SPINTRONICS
Starting in 1992, the group makes nanostructures in the form of nanowires produced by electrodeposition. The method allows students to produce electrically contacted nanostructures on their own, within a day. The bandwidth can be as large as 10 GHz. A temperature oscillation or a gradient can be imposed by laser irradiation. The study of single magnetic nanowires layed on micro-SQUID has been so often cited that a picture of typical sample has become the emblem of the group.
The growth method allowed us to produce multilayers of Co alternating with Cu, thus allowing us to study Giant Magnetoresistance with the current forced perpendicular to the interface, that is, in the geometry of the famous Valet-Fert model. This study gave us a handle on measuring the spin diffusion length.
The group is proud to be among the first to have demonstrated the independent predictions of Luc Berger and John Slonczewski that a large enough current density must flip the magnetization of nanostructures, thanks to the spin transfer torque. Our first result concerned pushing domain walls. We then worked with spin valves. In particular, we used electrically-detected FMR (EDFMR) to study the excitation of magnetization with spin torque. We characterized also the linear response with a low frequency measurement based on the second-harmonic response of spin valve. This fundamental spintronics work is continuing, with an effort to determine the decay length of the transverse spin polarization.
In the emerging field of spin caloritronics, we were first to demonstrate that a heat current driven through a spin valve can flip the magnetization of its free layer because one can have heat-driven spin current. We showed that our thermodynamic model which describes diffusive effects can account for the magnitude of this effect. This work is continuing with the demonstration that a heat-driven spin current can modulate the ferromagnetic resonance. Also, we have found that a mere 20 K/cm temperature gradient is sufficient to change qualitatively the ferromagnetic resonance spectrum of a macroscopic YIG slab. The rationale for this effect is yet to be ascertained.
NUCLEAR MAGNETIC RESONANCE
During his early years with NMR pioneer Prof. Slichter, Ansermet developed methods to study molecules at metal surfaces. At EPFL, in collaboration with the electrochemistry specialist prof. Wieckowski (Urbana-Champaign), he demonstrated that the methods could be extended to electrode surfaces.
In 2006, LPMN engaged in a vigorous development of dynamic nuclear polarization at high field. First, so-called dissolution DNP instruments were developed. One is still in use in the laboratories of Prof. Bodenhausen (ISIC), the other is further developed and used for NMR imaging at CIBM. Second, a collaboration between CRPP, Bodenhausen and Ansermet, with strong support from EPFL, a gyrotron was designed to be used for DNP at 400 MHz proton NMR, electrons resonating at 263 GHz. The gyrotron construction was completed in 2011 and its actual performance confirmed in the course of 2012.
Lausanne enjoys a solid reputation in its expertise in DNP, thanks to the presence of several groups addressing various challenges and application of this technique. The collaboration called SDNPI is made visible and is maintained in the form of a collegial understanding which includes colleagues of PSI, also involved in DNP (for nuclear research). See http://sdnpi.epfl.ch/.
TeraHertz
Swissto12 is a startup that spun off from LPMN in 2012.
Initially, we developed sub-THz passive components for DNP. Our VNA with extenders ranging from 200 to 750 GHz allows us to detect magnetic resonance in antiferromagnets.
We organized workshops to monitor the latest developments in THz for industry.
Swissto12 is a partner of the Horizon2020 project TRANSPIRE.
