1. Spintronics with ferrimagnetic and antiferromagnetic materials

Compared with traditional ferromagnet, zero moment magnetic materials (antiferromagnet or ferrimagnet) have the advantages of faster dynamics, more robustness against external perturbation and better data security.

Rare earth-transition metal alloy is a category of ferrimagnetic materials which can exhibit compensated magnetic moment, as the spins of rare earth and transition metal atoms align antiparallelly with each other.

In Co1-xTbx alloys, the transport properties are dominated by Co atoms. Therefore, a non-zero magnetoresistance and hall resistance can be detected even in the magnetically compensated alloy. Spin Hall effect and spin orbit torque can be used to switch the orientation of these alloys.

Reference:

• Jungwirth, X. Marti, P. Wadley, and J. Wunderlich, Nat. Nanotechnol. 11, 231 (2016).
• Baltz1, A. Manchon, M. Tsoi, T. Moriyama, T. Ono, and Y. Tserkovnyak, arxiv 1606.04284 (2016)

2. Inducing magnetic dynamics with topological materials

Topological materials (insulators or semimetals) have strong spin orbit interactions. Spin-momentum locked states exist at the surface or interface of these materials. Using these surface states, one can induce spin accumulation, which can be further used to switch the orientation or induce dynamics of adjacent ferromagnetic layers.

A three terminal magnetic tunnel junction can be fabricated using topological material and ferromagnetic films. The topological material can be made into a nanowire geometry and charge current will flow along this nanowire. The induced spin at topological insulator/ferromagnet interface can switch the orientation of magnetic moment. The state (‘1’ or ‘0’) will be read out as the resistance of the tunnel junction.

Reference:

• Fan, Y. et al, Nature Mater. 13, 699-704, (2014).
• Mellnik, A. et al, Nature 511, 449-451, (2014).
• Liu, L. Phys. Rev. B 91, 235437, (2015).

3. Spintronics with 2D materials

2D materials (graphene, transition metal dicolgenide, etc) have many unique spin related properties. Long spin relaxation length or spin relaxation time are expected from those materials. At the same time, unlike 3D material, the diffusion of electron spin in a channel made from 2D material will not decay as a function of 1/r^2. Finally, the 2D geometry makes it easier to electrically manipulate the spin states via the interface Rashba interactions, which can be useful as the building block for spin based FET.