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Search for Valence and Structural Transition in Eu Alloy in Magnetic Field

PI of Joint-use project: A. Ikeda
Host lab: Kindo Group

The 122-type intermetallic compound Eux(Co1−xNix)2P2 shows a correlation between multiple degrees of freedom in the solid resulting in various phenomena such as isostructural transition between the collapsed tetragonal (cT) and uncollapsed tetragonal (ucT) structures, 3d magnetism, and the formation of P-P dimers. To gain insights on the correlated behavior and to search for magnetic-field-induced phase transitions, we investigate the effect of high magnetic fields on the samples of x = 0.4 and 0.5. As the samples are in the Eu valence fluctuating regime, the structural phase transition from cT to ucT may be induced by the Eu valence change under the strong magnetic fields. We have performed the magnetostriction and magnetization measurements up to 60 T in the pulsed high field generated at the IMGSL in ISSP.

Figure shows the magnetic field dependence of the magnetostriction and magnetization of the sample of x = 0.4. The magnetostriction smoothly increases with increasing magnetic fields. The behavior is in good agreement with the calculated results using the inter-configurational fluctuation model that describes the Eu valence change. This indicates that magnetostriction represents the change of the Eu valence state in the compound. The magnetization curve also shows relatively good agreement with the model at high magnetic fields. In contrast, in the low-magnetic-field region below 20 T, magnetization curves do not agree with the model. The anomalies in the magnetization at around 10 and 15 T are likely attributed to the spin-flop transitions of the 3d electrons. These results indicate that the changes in the Eu valence manifest themselves in the magnetization curves at high magnetic fields, while the magnetism of the 3d electrons manifests itself in the magnetization at low magnetic fields. We conclude that the valence change occurs within the Eu valence fluctuation regime coupled with the cT structure.

The absence of the abrupt changes in the magnetostriction should indicate that the transition to ucT structure, which is firmly coupled with the divalent Eu state, does not occur within the magnetic field range of the present study. Even higher magnetic fields or pulsed magnetic fields with slower pulse durations may induce such large state changes in the present material, which is triggered by the Eu valence change under high magnetic fields. Searching for such phase transition in higher magnetic fields using the destructive magnetic field generation method in ISSP should be an interesting future work.


References
  • [1] R. Nakamura, A. Ishita, J. Nakamura, H. Ohta, Y. Haraguchi, H. Aruga Katori, H. Ishikawa, A. Matsuo, K. Kindo, M. Nohara, and A. Ikeda, Phys. Rev. B 107, 235110 (2023).
Authors
  • R. Nakamuraa, A. Ishitaa, J. Nakamuraa, H. Ohtab, Y. Haraguchic, H. Aruga Katoric, H. Ishikawa, A. Matsuo, K. Kindo, M. Noharad, and A. Ikedaa
  • aUniversity of Electro-Communications
  • bDoshisha University
  • cTokyo University of Agriculture and Technology
  • dHiroshima University