Novel Approaches to Magnetostructural phase transitions in Metallic systems (NAMM)

During last decades the magnetostructural phase transitions research field has been significantly highlighted in top journals in connection with magnetocalorics MC and barocalorics BC, materials of high relevance for cooling and refrigeration. 3d-transition metal pnictides, primarily with manganese as the element with particular electronic and magnetic features, are the object of this project.

About the project

Extensive earlier studies1 have shown that certain metallic systems undergo fascinating magnetostructural phase transitions. A few such compounds, for instance MnAs and ternary derivatives, are energetically at a subtle balance with respect to spin state (low versus high spin), electronic structure (localized versus itinerant), antiferro- (incommensurate variants included) or ferromagnetic, hexagonal or orthorhombically disorder, fully cation ordered or partly disordered. In this complex energy landscape first and second order magnetostructural transitions occurs, with multicritical points in relevant phase diagrams. Some such systems attracts large attention for applications in cooling and refrigeration in terms of magneto- or barocaloric (MC and BC) materials.

Figure 1. Performance parameters for a wide variety of magnetocaloric materials2. Manganese based intermetallics are one of the most promising and versatile MC materials with large entropy changes that occur close to room temperature.
 

This project aims at providing deep insight in fundamental structure – property relations, electronic structure, and nature of phase transitions that together underpin phenomena like MC and BC effects on ternary MnAs phases.

Objectives

Primary objective

New knowledge on magneto-structural phase transitions in 3d-based metallic compounds at verge of stability between spin states, types of long range magnetic order, crystallographic distortion.

In order to achieve genuine new knowledge we will

  • Benefit from our earlier research at the forefront, with due focus on superb sample quality
  • Select model systems where phenomena expectedly are particularly strong
  • Apply strong tools; a variety of synchrotron methods to study structure, disorder, electronic structure; neutron methods for 3d-element contrast and magnetism; PPMS for physical properties (T, P, H); DFT for predictions and understanding.

Secondary objectives

  • To provide new knowledge of importance for transfer into technology of calorics for refrigeration
  • Train one Ph.D. and one Postdoc
  • Strengthen national links to IFE via inverse adjunct position and international links by involving PhD students at CUTN, India, and PPMS/TEM collaboration with CRISMAT, Caen, France

Competences and Tools

The NAFUMA group at the Centre for Materials science and Nanotechnology (SMN) has excellent capabilities and expertise in synthesis, characterization and modelling. We operate the national RECX infrastructure, an MPMS, a 9 T PPMS with magnetization, resistivity, heat capacity, thermal conductivity option, insert for high pressure resistivity studies. We will benefit from a strong past experience in sample synthesis. Density-functional calculations will be carried out using codes like VASP-PAW, DMOL3 and WIEN2k and it will take a particular role, for stability, phase diagrams and electronic structure.

The Institute for Energy Technology (IFE), Kjeller, will benefit from their skills in ball-milling, as well as perform powder neutron diffractions studies (structure refinement, magnetic structure).

A battery of synchrotron radiation methods (e.g. XAS, XES, XPS, ARPES at MAX IV and X-ray powder diffraction at SNBL at ESRF) will provide the physical origin of the exciting stabilities of these compounds and describe crystal/magnetic structures at variable temperature, pressure and magnetic fields.

Financing

This project is financed by the Norwegian Research Council.

Cooperation

Institute for Energy Technology (IFE), Laboratoire de CRIStallographie et Sciences des MATèriaux (CRISMAT, France), Central University of Tamil Nadu (CUTN, India).

References

1A Zieba and H Fjellvåg et al., J. Magn. Magn. Mat., 68, 1987, pp. 115; A F Anderson and H Fjellvåg et al., J. Magn. Magn. Mat., 62, 1986, pp. 241; H Fjellvåg et al., Acta Chem. Scand.,  A39, 1985, pp. 671; A F Anderson and H Fjellvåg et al., J. Magn. Magn. Mat., 62, 1986, pp. 247

2 http://www.annualreviews.org/doi/suppl/10.1146/annurev-matsci-062910-0356/suppl_file/MR_42_Franco_SuppTable1.pdf

Published Jan. 31, 2018 3:24 PM - Last modified Jan. 31, 2018 3:24 PM