Probing antiferromagnets with currents

Rafael L. Seeger

The paradigm shift consisting of using the spin-dependent transport properties of antiferromagnets in electronics led to many exciting challenges.1),2)In this talk, we will first discuss the nature of a spin current flowing through fluctuating antiferromagnets and distinguish between electronic and magnonic spin transport. The method used to inject the spin currents involved ferromagnetic resonance and spin pumpingin ferromagnetic-spin-injector/(non-magnetic-spin-conductor)/antiferromagnetic-spin-sink multilayers. Three typical cases will be presented, magnonic spin flow in the insulating antiferromagnets NiO and NiFeOx, electronic spin flow in the metallic antiferromagnet IrMn, and electronic and magnonic parallel spin flows in IrMn when the latter is directly exchange coupled to the ferromagnetic-spin-injector. In this latter case, how it is possible to unravel the spin injection efficiency of the two types of spin flows will be demonstrated. We will also demonstrate how linear spin fluctuations enhance spin injection in spin-sinks(Fig. 1)and show why this is pertinent for studies ofcritical phenomenon like magnetic phase transitions in ultra-thin films. To show the far-reaching practical relevance of the method, extension to various phase transitions will be presented.3)-6)In search for spin fluctuations in several antiferromagnetic spin-sinks, we will also discuss how we found experimental evidence the impact of eddy-currents7)and of self-induced spin-charge conversion in the spin-injector, corroborating the results of first-principle calculations.8),9)Beyond spin currents, we will finally present a stimulating example of how antiferromagnets and superconductors may envision a common future by showing how to infer essential information about domain walls using Cooper pairs through antiferromagnets.10),11)

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[2] V. Baltz et al, Rev. Mod. Phys. 90, 015005 (2018)
[3] Y. Ohnumaet al, Phys. Rev. B 89, 174417 (2014)
[4] L. Frangou et al, Phys. Rev. Lett. 116, 077203 (2016)
[5] Z. Qiu et al, Nat. Commun. 7, 12670 (2016)
[6] O. Gladii et al, Phys. Rev. B 98, 094422 (2018) ; Appl. Phys. Express 12, 023001 (2019)
[7] R. L. Seeger et al, Appl. Phys. Lett. 115, 032403 (2019)
[8] A. Tsukahara et al, Phys. Rev. B 89, 235317 (2014)
[9] O. Gladii et al, Phys. Rev. B 100, 1174409 (2019)
[10] A. I. Buzdin, Rev. Mod. Phys. 77, 935 (2005)
[11] R. L. Seeger et al, in preparation(2020)