Itinerant ferromagnetism in actinide 5 f -electron systems: Phenomenological analysis with spin fluctuation theory

Naoyuki Tateiwa, Jiří Pospíšil, Yoshinori Haga, Hironori Sakai, Tatsuma D. Matsuda, and Etsuji Yamamoto

Phys. Rev. B 96, 035125 – Published 14 July 2017

ABSTRACT

We have carried out an analysis of magnetic data in 69 uranium, 7 neptunium, and 4 plutonium ferromagnets with the spin fluctuation theory developed by Takahashi [Y. Takahashi, J. Phys. Soc. Jpn. 55, 3553 (1986)]. The basic and spin fluctuation parameters of the actinide ferromagnets are determined and the applicability of the spin fluctuation theory to actinide $5f$ system has been discussed. Itinerant ferromagnets of the $3d$ transition metals and their intermetallics follow a generalized Rhodes-Wohlfarth relation between $p_{\mathrm{eff}}/p_s$ and $T_C/T_0$, viz., $p_{\mathrm{eff}}/p_s\propto {(T_C/T_0)}^{-3/2}$. Here, $p_s$, $p_{\mathrm{eff}}$, $T_C$, and $T_0$ are the spontaneous and effective magnetic moments, the Curie temperature, and the width of spin fluctuation spectrum in energy space, respectively. The same relation is satisfied for $T_C/T_0<1.0$ in the actinide ferromagnets. However, the relation is not satisfied in a few ferromagnets with $T_C/T_0\sim 1.0$ that corresponds to local moment system in the spin fluctuation theory. The deviation from the theoretical relation may be due to several other effects not included in the spin fluctuation theory such as the crystalline electric field effect on the $5f$ electrons from ligand atoms. The value of the spontaneous magnetic moment $p_s$ increases linearly as a function of $T_C/T_0$ in the uranium and neptunium ferromagnets below ${(T_C/T_0)}_{\mathrm{kink}}=0.32\pm 0.02$, where a kink structure appears in relation between the two quantities. $p_s$ increases more weakly above ${(T_C/T_0)}_{\mathrm{kink}}$. A possible interpretation with the $T_C/T_0$ dependence of $p_s$ is given.

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• Received 11 April 2017

https://sci-hub.tw/https://journals.aps.org/prb/abstract/10.1103/PhysRevB.96.035125