Nanostructures

Magnetism of dots and antidots prepared by nanosphere lithography

Large area, highly ordered arrays of magnetic dots and antidotswere produced by nanospherelithography [Nanotechnology 26 (2015) 425301]. The magnetic nanostructures have been fabricated by depositing Co/Pd multilayers on polystyrene masks. Change of the preparation conditions allowed to obtain both arrays of separated magnetic islands as well as arrays of antidots with adjustable sizes down to 30 nm and periods from 200 nm to 800 nm. This allowed to observe the transition between two different magnetization reversal mechanisms appearing on the border between dot and antidot regime. The studies was for the first time performed for patterned system with perpendicular magnetic anisotropy, highly ordered on a large area, where both dots and antidots were created by the same method. We have shown that the coercivity values reach a maximum for the array of antidots with a separation length close to the domain wall width. In this case, each area between three adjacent holes corresponds to a single domain configuration, which can be switched individually (Figure). On the contrary, small hole sizes and large volume of material between them results in domain wall propagation throughout the system accompanied by strong domain wall pinning at the holes.

 

Sequential reversal of individual domains in array of antidots with period of 438 nm (a-c) and domain wall propagation for 320 nm dots with period of 438 nm (d-f) using a conventional recording head. The green circles mark the single domains switched one after another (the experiment made with Scanning Magnetoresistive Microscope at the University of Augsburg in the frame of DAAD-MNiSW cooperation).

Magnetoresistive Bi sensors in nanomembrane of anodic alumina

The basic research are complemented with applied studies of nanostructured sensors. The metallic bismuth due to its high conduction electron mobility is a very good candidate as a thin film magnetoresistive sensor of magnetic field. However, it is necessary to anneal the films to get a good signal-to-noise ratio. Annealing at elevated temperatures  leads to the dewetting process, creation of Bi islands on the film surface, and loss of film continuity. In order to avoid this problems Bi was deposited by vapor deposition in the nanomembranes of anodic alumina. The matrix of metallic nanowires embedded in alumina was then annealed, showing at room temperature magnetoresistance value of 35% at 1.5 T,approximately 2 times larger  than for flat films

 

Scanning electron microscope image of (a) anodized alumina template, and (b) template filled with Bi nanowires. The plot (c) shows the magnetoresistance measured at room temperature along the nanowire direction, and perpendicularly to the nanowire axes.

 

Flexible magnetic field sensors integrated with strain gauge

The main goal is to produce flexible sensors of magnetic field and deformation basing on Giant Magnetoresistance(Co/Cu multilayers) and Anisotropic Magnetoresistance (Bi films) effects with Direct Laser Interference Lithography. The second aim of the project is to construct non-contact, optical measurement system for reading the strain on the sensor surface. The final product will be flexible magnetic field sensor integrated with deformation sensor.

Flexible magnetic field sensors fabricated in our laboratory.

Project (LIDER/008/177/L-5/NCBR/2014) supported by the:

 

Electrodeposited nanowires

Our research are focused on an investigation of the structural and magnetic properties of cobalt and iron, CoCu, FeCu, FeCr, CoFe alloy nanowires and multilayered Co/Cu, Fe/Cu and Fe/Cr nanowires prepared by electrodeposition method. The aim of investigations is to optimise themorphology, and electrodeposition parameters leading to the achievement of nanoobjects showing a desired magnetic properties (for instance: anisotropy with an easy axis of magnetization along the nanowire, the high values of coercivity and squareness of the hysteresis loop, high value of giant magnetoresistance).

 

SEM images of (a) polycarbonate membrane with pore diameter of 100 nm; (b) “flower” of CoCu overdeposited nanowires with pore diameter of 50 nm; (c) Fe nanowires with diameter of 100 nm after membrane dissolving 

 

 

Mesoporous silica

Our research focuses on the synthesis and characterization of novel functional materials based on ordered mesoporous silica. The mesoporous silica matrix functionalized by metal ions or molecular magnets (e.g. Mn12-ac) is a useful starting material for many applications. Very promising application area for these materials is information technology. Our research aims to obtain material suitable for high-density data storage or converting units in molecular Hopfield-type neurons. In this case, silica thin films with hexagonally arranged cylindrical pores oriented perpendicularly to substrate's surface are used. Taking into consideration film structure it is possible to obtain a memory cell with a diameter from 5 to 8 nm. It gives up to 4×1010 bits in 1 mm2 of the film.

 

Mesoporous silica thin film with a two-dimensional (2D) hexagonal structure ( TEM image) and  scheme of functionalization with Mn12  single-molecule magnets.