Pressure induced Invar effect in Fe₅₅⁢Ni₄₅: An experimental study with nuclear resonant scattering

Creators: Guzman, P.¹; Lohaus, S. H.¹; Bernal-Choban, C. M.¹; Fultz, B.¹; Zhao, J. Y.; Shen, G.; Hu, M. Y.; Alp, E. E.; Lavina, B.²

1. California Institute of Technology
2. University of Chicago

Abstract

Pressure-dependent synchrotron x-ray diffraction (XRD), nuclear resonant inelastic x-ray scattering (NRIXS), and nuclear forward scattering (NFS) measurements were made on ⁵⁷Fe₅₅Ni₄₅. XRD measurements were at 298 and 392 K at pressures up to 20 GPa, confirming a pressure-induced Invar effect between 7 and 13 GPa. A decrease of the ⁵⁷Fe magnetic moment was found in NFS measurements under pressure, showing an increase in magnetic entropy. The 57Fe phonon density of states (DOS) was obtained from NRIXS measurements. The low thermal expansion in the high-pressure Invar region originates from a competition between the thermal expansion from spins and phonons as calculated from Maxwell relations. The longitudinal phonon modes changed their pressure dependence near the Curie transition, which is evidence for a spin-phonon interaction.

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Acknowledgement

This work was supported by the National Science Foundation under Grant No. 1904714 (P.G., S.H.L., C.M.B-C., and B.F.). P.G. acknowledges support of the NSF Graduate Research Fellowship DGE-1745301. This research used resources of the APS, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357 (P.G., S.H.L., C.M.B-C., and B.F.). HPCAT operations are supported by DOE-NNSA's Office of Experimental Sciences. Use of the COMPRES-GSECARS gas-loading system was supported by COMPRES under NSF Cooperative Agreement EAR 1606856 and by GSECARS through NSF Grant No. EAR-1634415 and DOE Grant No. DE-FG02-94ER14466. We thank C. Li for assistance with the pressure cells and E. Priesen Reis for assistance with magnetization measurements.

Supplemental Material

Supplementary Material includes content on the temperature dependence of the bulk modulus as a function of pressure and volume and the relation to the "Elinvar effect". Additionally, the supplementary material includes temperature dependence of the magnetization, effects of pressure on the phonon densities of states, and distributions of the hyperfine magnetic fields.

Supplemental Material

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PhysRevB.110.144419.pdf

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