Single nanoparticle magnetic resonance: size and shape dependent spindynamics
Final Report Abstract
The goal of our project was to study spindynamics of magnetic nanoobjects by means of the bolometer detection and correlation of the magnetic measurements with chemical and structural properties determined by high-resolution transmission and scanning electron microscopy. Initially proposed bolometer detection based on a carbon nanotube (CNT) was found to be not suitable for the assigned tasks because of the presence of large roomtemperature noise in the measurements of the CNTs electrical resistance. Observed noise was found to be due to the electric charge fluctuations in the dielectric (Si/SiO2) or at the CNT/SiO2 interface. Its value is of the same order of magnitude as an expected CNT resistance change. To make the bolometer detection feasible, a nanoscaled Au-Pd thermocouple (ThC) device was engineered by standard electron beam lithography on a thin silicon nitride membrane to minimize heat dissipation through the substrate. In contrast with the initially proposed line sensing thermoresistive sensors (CNT-devices), thermoelectric sensors (e.g., ThCs) are based on point sensing scheme. Thus, in a ThC only a junction between two metals senses a temperature change. We fabricated the Au-Pd ThC-based bolometer as a highly sensitive sensor for probing the dissipative damping of spin dynamics in nano-sized Py stripes. The voltage responsivity and the noise equivalent power for the ThC-based bolometer are equal to 15 V/W and 3 nW Hz^-1/2, respectively. The ThC device offers a magnetic resonance response of 1 nV/ (µB W) corresponding to a sensitivity of 10^9 spins and the temperature resolution of 300 μK in vacuum. We found that such sensitivity (three orders of magnitude higher than the conventional FMR sensitivity) is only reached when using very thin thermal insulator as a substrate. The ThC-based bolometer allowed not only measurements of the temperature change of the order of a few mK due to the uniform resonant microwave absorption by the Py stripe connected to the ThC junction but also detection of standing spin waves of different mode numbers. The resonance fields of standing spin waves in the stripe depend on the stripe geometry. This was demonstrated by modifying the Py stripe using focused ion beam (FIB). A larger separation between the uniform mode and the spin wave in the spectrum of the FIB-shortened stripe was observed as compared to the spectrum of the non-modified stripe.
Publications
- “Carbon nanotube bolometer: transport properties and noise characteristics”. 2012 Solid State Phenomena 190 510-513
Irina Rod, Christian Wirtz, Olga Kazakova, Vishal Panchal, David Cox, Horst Zähres, Oliver Posth, Jürgen Lindner, Ralf Meckenstock, and Michael Farle
(See online at https://doi.org/10.4028/www.scientific.net/SSP.190.510) - “Bolometer detection of magnetic resonances in nanoscaled objects”. 2014 Nanotechnology 25 425302
Irina Rod, Ralf Meckenstock, Horst Zähres, Christian Derricks, Fedor Mushenok, Nathalie Reckers, Puchong Kijamnajsuk, Ulf Wiedwald, and Michael Farle
(See online at https://doi.org/10.1088/0957-4484/25/42/425302)
