News

PRB on Magnetization Reversal in Ferromagnetic Nanotubes

On Thursday the 23rd, Physical Review B published our article entitled, Observation of end-vortex nucleation in individual ferromagnetic nanotubes. The paper discusses experiments in our lab that have uncovered the way in which magnetization reverses in individual ferromagnetic nanotubes (FNTs). Measurements show that reversal starts with the nucleation of magnetic vortex configurations, appearing at the FNT ends. In addition, the results reveal how magnetization reversal can be controlled by changing the FNT geometry.

To be useful as storage elements in high-density arrays, nanomagnets must reverses in a controllable, fast, and reproducible way. Near edges and surfaces, however, magnetization tends to change direction in order to minimize stray field energy. As a result, surface roughness and imperfections act as nucleation sites for magnetization reversal, resulting in variability of the switching behavior from nanomagnet to nanomagnet. The high surface-to-volume ratio inherent to small structures makes mitigating these effects essential in the design of high-density memories. Although the effect of roughness cannot be completely eliminated, one way to reduce its influence is to use structures that support flux-closure magnetization configurations, which close magnetic flux lines within the magnet. Since these configurations minimize stray field, edges and surfaces play a reduced role in reversal. FNTs support flux closure, in the form of a vortex states, in which magnetization curls around their hollow core.

The study was led by former Ph.D. student Dr. Andrea Mehlin and post-doc Dr. Boris Groß. Ph.D. student Marcus Wyss and former Masters student Thomas Schefer also contributed. The samples were provided by the groups of Prof. Dirk Grundler (EPFL) and Prof. Anna Fontcuberta i Morral (EPFL).

Davide Cadeddu Graduates

On the 13th, Ph.D. student Davide Cadeddu defended his thesis, entitled “Nanomechanics and scanning probe microscopy with nanowires”, earning his doctorate in Physics summa cum laude. The exam was chaired by Prof. Richard Warburton with Prof. Poggio and Prof. Christian Degen (ETHZ) making up the committee. Davide joined the lab in May 2013 through the SNI Ph.D. Program and was the first Ph.D. student in our lab to start working on nanowires (NWs) as scanning probe sensors. After building up a new microscope, which has now become the standard for many of our experiments, Davide started studying nonlinear mechanical effects in NWs with Dr. Floris Braakman. He later collaborated with Dr. Mathieu Munsch (Warburton Group) on several projects involving quantum dots embedded in photonic NWs. This work ultimately led to the realization of a fiber-coupled QD and the proof-of-principle demonstration of scanning electric field microscope based on an optically-addressable QD. Davide’s talent as a scientist, his collaborative spirit, and good nature, will be missed!  Congratulations to Dr. Cadeddu and good luck!

Physics II for Physicists Starts

On Thursday the 1st, the lecture “Introduction to Physics II for Physicists: Electrodynamics and Optics” began and will run until Friday, June 1st. The exam is scheduled for June 21st, 2018, 14:00 – 17:00. The lecture covers the basics of electrostatics, magnetostatics, electrodynamics, and optics. Prof. Philipp Treutlein and Prof. Poggio are sharing lecturing responsibilities.

Thibaud Ruelle in Ventura

Ph.D. student Thibaud Ruelle traveled to Ventura, California to attend the the Gordon Research Conference (GRC) on “Mechanical Systems in the Quantum Regime” from the 25th to March 2nd. The meeting brought together scientists from the areas precision sensing, metrology, quantum information processing, transduction, and fundamental physics. Participants discussed the most recent experimental and theoretical advances in mechanical systems in the quantum regime. Just as the techniques of quantum optics revolutionized the control and measurement of light, the rise of quantum acoustics now promises novel approaches to measurement science and the study of quantum physics. Thibaud presented a poster on our work coupling nanomechanical elements to a high-finesse optical cavity.

Andrea Mehlin Takes a New Job

Dr. Andrea Mehlin, who earned her Ph.D. in our group in June 2017, and has since been working as a post-doctoral researcher in the group, is starting a new job in mid-March. Andrea will be working in the research division of Innovative Sensor Technology (IST) AG in Ebnat-Kappel, Switzerland. IST AG is a leading manufacturer of physical, chemical, and biological sensors. They specializes in the development and manufacturing of temperature sensors, thermal mass flow sensors, capacitive humidity sensors, conductivity sensors, and biosensors. In addition to development and manufacturing of standard sensors, they also offer consulting and R&D tailored to specific customer requests in the field of sensor technology.

Since her first days in the lab as a Master project student, Andrea has been a crucial member of our group. She will be sorely missed. We wish her the best in her future pursuits!

Group at École de Physique des Houches

From the 11th to the 16th, members of the group attended the joint workshop Spin mechanics-5 and nanoMRI-6 at the École de Physique des Houches in Chamonix, France. The meeting brought together an interdisciplinary community of scientists focusing on a variety of topics including, nanometer-scale magnetic resonance imaging, hybrid spin mechanical systems, spintronics, optomechanics, ultrasensitive force sensing, and magnonics.

Ph.D student Nicola Rossi, post-docs Dr. Boris Groß and Dr. Floris Braakman, and Prof. Poggio attended the week-long meeting and made presentations. Nicola presented a poster entitled, “Magnetic sensing with a self-assembled nanowire”, Floris a poster entitled, “Coherent force microscopy using a nanowire mechanical resonator”, and Boris a poster entitled, “Néel-type skyrmions in multiferroic lacunar spinels – mapping out a stability phase diagram using dynamic cantilever magnetometry”. Prof. Poggio gave an invited talk entitled, “Nanomechanics and nanomagnetism” summarizing our group’s recent work.

Annual QSIT Meeting in Arosa

From the 5th to the 9th, members of the group attended the 7^th NCCR QSIT Winter School & 8^th NCCR QSIT General Meeting in Arosa, Switzerland. Ph.D students Simon Philipp, Giulio Romagnoli, and David Jaeger attended both the school and the meeting, while Ph.D. student Lorenzo Ceccarelli, post-doc Dr. Floris Braakman, and Prof. Poggio attended the meeting. Simon, David, and Floris presented posters on their work and Prof. Poggio gave a talk on the 9th entitled, “Scanning probe microscopy with Quantum Sensors”. A special thanks to Ilona Blatter for organizing an excellent meeting.

Group members at ‘Advances in Magnetics’

From the 4th to the 7th, Ph.D. student Marcus Wyss and post-doc Dr. Boris Groß attended the Advances in Magnetics (AIM) conference organized by the IEEE in La Thuile, Italy. Marcus gave a talk on the 6th entitled, “Imaging the magnetic stray field of an artificial chiral spin ice system” and Boris gave a talk on the 7th entitled, “Néel-type skyrmions in multiferroic lacunar spinels – Mapping out a stability phase diagram using dynamic cantilever magnetometry”.

Farewell Dinner

On Friday the 19th, the group held a farewell dinner for post-doc Dr. Denis Vasyukov, who will be starting a job at the Federal Institute of Metrology (METAS) in Bern in February. Denis joined the lab in February 2014, initially to work on nanowire sensors. He has since taken the lead on our scanning nano-SQUID project, establishing the fabrication and use of SQUID-on-tip sensors in our group. At the dinner, we also celebrated the first publication to come out of this project: Imaging stray magnetic field of individual ferromagnetic nanotubes. We wish Denis the best of luck in Bern and look forward to continuing to work with him on the various projects that he started here in Basel.

Two New Students Start

This month two new Ph.D. students joined our group. David Jaeger, who started with us as an intern in October 2017, officially began working as a Ph.D student on the 1st. David received his Bachelor of Science in Physics in 2014 and his Masters degree in Physics in 2017, both from the University of Basel. He did his Masters thesis in the Maletinsky group here in Basel. For his thesis he will start working on our opto-mechanics projects. Hinrich Mattiat started work as a Ph.D. student on the 15th. Hinrich received his Bachelor of Science in Interdisciplinary Sciences (Chemistry and Physics) in 2015 and his Masters degree in Interdisciplinary Sciences (Physics and Physical Chemistry) in 2017, both from the ETH Zürich. He did his Masters thesis in the Degen group at ETH Zürich. Here in Basel, he will begin working on our nanowire sensing experiments.

Scanning SQUID Paper Published

On the 2nd, our first paper on scanning nanometer-scale superconducting quantum interference device (SQUID) microscopy was published by Nano Letters as a “Just Accepted Manuscript”. This technique, originally developed by the Zeldov group at the Weizmann Institute,  allows for ultrasenitive magnetic and thermal imaging. In our latest paper, entitled, Imaging stray magnetic field of individual ferromagnetic nanotubes, we use a SQUID-on-tip (SOT) sensor to map the stray magnetic field produced by individual ferromagnetic nanotubes (FNTs) as a function of applied magnetic field. The images are taken as each FNT is led through magnetic reversal and are compared with micromagnetic simulations, which correspond to specific magnetization configurations. In magnetic fields applied perpendicular to the FNT long axis, their magnetization appears to reverse through vortex states, i.e. configurations with vortex end domains or – in the case of a sufficiently short FNT – with a single global vortex. Geometrical imperfections in the samples and the resulting distortion of idealized magnetization configurations influence the measured stray-field patterns.

The research was led by post-doc Dr. Denis Vasyukov and Ph.D. student Lorenzo Ceccarelli. Ph.D. students Marcus Wyss, Andrea Mehlin, and Nicola Rossi, and former Masters student Alexander Schwarb all worked on the project. Post-doc Dr. Boris Groß made crucial contributions in developing and running the nanomagnetic simulations required for the study. The samples were provided by the groups of Prof. Dirk Grundler (EPFL) and Prof. Anna Fontcuberta i Morral (EPFL). Important characterization measurements were done by Dr. András Kovacs (Jülich) and Dr. Reza Zamani (Lund).

MecaQ Workshop in Paris

On the 13th, Prof. Poggio participated in the 2nd annual Opto- and Nanomechanics Research Group (MecaQ) Meeting in Paris. In the afternoon, he gave a talk entitled, “Mechanical sensing of nanomagnetic systems”.

End-of-year Group Dinner

On Friday the 8th, the group held its annual end-of-year dinner. This time, the dinner was organized by Ph.D. student Marcus Wyss and was held at the Tapadera restaurant in down-town Basel. Thanks to all for a good time!

Group Members in Augsburg

On the 4th and 5th, Dr. Boris Groß and Prof. Poggio visited the Insitut für Physik at the University of Augsburg. There they were hosted by the new chair of the Experimentalphysik V division, Prof. István Kézsmárki. Ongoing collaborations were discussed and Prof. Kézsmárki gave a tour and overview of the divisions research aims. On the afternoon of the 5th, Prof. Poggio gave a talk entitled, “Nanomechanics and nanomagnetism” as part of the TRR80 Seminar series.

Block Course Underway

Our ‘Block Course’ entitled, “Measurement, Control, & Acquisition” started for students of the Nanoscience Curriculum. Dr. Floris Braakman, Dr. Boris Groß, and Ph.D. student Thibaud Ruelle, who all developed the course last year, are teaching it again this year. The course takes a look at problems in data acquisition and measurement control using modern and widely available micro-controllers.

Prof. Wolfgang Wernsdorfer in Basel

On Friday the 1st, Prof. Wolfgang Wernsdorfer from the Karlsruhe Institute of Technology (KIT) visited the department and gave the departmental Colloquium on the invitation of Prof. Poggio. His talk was entitled, “Operating quantum states in single magnetic molecules”. Before and after his talk, Prof. Wernsdorfer visited a number of research groups in the department.

Prof. Poggio at TecDay in Lugano

On the 29th, Prof. Poggio took part in the TecDay at the Liceo Cantonale di Lugano 1. The event, organized by the Swiss Academy of Engineering Sciences (SATW) aims to give high school students the chance to hear talks by researchers and others working in high-tech from both universities and industry. A wide variety of subjects are offered, especially focusing on the latest advances in natural and technical sciences. Prof. Poggio’s contribution, entitled “Nanotecnologia: come e perché”, sought to describe the growing field of nanotechnology, its goals, and its applications. More generally, the talk discussed the role that size plays in determining the behavior and function of an object. Prof. Poggio gave three 90 minute talks to a total of around 60 high school school students of all levels. A program of the TecDay can be found here.

Album Release Party

On Saturday the 25th, Ph.D. student and rock-star Marcus Wyss and his band n.eo released their first album. The release party was held at the Rockfact Music Club in Münchenstein with many group members in attendance. This photo is by Ph.D. student Alessio Campo, from the Zardo group.

Kick-off Meeting of new Sinergia Collaboration

On Thursday the 9th, our new Sinergia collaboration funded by the Swiss National Science Foundation held its kick-off meeting at EPFL. This network, entitled “Nanoskyrmionics”, is headed by Prof. Dirk Grundler (EPFL) and includes 3 other nodes, each led by a principal investigator: Dr. Jonathan White (PSI), Prof. Oleg Yazyev (EPFL), and Prof. Poggio (Basel).  The collaboration aims to do materials discovery and nanoengineering of magnetic skyrmions. From our group, Ph.D. students Simon Philipp and Giulio Romagnoli attended and gave short talks on their latest activity. Prof. Poggio was also in attendance.