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Title: Manipulating the stability of crystallographic and magnetic sub-lattices: A first-order magnetoelastic transformation in transition metal based Laves phase

A first-order magnetoelastic transition (FOMT) is found near the triple point between ferromagnetic, antiferromagnetic and paramagnetic phases in the magneto-chemical phase diagram of (Hf1-xNbx)Fe2 Laves phase system. We show that bringing different magnetic states to the edge of stability, both as a function of the chemical composition and under the influence of external stimuli, such as temperature, pressure and magnetic field, is essential to obtain and control FOMTs. Temperature dependent X-ray diffraction experiments reveal a discontinuity in the lattice parameter a and the unit cell volume without the change in the crystal symmetry at the FOMT. Under applied pressure, the transition temperature drastically shifts downward at a remarkable rate of –122 K/GPa. It is this first-order magnetic transition that leads to a negative thermal expansion (NTE) with average ΔV/(VΔT) ≈ –15 × 10 –6 K –1 observed over a 90 K broad temperature range, which is uncommon for magnetoelastic NTE materials. Density functional theory calculations and microstructural analyses demonstrate that the unusual broadness of the FOMT originates from phase separation between ferro- and antiferromagnetic phases, which in turn is rooted in partial segregation of Hf and Nb and a peculiar microstructure. In conclusion, this new understanding of the composition-structure-property relationshipsmore » in transition metal based Laves phases is an essential step toward a better control and more precise tailoring of rich functionalities in this group of material.« less
Authors:
ORCiD logo [1] ;  [1] ; ORCiD logo [1] ;  [1] ;  [1] ;  [1] ;  [1] ; ORCiD logo [1]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
Publication Date:
Report Number(s):
IS-J-9674
Journal ID: ISSN 1359-6454; PII: S1359645418304154
Grant/Contract Number:
AC02-07CH11358
Type:
Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 154; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; Sructure-properties relationship; Magnetic properties; Magneto-elastic transformation; Negative thermal expansion; Alloys
OSTI Identifier:
1440998