et al. RF amplification in a three-terminal magnetic tunnel junction with a magnetic vortex structure. Appl. Phys. Lett. 95, 022513 (2009).
Tomita, H., Maehara, H., Nozaki, T. & Suzuki, Y. Negative dynamic resistance and rf amplification in magnetic tunnel junctions. J. Magn. 16, 140–144 (2011).
Xue, L. et al. Conditions for microwave amplification due to spin–torque dynamics in magnetic tunnel junctions. Appl. Phys. Lett. 99, 022505 (2011).
Konishi, K. et al. Radio-frequency amplification property of the MgO-based magnetic tunnel junction using field-induced ferromagnetic resonance. Appl. Phys. Lett. 102, 162409 (2013).
Kajiwara, Y. et al. Transmission of electrical signals by spin-wave interconversion in a magnetic insulator. Nature 464, 262 (2010).
Evelt, M. et al. High-efficiency control of spin-wave propagation in ultra-thin yttrium iron garnet by the spin–orbit torque. Appl. Phys. Lett. 108, 172406 (2016).
Kubota, H. et al. Enhancement of perpendicular magnetic anisotropy in FeB free layers using a thin MgO cap layer. J. Appl. Phys. 111, 07C723 (2012).
Miwa, S. et al. Highly sensitive nanoscale spin–torque diode. Nat. Mater. 13, 50–56 (2014).
Nozaki, T. et al. Electric-field-induced ferromagnetic resonance excitation in an ultrathin ferromagnetic metal layer. Nat. Phys. 8, 491–496 (2012).
Zhu, J. et al. Voltage-induced ferromagnetic resonance in magnetic tunnel junctions. Phys. Rev. Lett. 108, 197203 (2012).
Yuasa, S., Nagahama, T., Fukushima, A., Suzuki, Y. & Ando, K. Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions. Nat. Mater. 3, 868–871 (2004).
Parkin, S. S. P. et al. Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers. Nat. Mater. 3, 862–867 (2004).
Kiselev, S. I. et al. Microwave oscillations of a nanomagnet driven by a spin-polarized current. Nature 425, 380–383 (2003).
Ishibashi, S. et al. Large diode sensitivity of CoFeB/MgO/CoFeB magnetic tunnel junctions. Appl. Phys. Express 3, 073001 (2010).
Petit, S. et al. Spin-torque influence on the high-frequency magnetisation fluctuations in magnetic tunnel junctions. Phys. Rev. Lett. 98, 077203 (2007).
Tulapurkar, A. A. et al. Spin-torque diode effect in magnetic tunnel junctions. Nature 438, 339–342 (2005).
Böhnert, T. et al. Influence of the thermal interface resistance on the thermovoltage of a magnetic tunnel junction. Phys. Rev. B. 95, 104441 (2017).
Shiota, Y. et al. Induction of coherent magnetisation switching in a few atomic layers of FeCo using voltage pulses. Nat. Mater. 11, 39–43 (2012).
Kanai, S. et al. Electric field-induced magnetisation reversal in a perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction. Appl. Phys. Lett. 101, 122403 (2012).
Grezes, C. et al. Ultra-low switching energy and scaling in electric-field-controlled nanoscale magnetic tunnel junctions with high resistance-area product. Appl. Phys. Lett. 108, 012403 (2016).
Kozioł-Rachwał, A. et al. Enhancement of perpendicular magnetic anisotropy and its electric field-induced change through interface engineering in Cr/Fe/MgO. Sci. Rep. 7, 5993 (2017).
This research was supported by Bilateral Programs (MEXT), MIC, the ImPACT programme of the Council for Science, Technology, and Innovation (Cabinet Office, Government of Japan) and JSPS KAKENHI (grant no. JP16H03850).
The authors declare no competing interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Goto, M., Wakatake, Y., Oji, U.K. et al. Microwave amplification in a magnetic tunnel junction induced by heat-to-spin conversion at the nanoscale. Nature Nanotech 14, 40–43 (2019). https://doi.org/10.1038/s41565-018-0306-9
Physica B: Condensed Matter (2020)
Nature Communications (2020)
Origin of the Resistance-Area-Product Dependence of Spin-Transfer-Torque Switching in Perpendicular Magnetic Random-Access Memory Cells
Physical Review Applied (2020)
Magnetodynamics in orthogonal nanocontact spin-torque nano-oscillators based on magnetic tunnel junctions
Applied Physics Letters (2019)
Nature Nanotechnology (2019)