Niclas Teichert

Trinity College Dublin | TCD · CRANN - Center for Science, Engineering and Technology

Research in functional magnetic materials often employs thin films as model systems for finding new chemical compositions with promising properties. However, the scale-up of thin films towards bulk-like structures is challenging, since the material synthesis conditions are entirely different for thin films and e.g. rapid quenching methods. As one o...

We investigated the structural, magnetic, and electrical properties of the perpendicularly magnetized Mn4-xFexGe thin films (0.3 ≤ x ≤ 1). The tetragonally distorted structure was verified for all investigated stoichiometries. High coercive fields in the range of 1.61 T to 3.64 T at room temperature were measured and showed increasing behavior with...

Strong coupling effects in magnetocaloric materials are the key factor to achieve large magnetic entropy change. Combining insights from experiments and ab initio calculations, we review relevant coupling phenomena, including atomic coupling, stress coupling and magneto‐static coupling. For the investigations on atomic coupling, we have used Heusle...

We fabricated NiFe2Ox thin films on MgAl2O4(001) by reactive dc magnetron co-sputtering varying the oxygen partial pressure. The fabrication of a material with a variable oxygen deficiency leads to controllable electrical and optical properties which are beneficial for the investigations of the transport phenomena and could, therefore, promote the...

The present study is dedicated to the influence of different substrate and buffer layer materials on the martensitic transformation in sputter deposited epitaxial shape memory Heusler alloys. For this, the magnetocaloric Heusler alloy Ni-Co-Mn-Al \cite{Teichert2015b} is grown on MgO(001), MgAl$_{2}$O$_{4}$(001), and MgO(001)/V substrates, which exh...

This chapter is addressing the physical impact of ferromagnetic Heusler entities when approaching the nanoscale, e.g. as nanoparticles or as very small grains in magnetic shape Heusler alloys, on resulting magnetic as well as microstructural properties. Based on the soft magnetic behavior of Co2FeGa and Co2FeSi as two representatives of the full He...

An austenite-martensite transition was observed in a 100-nm-thick ${\mathrm{Ni}}_{51.6}{\mathrm{Mn}}_{32.9}{\mathrm{Sn}}_{15.5}$ film by temperature-dependent resistivity and magnetization measurements, revealing a martensite starting temperature of ${M}_{S}\ensuremath{\approx}260$ K. The influence of the structural phase transition on the electron...

Combining conventional and inverse magnetocaloric materials promises to enhance solid state refrigeration. As a first step here we present epitaxial Ni–Mn–Ga/Ni–Mn–Sn bilayer films. We examine the dependence of the lateral and normal lattice constants on the deposition sequence by combining experimental and ab initio techniques. Structural properti...

In this study we report a method for the preparation of freestanding magnetocaloric thin films. Non-stoichiometric Heusler alloys Ni-Mn-Sn, Ni-Co-Mn-Sn and Ni-Co-Mn-Al are prepared via sputter deposition. A sacrificial vanadium layer is added between the substrate and the Heusler film. By means of selective wet-chemical etching the vanadium layer c...

The exchange bias effect is commonly used to shift the coercive field of a ferromagnet. This technique is crucial for the use of magnetic tunnel junctions as logic or memory devices. Therefore, an independent switching of the two ferromagnetic electrodes is necessary to guarantee a reliable readout. Here, we demonstrate that the intrinsic exchange...

The structural, magnetic, and magnetocaloric properties of epitaxial Ni-Co-Mn-Al thin films with different compositions have been studied. The films were deposited on MgO(001) substrates by co-sputtering on heated substrates. All films show a martensitic transition where the transition temperatures are strongly dependent on the composition. The str...

Heusler nanoparticles emerge as a new class of multifunctional materials. In this critical review, the latest progress in studies on Heusler nanoparticles is summarized. The authors discuss their structural and physical properties interesting for research fields such as spintronics and ferromagnetic shape memory alloys. As a young research field, t...

A thickness dependent exchange bias in the low temperature martensitic state of epitaxial Ni-Mn-Sn thin films is found. The effect can be retained down to very small thicknesses. For a Ni50Mn32Sn18 thin film, which does not undergo a martensitic transformation, no exchange bias is observed. Our results suggest that a significant interplay between f...

Epitaxial Ni-Mn-Sn thin films of 200 nm thickness were prepared by magnetron sputtering and deposited onto MgO(100) substrate. They reveal an inverse magnetocaloric effect with a martensitic phase transition around 260 K. The resulting magnetocaloric properties of these films have been determined performing magnetization measurements in the tempera...

Two sample series of Ni-Mn-Sn thin films have been prepared in order to investigate the influence of the film thickness and composition on the martensitic transition. Epitaxial thin films with thickness ranging from 10 nm to 200 nm have been deposited on heated MgO substrates by co-sputtering from elemental targets. The investigated compositions ar...

We investigate the influence of the film thickness on the martensitic transformation for the example of Ni-Mn-Sn thin films. Epitaxial films with thicknesses ranging from 100 nm down to 10 nm were deposited on MgO by co-sputtering on heated substrates. The martensitic transformation is investigated using temperature dependent x-ray diffraction, mag...