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Research Zernike (ZIAM) Physics of nanodevices Opto-Spintronics of Nanostructures

Bachelor and Master Projects

We are looking for motivated BSc and MSc students to join our group for their research projects.

Do you want to do your research project in our group? Do not hesitate to contact us to hear about open projects!

Open Research Projects (more available! contact us):

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Imaging anti-ferromagnetic domains in two-dimensional materials

Antiferromagnets are magnetic materials in which the magnetic moments order in such a way that the net magnetization is zero. They are very promising materials for ultrafast electronics and non-volatile memories working in the THz range, but the characterization of their magnetic properties is difficult due to the lack of a net magnetization. A recently discovered optical-thermolelectric microscopy technique based on the magneto-Seebeck effect makes it possible to measure magnetic structures in antiferromagnets on micrometer length scales using equipment that is readily available in most laser labs.

Focusing a laser beam onto the antiferromagnet creates a radial heat gradient giving rise to a current in the direction of the heat gradient due to the Seebeck effect. If a region is heated where the magnetic ordering changes, for example near a domain wall, the Seebeck effect is ansisotropic and will generate a net current. By measuring this signal while scanning the laser beam over the sample, the magnetic structures can be observed.

AFM Spin-Seebeck
AFM Spin-Seebeck

In this project, you will make your own devices in the cleanroom using state-of-the-art nanofabrication and characterization equipment to study two-dimensional antiferromagnetic materials. This involves using the scotch-tape technique to exfoliate materials like NiPS3, MnPS3 and FePS3, stacking the obtained flakes with other 2D materials, patterning the stack with electron beam lithography, and adding electrodes. The measurements are done in the laser lab of the Opto-Spintronics of Nanostructures group, where you have the opportunity to work with a laser setup that you can modify, expand, and automate.

Contact for more information:

Freddie Hendriks (PhD) – f.hendriks rug.nl

Marcos Guimaraes (Asst. Professor) – m.h.guimaraes rug.nl

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Micromagnetic simulations of magnonic crystals in 2D materials

As in an optical fiber, one can guide light by periodically modulating the index of refraction of a structure by stacking up layers of two different materials in an alternating way. This is a basic one-dimensional photonic crystal, and its principle is used in reading glasses, for example, as antireflection coating. These photonic crystals have a photonic band structure, similar to their electronic counterparts where atoms are placed in a periodic grid giving rise to a band structure for electrons. In general, periodic structures can result in a band structure for any kind of wave, not only for electrons or light. In a similar way one can periodically modulate the magnetic properties of a material to create a magnonic crystal. Here, only spin waves (magnons) with certain ranges of wavelengths are allowed to travel through the crystal. When the wavelength lies inside the band gap, magnons will reflect from the magnonic crystal and it can therefore be used as a magnetic mirror.

In this project, you will theoretically investigate two-dimensional magnonic crystals. You will perform micromagnetic simulations to calculate how magnons interact with periodic magnetic structures, where the goal is to optimize these structures for future experiments. These magnonic crystals can be used to make waveguides and resonant cavities for magnons, which can be used for non-volatile computation and data storage.

The micromagnetic simulations will be done using OOMMF, an object-oriented C++ program that uses a finite-difference method to solve the equations of motion for the magnetization. After you made an input file, you can run simulations right away via the graphical user interface. You are going to use experimentally obtained data as an input for your simulations and predict the behavior of these 2D magnonic crystals.

Contact for more information:

Freddie Hendriks (PhD) – f.hendriks rug.nl

Marcos Guimaraes (Asst. Professor) – m.h.guimaraes rug.nl

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Spin-Orbit Torques in 2D van der Waals Materials

More information is stored and processed today than ever before. Since the start of the information age, the demand for faster and dimensionally smaller electronics has been a constant driving force to improve our ability to imprint and manipulate more information on a smaller scale. Current magnetic RAM (M-RAM) memory devices imprint the information in the relative orientation of the magnetization of two opposing ferromagnetic layers. Such a device uses the so-called magnetic tunnel junctions (MTJ) and is illustrated in the figure below. In these devices, the magnetization of one layer is fixed while the other is free to move, allowing one to manipulate the device from a parallel (“0”) to anti-parallel (“1”) configuration. As magnetic field-based switching is considered unscalable, new and more efficient methods of manipulating the magnetization of the free layer are studied extensively. One of these methods relies on the transfer of spin angular momentum of spin currents generated by driving electrical currents in high spin-orbit coupling materials on the magnetization of a ferromagnet. When the spin-polarization of the spin current is non-collinear with the magnetization of the ferromagnet, it is able to exert a torque. These torques, termed spin-orbit torques (SOTs), can be used to switch the magnetization of the free layer from a parallel to anti-parallel configuration or vice versa by means of an electrical current.

In this project, you will study these SOTs in specific two-dimensional materials termed transition metal dichalcogenides (TMDs). You will get hands-on experience both in fabricating nanodevices as well as performing electrical measurements under a magnetic field and performing the data analysis. In order to fabricate these devices, you will use the scotch-tape method to exfoliate 2D materials and operate state-of-the-art electron-beam lithography and metal evaporation machines in a clean room environment.

An illustration of a magnetic tunnel junction in anti-parallel (left) and parallel (right) configuration.
An illustration of a magnetic tunnel junction in anti-parallel (left) and parallel (right) configuration.

Contact for more information:

Jan Hidding (PhD) – jan.hidding rug.nl

Marcos Guimaraes (Asst. Professor) – m.h.guimaraes rug.nl

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Bilayer Graphene with a Twist

Graphene, a single layer of graphite, is perhaps one of the simplest and most famous of the two-dimensional materials family. It has been recently shown that when two graphene layers are stacked on top of each other with a little twist angle between them, the resulting band structure can be drastically modified. Since the twist angle can be positive (right-handed rotation) or negative (left-handed rotation) these structures are chiral, i.e. a mirror symmetry operation takes the right into the left-handed structure.

In addition to the exciting electronic properties, such as superconductivity and correlated electronic states, these twisted bilayer graphene (tBLG) structures possess new optical properties as well due to their chirality: they absorb circularly polarized light by different amounts if the light is left- or right-handed polarized. Therefore, the chirality can be studied by performing circular dichroism measurements where one looks at the difference in reflection of right-handed and left-handed circular polarised light; the chirality of the structure would be reflected in the circular dichroism spectra.

In this project, you will get the chance to fabricate your own tBLG samples with different rotation angles. You will characterise them optically by means of circular dichroism measurements and electrically through the photocurrent in an opto-electronic device to check whether we can observe these new correlated states and their correlation with the twist angle. To fabricate these tBLG structures, you will use the scotch-tape method to exfoliate graphene and other 2D materials, and learn transfer techniques to stack the atomic layers on top of each other. To fabricate electrical devices, you will operate state-of-the-art lithography machines in the cleanroom to contact the tBLG samples with gold electrodes. Furthermore, you will get the chance to work with an optical setup provided by our group.

An illustration of a sheet of a single layer graphene (left) and a sheet of twisted bilayer graphene (right).
An illustration of a sheet of a single layer graphene (left) and a sheet of twisted bilayer graphene (right).

Contact for more information:

Jan Hidding (PhD) – jan.hidding rug.nl

Freddie Hendriks (PhD) – f.hendriks rug.nl

Marcos Guimaraes (Asst. Professor) – m.h.guimaraes rug.nl

Last modified:11 June 2020 2.14 p.m.