Spin-transfer driven dynamics in hybrid structures


Spin-transfer driven dynamics in hybrid structures

Fowley, C.; Rode, K.; Gallardo, R.; Thiyagarajah, N.; Lau, Y.-C.; Borisov, K.; Betto, D.; Atcheson, G.; Kampert, E.; Wang, Z.; Lindner, J.; Coey, M.; Stamenov, P.; Deac, A. M.

Since the discovery of giant magnetoresistance, metal spintronics has seen unprecedented advances, from the realisation of ultra-high magnetoresistance ratios to substantial output power from both conventional spin transfer torque oscillators as well as spin-torque vortex oscillators [1]. The recently discovered of the fully compensated ferrimagnetic half-metal, manganese ruthenium gallium (MRG), due to its widely tunable magnetic properties [2], could enable spin torque oscillators which work in the range of hundreds of GHz. Being a ferrimagnet, MRG consists of two magnetic sublattices which are coupled antiferromagnetically to each other. It has been shown that in this material the magnetotransport is dominated by one magnetic sublattice whereas the overall magnetisation is determined by both sublattices [3]. This means that MRG behaves magnetically like an antiferromagnet and electrically like a highly spin polarised ferromagnet, implying that spin-transfer torque would act on one sublattice only, enabling efficient current induced excitations. Due to the different temperature dependences of the sublattice magnetisations, MRG displays a compensation temperature at which the total magnetic moment is zero and the magnetic state is impervious to external magnetic fields [4].
Here we conduct high-field magnetotransport measurements [5] on selected films of MRG with differing Ru concentration and, therefore, different compensation temperatures (Tc). Both the transverse Hall resistivity and longitudinal resistivity are recorded in magnetic fields up to 58T. MRG exhibits a large spontaneous Hall angle of ~2%, coercivity exceeding 1T at room temperature (and several Teslas close to Tc) and has very low net magnetisation of 25kA/m. Despite having a no net magnetic moment at the compensation temperature the magnitude of the Hall signal does not become zero, further indicating both the half-metallic nature of the material and that the magnetotransport is dominated by one sublattice only. An additional feature is observed in the transport data, which resembles a spin-flop transition. By comparison to analytical and mean-field calculations of the sublattice magnetisation directions we can estimate the both the sublattice anisotropy (Hk) and interlayer exchange coupling (Hex). The out-of-phase and in-phase magnetic resonance modes, therefore, lie in the range of 0.3THz and 4THz, respectively. This makes MRG a uniquely tuneable material as a free layer in spin-transfer oscillator applications [6].

References:

[1] Baibich M.N. et al., Physical Review B, 61, 2472 (1988), Ikeda S. et al., Applied Physics Letters, 93 082508 (2008), Tsunegi S. et al., Applied Physics Letters, 109, 252402 (2016)
[2] Kurt H. et al., Physical Review Letters, 112, 027201 (2014)
[3] Borisov K. et al., Applied Physics Letters, 108, 192407 (2016)
[4] Betto D. et al., AIP Advances, 6, 055601 (2016)
[5] Fowley C. et al., Journal of Physics D : Applied Physics, 48, 164006 (2015)
[6] Awari N. et al., Applied Physics Letters, 109, 032403 (2016)

Keywords: magnetism; spin-transfer torque; wireless communication

Related publications

  • Invited lecture (Conferences)
    Moscow International Symposium on Magnetism, 01.-05.07.2017, Moscow, Russia

Permalink: https://www.hzdr.de/publications/Publ-26032
Publ.-Id: 26032