Lecture II Antiferromagnetic Spintronics Alireza Qaiumzadeh Radboud University (RU) Institute for Molecules and Materials (IMM) Theory of Condensed Matter group (TCM)
Interesting but useless! Nobel Lectures in Physics Louis Néel (1904 2000) Antiferromagnetism L. Néel, Ann. de physique (Paris), 17, 63 (1932). L. Néel, Ann. de physique (Paris), 5, 232 (1936). F. Bitter, Phys.Rev., 54, 79 (1938). Ferrimagnetism L. Néel, Ann. de physique (Paris), 3, 137 (1948). T. Jungwirth et al. arxiv: 1509.05296
Paramagnets: very frequent Disordered M=0: bad for directmanipulation by magnetic field, no magnetic memory compatible with semiconductors: transitsors & photonics Antiferromagnets: frequent Ordered M=0: bad for direct manipulation by magnetic field, good for retention with magnetic field around compatible with semiconductors: transitsors & photonics Ferromagnets: rare E exchange Ordered M 0: good for direct manipulation by magnetic field, bad for retention with magnetic field around not well compatible with semiconductors Jungwirth E gap E Fermi
OUTLINE I. Introduction II. AFM-LLG equation III. AFM Domain Wall dynamics (AFM-DWs)
1. Introduction
Magnetic semiconductors: more AFMs than FMs and high-t N AFMs Jungwirth, Novák, Martí et al. PRB 11, Cava Viewpoint, Physics 11, Máca, Mašek, TJ et al. JMMM 12 II VI FM T C (K) AFM T N (K) MnO 122 MnS 152 MnSe 173 MnTe 323 EuO 67 EuS 16 EuSe 5 EuTe 10 I VI III VI FM T C (K) AFM T N (K) CuFeO 2 11 CuFeS 2 825 CuFeSe 2 70 CuFeTe 2 254 III V FMT C (K) AFM T N (K) FeN 100 FeP 115 FeAs 77 FeSb 100 220 GdN 72 GdP 15 GdAs 19 GdSb 27 II V IV V FMT C (K) AFM T N (K) MnSiN 2 490 I II V FMT C (K) AFM T N (K) Ia=Li, Na,.. Ib=Cu II=Mn V=Sb,As, P > room T
Spintronics with antiferromagnets Dirac AFM IrMn I I FM AMR ~ ( m) 2 AFM Shick, Wunderlich, Jungwirth, et al., PRB 10
2. AFM-LLG equation
Phenomenology of Current Induced Dynamics in Antiferromagnets Hals et al. PRL. 106, 107206 (2011)
Dynamics of AFMs obeys the second law of Newton: Inertia motion
The non inertial mechanism requires a continuous driving force that pulls the mass over the potential barrier. A similar scenario is realized in magnetization reversal through precessional motion in ferromagnets. In contrast, in the inertial mechanism, during the action of the driving force the coordinate of the particle is hardly changed, but the particle acquires enough momentum to overcome the barrier afterwards.
3. AFM Domain Wall dynamics E. Tveten, A. Q., O. Tretiakov, A. Brataas, Phys. Rev. Lett. 110, 127208 (2013). E. Tveten, A. Q., A. Brataas, Phys. Rev. Lett. 110, 127208 (2013).
Ferromagnetic Domain Walls Neel DW Bloch DW
FM STT: current induced FM-DW motion
Spin transfer torque in magnetic textures : spin-waves induced DW motion
Racetrack Memory (IBM) S. Parkin, M. Hayashi, L. Thomas, Science 320, 190 (2008)
Staggered Dynamics in Antiferromagnets by Collective Coordinates Phys. Rev. Lett. 110, 127208 (2013)
Staggered Dynamics in Antiferromagnets by Collective Coordinates Magnetic textures are often rigid, so that only a few, soft modes dominate the magnetization dynamics. Collective Coordinates Approach
Staggered Dynamics in Antiferromagnets by Collective Coordinates Example: Texture dynamics Out of plane tilt angel and domain wall width are hard modes:
Staggered Dynamics in Antiferromagnets by Collective Coordinates Anisotropic Magneto Resistance (AMR)
Antiferromagnetic Domain Wall Motion Induced by Spin Waves In equilibrium (Walker DW): (t tan( 0, z) ) exp( ), 2 w (t 0) 0 Spin wave excitation: m 0 FM spin waves
Antiferromagnetic Domain Wall Motion Induced by Spin Waves Dynamical variables: Linearly polarized magnons:
Antiferromagnetic Domain Wall Motion Induced by Spin Waves Linear polarization
Antiferromagnetic Domain Wall Motion Induced by Spin Waves Circular polarization
Antiferromagnetic Domain Wall Motion Induced by Spin Waves Linearly polarized magnons: J mz 0 Circularly polarized magnons: Problem: Magnetic moment cannot constantly increase in an AFM! Result: Spin waves reflect from the domain wall
Antiferromagnetic Domain Wall Motion Induced by Spin Waves Circular polarization
Antiferromagnetic Spin-Orbitronics Spin Orbit Torques in Antiferromagnets Bulk inversion asymmetry Wadley et al., arxiv1503.03765v1 Wadley et al., Nat Comm. 2013 The antiferromagnetic order is Controlled by Spin orbit Torques Detected by Anisotropic Magnetoresistance