| About this Abstract |
| Meeting |
2025 TMS Annual Meeting & Exhibition
|
| Symposium
|
Neutron and X-ray Scattering in Materials Science and Engineering
|
| Presentation Title |
The Invar Effect Explained by Nuclear Resonant X-ray Scattering from Phonons and Spins |
| Author(s) |
Brent T. Fultz, Stefan Lohaus, Pedro Guzman |
| On-Site Speaker (Planned) |
Brent T. Fultz |
| Abstract Scope |
Nuclear resonant inelastic x-ray scattering (NRIXS) measures phonon spectra and nuclear forward scattering (NFS) measures magnetism of 57Fe. These NRIXS and NFS data give the vibrational entropy, Svib, and magnetic entropy, Smag, respectively. A Maxwell relationship requires that the change in entropy with pressure, ∂S/∂P, equals -∂V/∂T, which is the thermal expansion (times V). Invar, Fe64Ni36, has zero thermal expansion at 300 K.
The pressure dependences of Smag and Svib were obtained from 57Fe64Ni36 Invar in a diamond anvil cell. Magnetic disorder increases with pressure, so ∂Smag/∂P is positive. Vibrational frequencies increase with pressure, so ∂Svib/∂P is negative. These spin and phonon contributions to thermal expansion cancel precisely at pressures below 3 GPa, giving the Invar effect.
The alloy Fe55Ni45 has zero thermal expansion at pressures between 7 and 13 GPa. New data show this pressure-induced Invar effect has the same origin in a delicate balance of spins and phonons. |
| Proceedings Inclusion? |
Planned: |
| Keywords |
Magnetic Materials, Phase Transformations, |