Ultraschneller Spin-kaloritronischer Transport
Zusammenfassung der Projektergebnisse
The project investigates coupled spin and heat transport through normal metal/ferromagnetic metal multilayers and across normal metal/ferrimagnetic insulator interfaces at picosecond time scales using time-domain thermoreflectance and time-resolved magneto-optic Kerr effect measurements. The main results of the project are: • The so-called paradoxical diversity of ultrafast demagnetization can be described by a simple criterion considering heat capacities of, and coupling parameters between electrons, magnons, and phonons. The slowing down of ultrafast demagnetization of PtFeCu with temperature can be explained by the increase of magnetic heat capacity when approaching the Curie temperature. • Co/Cu multilayers exhibit a sizable spin heat valve effect for heat current perpendicular to the planes. We measure a change of the cross-plane thermal conductivity from ∼18 W m^-1 K^-1 at remanence to ∼32 W m^-1 K^-1 at saturation fields, which is consistent with predictions from the Wiedemann-Franz law. Explanation of this giant magnetothermal resistance effect requires the assumption of spin heat accumulation. • Spin heat accumulation created by heat transport through normal metal/ferromagnetic metal interfaces affects the spin-dependent Seebeck effect. This new degree of freedom not considered in prior work can be used to optimize devices that utilize the spin-dependent Seebeck effect. • Pulsed-laser excitation of Au/YIG bilayers creates temperature differences between electrons in Au and magnons in YIG of several 100 K during laser excitation. After laser-excitation, the temperature difference between electrons in Au and magnons in YIG remains of the order of 1 to 10 K for approximately 100 ps. At these time scales, we measure a nonequilibrium magnetization of the Au layer that can be explained considering an interfacial spin Seebeck effect. Comparison of model predication with measured data gives a value of 𝛼 ∼ 1×108 A m^-2 K^-1 for the product of spin mixing conductance and interfacial spin Seebeck coefficient. This work was selected as „Research Highlight“ in Nature Nanotechnology 12, 2017.
Projektbezogene Publikationen (Auswahl)
- Ultrafast demagnetization of FePt:Cu thin films and the role of magnetic heat capacity. Physical Review B 90, 224408 (2014)
Johannes Kimling, Judith Kimling, R. B. Wilson, B. Hebler, M. Albrecht, and D. G. Cahill
(Siehe online unter https://doi.org/10.1103/PhysRevB.90.224408) - Spin-dependent thermal transport perpendicular to the planes of Co/Cu multilayers. Physical Review B 91, 144405 (2015)
Johannes Kimling, R. B. Wilson, K. Rott, Judith Kimling, G. Reiss, and D. G. Cahill
(Siehe online unter https://doi.org/10.1103/PhysRevB.91.144405) - Was ist der Unterschied zwischen einem Induktionsprinzip und dem Prinzip der Gleichförmigkeit des Naturgeschehens? Aufklärung & Kritik 1/2016, 238
J. Kimling
- Picosecond Spin Seebeck Effect. Physical Review Letters 118, 057201 (2017)
J. Kimling, G.-M. Choi, J. T. Brackham, T. Matalla-Wagner, T. Huebner, T. Kuschel, F. Yang, D. G. Cahill
(Siehe online unter https://doi.org/10.1103/PhysRevLett.118.057201) - Spin diffusion induced by pulsed-laser heating and the role of spin heat accumulation. Physical Review B 95, 014402 (2017)
J. Kimling and D. G. Cahill
(Siehe online unter https://doi.org/10.1103/PhysRevB.95.014402) - Was ist der Unterschied zwischen einer metaphysischen Vermutung und einer methodologischen Voraussetzung? Aufklärung & Kritik 1/2017, 221
J. Kimling
