Engineering Co2MnAlxSi1−x Heusler Compounds as a Model System to Correlate Spin Polarization, Intrinsic Gilbert Damping, and Ultrafast Demagnetization

• Published in: Advanced materials (Weinheim) Vol. 32; no. 26
• Main Authors: Guillemard, Charles, Zhang, Wei, Malinowski, Gregory, de Melo, Claudia, Gorchon, Jon, Petit‐Watelot, Sebastien, Ghanbaja, Jaafar, Mangin, Stéphane, Le Fèvre, Patrick, Bertran, Francois, Andrieu, Stéphane
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01.07.2020
• Subjects: Angular momentum; Demagnetization; Electrons; Energy dissipation; Femtosecond pulses; Ferromagnetism; Gilbert damping; Heusler compounds; Magnetic damping; Magnetic materials; Magnetization; Materials science; Parameters; Polarization (spin alignment); spin polarization; spintronics; ultrafast spin dynamics
• ISSN: 0935-9648; 1521-4095
• DOI: 10.1002/adma.201908357

Engineering of magnetic materials for developing better spintronic applications relies on the control of two key parameters: the spin polarization and the Gilbert damping, responsible for the spin angular momentum dissipation. Both of them are expected to affect the ultrafast magnetization dynamics occurring on the femtosecond timescale. Here, engineered Co2MnAlxSi1‐x Heusler compounds are used to adjust the degree of spin polarization at the Fermi energy, P, from 60% to 100% and to investigate how they correlate with the damping. It is experimentally demonstrated that the damping decreases when increasing the spin polarization from 1.1 × 10−3 for Co2MnAl with 63% spin polarization to an ultralow value of 4.6 × 10−4 for the half‐metallic ferromagnet Co2MnSi. This allows the investigation of the relation between these two parameters and the ultrafast demagnetization time characterizing the loss of magnetization occurring after femtosecond laser pulse excitation. The demagnetization time is observed to be inversely proportional to 1 – P and, as a consequence, to the magnetic damping, which can be attributed to the similarity of the spin angular momentum dissipation processes responsible for these two effects. Altogether, the high‐quality Heusler compounds allow control over the band structure and therefore the channel for spin angular momentum dissipation. High‐crystalline‐quality Heusler compounds, Co2MnAlxSi1–x, are grown. Correlation between the degree of spin polarization at the Fermi energy (ranging from 60% to 100%) and the Gilbert damping (ranging from 1.1 × 10−3 to 4 × 10−4) is obtained. An inverse relationship between demagnetization time and Gilbert damping is established.