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Trinity College Dublin

Material Advances in Spintronics and Magnetic Recording

Phys. Status Solidi B 248, No. 10, 2338–2344 (2011)

There is an increasing demand for magnetic materials that exhibit high perpendicular anisotropy to assure thermal stability in nano-scale spintronic devices. Spin-transfer-torque (STT) memory applications require switching current densities of order 109Am_2 to facilitate reliable switching. A magnetic material which exhibits low magnetization and high perpendicular anisotropy combined with high spin polarization is an ideal combination for STT memories. Magnetic recording applications, on the other hand, require materials that exhibit high magnetization with high perpendicular anisotropy to maintain thermal stability in sub-10 nm bits.

In this research tetragonal Mn3-xGa (0≤x≤1) epitaxial films that possess exceptional magnetic and electronic properties are explored. Stoichiometric Mn3Ga crystallizes in the D022 structure and is a collinear ferrimagnet with an easy c-axis. It exhibits a unique combination of low magnetization, high uniaxial anisotropy, high Curie temperature and high spin polarization, which suit the requirements for spin torque memories down to 10 nm in size. Mn2Ga, on the other hand, exhibits much higher magnetization, high perpendicular anisotropy and high Curie temperature but a lower spin polarization, which make it a potential candidate for high density bit-patterned recording with areal densities up to 10 Tb inch_2 (_15 kbmm_2) and 10-year thermal stability. The flexibility of the D022 structure allows a variety of magnetic materials to be synthesized with varying x to suit specific magnetic applications, additionally hexagonal D019-Mn3Ga films are antiferromagnetic, which could be useful for exchange bias.

The high anisotropy combined with low magnetization and high spin polarization of ferromagnetic Mn3Ga can open ways to realize thermally stable solid state magnetic memories switched by spin torque, which can possibly compete with flash memory.

Figure: (a) The tetragonal D022 unit cell of Mn3Ga. Ga atoms are ordered in a body-centred tetragonal structure and Mn atoms occupy 2b (red) and 4d (green) sites. (b) The hexagonal D019 unit cell of Mn3Ga