Magnetic and structural properties of Mn5+xGe3+y thin films as a function of substrate orientation

Magnetic and structural properties of Mn5+xGe3+y thin films as a function of substrate orientation

•The phase and orientation are independent of the Mn effusion cell temperature.•The layer is evenly covered with Mn and the TEM shows no other Mn-rich structure.•MCE shows a high ΔSm spread in a wider temperature range, relative to bulk Mn5Ge3. Mn5Ge3 thin films were grown on GaAs(111) and GaAs(001)...

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Bibliographic Details
Published in:Journal of magnetism and magnetic materials Vol. 539; p. 168325
Main Authors: Cardoso de Oliveira, R., Demaille, D., Casaretto, N., Zheng, Y.J., Marangolo, M., Mosca, D.H., Varalda, J.
Format: Journal Article
Language:English
Published: Amsterdam Elsevier B.V 01-12-2021
Elsevier BV
Elsevier
Subjects:
Condensed Matter
Diffusion cells
Germanides
High resolution electron microscopy
Magnetic properties
Magnetocaloric
Manganese compounds
Molecular beam epitaxy
Physics
Stoichiometry
Substrates
TEM
Thin films
Transmission electron microscopy
X-ray diffraction
Thin films
X-ray diffraction
Magnetocaloric
TEM
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Summary:•The phase and orientation are independent of the Mn effusion cell temperature.•The layer is evenly covered with Mn and the TEM shows no other Mn-rich structure.•MCE shows a high ΔSm spread in a wider temperature range, relative to bulk Mn5Ge3. Mn5Ge3 thin films were grown on GaAs(111) and GaAs(001) by Molecular Beam Epitaxy (MBE). The influence of stoichiometry and alloying of the samples was investigated using different Mn diffusion cell temperatures for each sample. X-ray diffraction (XRD) measurements reveal the following epitaxial relations: (001) Mn5Ge3//(111) GaAs and [110] Mn5Ge3//[2–1–1] GaAs for the sample grown on GaAs(111), and (111) Mn5Ge3//(001) GaAs and [−110] Mn5Ge3//[110] GaAs for the samples grown on GaAs(001). High-resolution transmission electron microscopy (HRTEM) results for a sample grown on GaAs(001) indicate that samples are around 70 nm thick and are composed of several grains with 2 different orientations corresponding to a 90° rotation around the [111] axis. Analyzing the Mn map with energy-filtered transmission electron microscopy (EFTEM) we observed that all the grains look very similar, indicating that they contain roughly the same amount of manganese. The magnetocaloric effect found in both family of samples is spread in a wider temperature range when compared with bulk Mn5.1Ge2.9 and the magnetic entropy change peak is higher than Si- or Sb- modified Mn5Ge3. This result makes the Mn5Ge3 a possible candidate for magnetic refrigeration while being a rare earth-free material.
ISSN:0304-8853
1873-4766
DOI:10.1016/j.jmmm.2021.168325