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

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 eff /ps and TC/T0, viz., p eff /ps ∝ (TC/T0) −3/2 . Here, ps, p eff , TC, and T0 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 TC/T0 < 1.0 in the actinide ferromagnets. However, the relation is not satisfied in a few ferromagnets with TC/T0 ∼ 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 ps increases linearly as a function of TC/T0 in the uranium and neptunium ferromagnets below (TC/T0) kink = 0.32 ± 0.02 where a kink structure appears in relation between the two quantities. ps increases more weakly above (TC/T0) kink . A possible interpretation with the TC/T0-dependence of ps is given.PACS numbers: * Phys. Rev. B. 96, 035125 (2017). † Electronic address: tateiwa.naoyuki@jaea.go.jp and conduction states. In actinide metallic compounds, the degree of localization of the 5f electrons differs in different compounds, ranging from strongly localized to itinerant character. The 3d electrons in transition metals also show various degree of localization. Differences between the 5f and 3d electrons are the smaller sensitivity to the crystal field (CF) from ligand atoms and the stronger spin-orbit coupling in the 5f s. The interplay of the spin and the unquenched orbital degrees of freedom gives rise to the peculiar features of the observed physical phenomena in actinide compounds.While many theoretical studies have been done for the role of the 5f electrons on their interesting physical properties [1][2][3], the behavior of the 5f electrons has not been fully elucidated yet. When the 5f electrons have strongly localized character at higher temperature, a Kondo-lattice picture may be appropriate for understanding the formation of the strongly correlated electric states at low temperatures as has been established in the 4f electrons system of the rare-earth cerium (Ce) and ytterbium (Yb) compounds [5][6][7]. Certainly, some actinide compounds show behaviors reminiscent of the Kondo effect such as the logarithmic temperature dependence of the electrical resistivity (ρ ∼ -lnT ). But not all physical properties in actinide compounds have been consis-

Investigation of the Itinerant Electron Ferromagnetism of Ni2+xMnGa1−x and Co2VGa Heusler Alloys

“…The other approach to obtain T A and T 0 is the analysis of the field dependence of the magnetization by means of an Arrott plot ( H/M vs. M 2 ) at the ground magnetic state, T = 5 K [7,14]. Tateiwa et al mentioned the derivation method of this approach in detail [14].…”

“…The other approach to obtain T A and T 0 is the analysis of the field dependence of the magnetization by means of an Arrott plot ( H/M vs. M 2 ) at the ground magnetic state, T = 5 K [7,14]. Tateiwa et al mentioned the derivation method of this approach in detail [14]. The magnetization in the ground state is expressed by the following equation H=F1N03(gμB)4×(−M02+M2)M where g is Lande’s g-factor; N 0 is Avogadro’s number; and F 1 is the mode–mode coupling term defined as F1=2TA215cT0 where c is equal to 1/2 and M 0 is the spontaneous magnetization.…”

“…Tateiwa et al evaluated the parameters, T A and T 0 , of actinide 5f electron systems which were analyzed by means of Equations (4)–(6) [14]. Tateiwa et al also used the units of kOe and emu/g.…”

Magnetic fluctuations in the itinerant ferromagnet LaCrGe3 studied by La139 NMR

“…The values of parameters are estimated from Ref [38]. for ZrZn2 and MnSi and Ref [40]. for UGe2, URhGe and URhAl.…”

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“…From the spontaneous magnetic moment M S and magnetization at T C , we obtained T A . Investigations into the itinerant magnetism of 3d and 5f electron systems were carried out by means of Equation ( 1) [1,[8][9][10][11][12][13]. Moreover, this theory has been applied to the ferromagnetic Heusler alloys [11,[14][15][16][17].…”