CONICET | Buscador de Institutos y Recursos Humanos

Spin textures and more specific magnetic domain walls (DWs) are objects that live in the hearth of magnetic materials. They can be manipulated by magnetic field and/or spin currents, and can provide many opportunities in the field of information technology, more specifically for energy efficient data storage and manipulation once they are in low dimension systems as thin films and wires or tracks. In most of the applications it is desirable to achieve small structures and move them as fast as possible. Currently, speeds of up to a few km/s have been reached in ferrimagnetic systems. [1-3] Despite the interest that the high-speed regime has attracted, in regimes that arise at lower speeds, where intrinsic pinning plays a crucial role, there is a vast variety of physical phenomena that allow us to advance in the understanding of the DW motion phenomenon.In thin magnetic films, DWs may be described as one-dimensional elastic interfaces which move in a two-dimensional disordered medium. In this context, their dynamics and morphology under the uniform driving force induced by an applied field 𝐻 may be understood by considering few key ingredients as elasticity, disorder and thermal energy. In particular, domain walls experience a depinning transition at a characteristic applied field. Remarkably, the critical exponents of this transition are universal: the numerical value of each exponent is defined by the universality class to which DW belong. In this talk, I will present results regarding the magnetic field-driven DW dynamics in ferro- and ferrimagnetic thin films with perpendicular magnetic anisotropy. Using polar magneto-optical Kerr effect microscopy, we experimentally studied the dynamics of DWs at low temperatures. We found that thermal activation is negligible below 100K in a ferrimagnetic thin film of GdFeCo, which allowed us to directly observe and characterize the depinning transition in quasi-athermal conditions. We independently determine the values of the velocity (β = 0.30 ± 0.03) and correlation length (ν = 1.3 ± 0.3) exponents of the depinning transition. The whole family of exponents characterizing the transition is deduced, providing evidence that the depinning of magnetic domain walls is better described by the quenched Edwards-Wilkinson universality class [4, 5].References[1] Caretta, L. et al. Relativistic kinematics of a magnetic soliton. Science 370, 1438 (2020)[2] Caretta, L. et al. Fast current-driven domain walls and small skyrmions in a compensated ferrimagnet. Nature Nanotech 13, 1154 (2018).[3]Kim, K. J. et al. Fast domain wall motion in the vicinity of the angular momentum compensation temperature of ferrimagnets. Nature Mater. 16, 1187 (2017).[4] Albornoz, L. J. et al. Universal critical exponents of the magnetic domain wall depinning transition,? Phys. Rev. B 104, L060404 (2021). [5] Albornoz, L. J. et al. Domain-wall roughness in GdFeCo thin films: Crossover length scales and roughness exponents. Phys. Rev. B 104, 024203 (2021).