E. Z. Valiev and V. I. Bobrovskii

ON THE ABNORMAL BEHAVIOR OF COMPRESSIBILITY IN THE Fe₇₂Pt₂₈ INVAR ALLOY

In the paper, we apply our previously developed phenomenological theory of magnetoelastic interaction to a systematic description of the behavior of the elastic and magnetic characteristics of invars under pressure. This approach allows us to explain a seemingly paradoxical decrease in the compression moduli of the Fe₇₂Pt₂₈ invar under pressure alongside the simultaneously observed standard increase in the shear moduli. This paradox of compressibility in invar alloys proves to be due to two factors, namely the existence of a minimum of the compression modulus near the Curie point and the pressure-induced shift of the Curie point. Note that, in addition to a qualitative explanation of the unusual behavior of compressibility in invars, our formulas provide a good quantitative agreement with experiment. Our conclusions are supported by numerical calculations performed with the use of formulas based on the Heisenberg model with allowance made for magnetoelastic interaction.

Acknowledgment: The research was carried out at the IMP Neutron Material Science Complex under the state assignment of the Ministry of Science and Higher Education of the Russian Federation for the IMP UB RAS.

References:

1. Lohaus, S.H., Heine, M., Guzman, P., Bernal-Choban, C.M., Saunders, C.N., Shen, G., Hellman, O., Broido, D., and Fultz, B. A thermodynamic explanation of the Invar effect. Nature Physics, 2023, 19, 1642–1648. DOI: 10.1038/s41567-023-02142-z.
2. Ehn, A., Alling, B., and Abrikosov, I.A. First-principles theory of the pressure-induced Invar effect in FeNi alloys. Physical Review B, 2023, 107, 104422. DOI: 10.1103/PhysRevB.107.104422.
3. Ruban, A.V. First-principles modeling of the Invar effect in Fe₆₅Ni₃₅ by the spin-wave method. Physical Review B, 2017, 95, 174432. DOI: 10.1103/PhysRevB.95.174432.
4. Manosa, L., Saunders, G.A., Rahdi, H., Kawald, U., Pelzl, J., and Bach, H. Longitudinal acoustic mode softening and Invar behaviour in Fe₇₂Pt₂₈. Journal of Physics: Condensed Matter, 1991, 3 (14), 14, 2273–2278. DOI: 10.1088/0953-8984/3/14/006.
5. Manosa, L., Saunders, G.A., Rahdi, H., Kawald, U., Pelzl, J., and Bach, H. Acoustic-mode vibrational anharmonicity related to the anomalous thermal expansion of Invar iron alloys. Physical Review B, 1992, 45, 2224–2236. DOI: 10.1103/PhysRevB.45.2224.
6. Kim, D.J. Electron-phonon interaction mechanism of magnetovolume and magnetoelasticity effects in itinerant electron ferromagnets. Physical Review B, 1989, 39 (10), 6844–6856. DOI: 10.1103/PhysRevB.39.6844.
7. Wagner, D.V., Zverev, M., Silin, V.P., and Tkhon, M. Baric anomaly in the bulk modulus of the Invar-like alloy Fe₇₂Pt₂₈. JETP Letters, 1992, 56 (11), 595–598.
8. Valiyev, É.Z. Phenomenological theory of magnetoelastic interactions in Invars and Elinvars. Soviet Physics Uspekhi, 1991, 34 (8), 685–704. DOI: 10.1070/PU1991v034n08ABEH002463.
9. Valiev, E.Z. Problema invara. Termodinamicheskaya teoriya i analiz [The Invar Problem. Thermodynamic Theory and Analysis]. Palmarium Academic Publishing, 2017, 192 p. (In Russian).
10. Sirotin, Yu.I. and Shaskolskaya, I.P. Osnovy kristallofiziki [Fundamentals of Crystal Physics]. Nauka Publ., Мoscow, 1979, 640 p. (In Russian).
11. Valiev, E.Z. and Bobrovskii, V.I. Spontaneous volume magnetostriction in antiferromagnets and its manifestation in an FeRh alloy. Diagnostics, Resource and Mechanics of materials and structures, 2024, 5, 170–180. DOI: 10.17804/2410-9908.2024.5.170-180. Available at: http://dream-journal.org/issues/2024-5/2024-5_472.html
12. Valiev, E.Z. and Menshikov, A.Z. Linear and nonlinear magnetoelastic interactions in the molecular field theory and invar anomalies. Journal of Magnetism and Magnetic Materials, 1984, 46 (1–2), 199–206. DOI: 10.1016/0304-8853(84)90357-3.
13. Valiev, E.Z. and Kazantsev, V.A. Magnetocaloric effect in La(Fe_xSi_1−x)₁₃ ferromagnets. Journal of Experimental and Theoretical Physics, 2011, 113 (6), 1000–1005. DOI: 10.1134/S1063776111150118.

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