Pure Spin Transport in YIG-based structures

Y3Fe5O12 (YIG) is one of the best materials for magnetic resonance due to its extremely low magnetic damping. This is particularly attractive for generating pure spin currents from YIG into a broad range of materials.  Using off-axis UHV sputtering, we have grown YIG epitaxial thin films with state-of-the-art quality, as shown in the x-ray diffraction scans below. 

Garnet lattice of YIG

Garnet lattice of YIG

X-ray diffraction scans of epitaxial YIG films on GGG

X-ray diffraction scans of epitaxial YIG films on GGG

We observe exceptionally large ferromagnetic resonance (FMR) spin pumping signals in YIG/metal bilayers using inverse spin Hall effect (ISHE) [in collaboration with Prof. Hammel’s group]. During the spin pumping process, the ferrimagnetic YIG is excited by a microwave field and its precessing magnetization allows for transfer of angular momentum to the conduction electrons in Pt, producing a pure spin current without an accompanying charge current. The pure spin current is converted to a net charge current in Pt via the ISHE.

Schematic of IISHE measurement

SISHE measurement

ISHE voltages generated by FMR spin pumping in 12 metals including 3d, 4d and 5d transition metals.

ISHE voltages generated by FMR spin pumping in 12 metals including 3d, 4d and 5d transition metals.

The observed giant spin pumping signal indicate that: (1) the spin injection efficiency can be significantly improved by using high crystalline quality ferromagnets, (2) the critical role of the interface in spin transfer, (3) the ceiling for the magnitude of pure spin currents can be dramatically imcreased, making this intriguing phenomenon highly attractive for applications.

The high-efficiency YIG spin pumping allows detection of 1000-fold exponential decay of spin pumping from YIG to Pt across insulating barriers,  confirming exchange coupling as the underlying mechanism for spin pumping. We achieve robust spin transport from YIG to Pt across an antiferromagnetic insulator NiO, which strikingly enhances the ISHE signals at thin NiO thicknesses and can transmit spin currents up to 100 nm NiO thickness, demonstrating highly efficient spin transport through an antiferromagnetic insulator.

ISHE voltage as a function of the SrTiO3 barrier thickness for YIG/SrTiO3/Pt(5 nm) trilayers. (b) NiO thickness dependencies of the ISHE voltages for YIG(20 nm)/NiO(tNiO)/Pt(5 nm) trilayers.

ISHE voltage as a function of the SrTiO3 barrier thickness for YIG/SrTiO3/Pt(5 nm) trilayers. (b) NiO thickness dependencies of the ISHE voltages for YIG(20 nm)/NiO/Pt(5 nm) trilayers.

 

References:

  1. H. L. Wang, C. H. Du, P. C. Hammel and F. Y. Yang, “Antiferromagnonic Spin Transport from Y3Fe5O12 into NiO,” Phys. Rev. Lett. 132, 097202 (2014).      DOI: http://dx.doi.org/10.1103/PhysRevLett.113.097202
  2. H. L. Wang, C. H. Du, P. C. Hammel and F. Y. Yang, “Spin Current and Inverse Anomalous Hall Effect in Ferromagnetic metals Probed by Y3Fe5O12-Based Spin Pumping,” Appl. Phys. Lett. 104, 202405 (2014).     DOI: http://dx.doi.org/10.1063/1.4878540
  3. C. H. Du, H. L. Wang, F. Y. Yang, and P. C. Hammel, “Enhancement of Pure Spin Currents in Spin Pumping Y3Fe5O12/Cu/metal Trilayers through Spin Conductance Matching,” Phys. Rev. Applied 1, 044004 (2014).     DOI: http://dx.doi.org/10.1103/PhysRevApplied.1.044004
  4. H. L. Wang, C. H. Du, P. C. Hammel, and F. Y. Yang, “Scaling of spin Hall angle in 3d, 4d and 5d metals from Epitaxial Y3Fe5O12/metal spin pumping,” Phys. Rev. Lett. 112, 197201 (2014).     DOI: http://dx.doi.org/10.1103/PhysRevLett.112.197201
  5. C. S. Wolfe, V. P. Bhallamudi, H. L. Wang, C. H. Du, S. Manuilov, A. J. Berger, R. Adur, F. Y. Yang, and P. C. Hammel, “Off-Resonant Manipulation of Spins in Diamond via Precessing Magnetization of a Proximal Ferromagnet,” Phys. Rev. B 89, 180406(R) (2014).     DOI: http://dx.doi.org/10.1103/PhysRevB.89.180406
  6. H. L. Wang, C. H. Du, P. C. Hammel, and F. Y. Yang, “Strain-Tunable Magnetocrystalline Anisotropy in Epitaxial Y3Fe5O12Thin Films,” Phys. Rev. B 89, 134404 (2014).     DOI: http://dx.doi.org/10.1103/PhysRevB.89.134404
  7. C. H. Du, H. L. Wang, Y. Pu, T. L. Meyer, P. M. Woodward, F. Y. Yang, and P. C. Hammel, “Probing the Spin Pumping Mechanism: Exchange Coupling with Exponential Decay in Y3Fe5O12/barrier/Pt Heterostructures,” Phys. Rev. Lett. 111, 247202 (2013).     DOI: http://dx.doi.org/10.1103/PhysRevLett.111.247202
  8. H. L. Wang, C. H. Du, Y. Pu, R. Adur, P. C. Hammel, and F. Y. Yang, “Large spin pumping from epitaxial Y3Fe5O12 thin films to Pt and W layers,” Phys. Rev. B Rapid Comm. 88, 100406(R) (2013).     DOI: http://dx.doi.org/10.1103/PhysRevB.88.100406