Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque

Martin Collet (1) , Xavier de Milly (2) , Olivier d'Allivy-Kelly (1) , Vladimir V. Naletov (3) , Rozenn Bernard (1) , Paolo Bortolotti (1) , Jamal Ben Youssef (4) , Vladislav Demidov (5) , Sergej Demokritov (5) , Jose Luis Prieto (6) , Manuel Muñoz (7) , Abdelmadjid Anane (1) , Vincent Cros (1) , G. de Loubens (2) , Olivier Klein (3)

1 Laboratoire Albert Fert (ex-UMPhy Unité mixte de physique CNRS/Thales)
2 SPEC - UMR3680 - Service de physique de l'état condensé
3 SPINTEC - SPINtronique et TEchnologie des Composants
4 LMB - Laboratoire de magnétisme de Bretagne
5 WWU - Westfälische Wilhelms-Universität Münster = University of Münster
6 Instituto de Sistemas Optoelectrónicos y Microtecnología
7 IMM - Instituto de Microelectronica de Madrid

Spin-orbit effects [1-4] have the potential of radically changing the field of spintronics by allowing transfer of spin angular momentum to a whole new class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed that by depositing Platinum (Pt, a normal metal) on top of a 1.3 μm thick Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer spin angular momentum through the interface between these two different materials. The outstanding feature was the detection of auto-oscillation of the YIG when enough dc current was passed in the Pt. This finding has created a great excitement in the community for two reasons: first, one could control electronically the damping of insulators, which can offer improved properties compared to metals, and here YIG has the lowest damping known in nature; second, the damping compensation could be achieved on very large objects, a particularly relevant point for the field of magnonics [6,7] whose aim is to use spin-waves as carriers of information. However, the degree of coherence of the observed auto-oscillations has not been addressed in ref. [5]. In this work, we emphasize the key role of quasi-degenerate spin-wave modes, which increase the threshold current. This requires to reduce both the thickness and lateral size in order to reach full damping compensation [8] , and we show clear evidence of coherent spin-orbit torque induced auto-oscillation in micron-sized YIG discs of thickness 20 nm.

Domaines: Science des matériaux [cond-mat.mtrl-sci]; Matière Condensée [cond-mat]

Martin Collet, Xavier de Milly, Olivier d'Allivy-Kelly, Vladimir V. Naletov, Rozenn Bernard, et al.. Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque. Nature Communications, 2016, 7 (10377), ⟨10.1038/ncomms10377⟩. ⟨hal-01138876⟩