Browsing by Author "Oguchi, T"

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    Helical magnetic structure in cubic chiral crystal Pr5Ru3Al2
    (International Union of Crystallography, 2017-01-01) Okuyama, D; Makino, K; Avdeev, M; Ohishi, K; Yamauchi, K; Oguchi, T; Sato, TJ
    Helical magnetic structure has recently attracted intrests because of the discovery of novel topological spin textures, forexample magnetic skyrmions and chiral magnetic soliton lattices. For such spin textures, a finite antisymmetricDzyaloshinsky–Moriya-type (cross product) interaction is crucial, activated in noncentrosymmetric crystals. Suchantisymmetric interactions have been studied mainly in 3d magnets. For example, in B20 compound (Mn,Fe,Co)Ge, theantisymmetric interaction is well investigated by the theoretical first principle calculation and found that the observed signinversion of the helicity of the helical magnetic structure by the magnetic ion substitution is quantitatively explained [1]. Incontrast, there are few studies investigating the antisymmetric interaction in 4f rare-earth based noncentrosymmetricmaterials. Murashova et al. reported the rare-earth based chiral compounds Re5Ru3Al2 with the space group I213 (Re = La,Pr) [2]. Nonetheless, their low temperature magnetism was largely unexplored. Powder Pr5Ru3Al2 was synthesized by the arc melting and high-frequency induction heating methods. The powder sampleswere annealed using muffle furnace and the high quality powder sample and single crystal were grown. In the magnetizationmeasurement using obtained Pr5Ru3Al2, the temperature dependence of the magnetic susceptibility is fitted by Curie-Weisslaw and the obtained Curie constant is close to the value for a free Pr3+ ion. At 4K, the antiferromagnetic transition isobserved [3]. To clarify the magnetic structure of Pr5Ru3Al2, we performed powder neutron diffraction using ECHIDNA inANSTO and single crystal small angle neutron scattering (SANS) using TAIKAN in J-PARC. The powder diffraction pattern at10 K is explained by the nuclear scattering of Pr5Ru3Al2. At 3 K, additional incommensurate magnetic peaks with thepropagation vector (q q q): q ~ 0.066 [r. l. u.] are observed. More noteworthy are the integrated intensities of theequivalent magnetic reflections around the nuclear 1 1 0 are not the same value. To explain the difference of the intensitiesbetween equivalent reflections, it is reasonable to conclude that the helical magnetic ordering takes place and the sign of itshelicity is determined by the sign of the crystal chirality. The magnetic structure determined by the magnetic representationand Rietveld analyses is shown in Fig. 1 (a). The composite magnetic structure obtained by adding the magnetic moments ofPr1, Pr2, Pr3, and Pr4 layers is the typical helical, as shown in Fig. 1 (b). In the SANS experiment using single crystalPr5Ru3Al2, the (q q q)-type magnetic reflection is also observed below 3.3 K. The band structure near Fermi energy iscalculated by the first principle calculation to determine the conduction band mediating RKKY interaction. From theseexperimental and theoretical results, the origin of the helical magnetic structure in Pr5Ru3Al2 will be discussed. © International Union of Crystallography
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    Small angle neutron scatterings study on the cubic chiral crystal Pr5Ru3Al2
    (International Conference on Neutron Scattering, 2017-07-12) Makino, K; Okuyama, D; Avdeev, M; Ohishi, K; Yamauchi, K; Oguchi, T; Sato, TJ
    The helical magnetic structure has attracted renewed interests because of the discovery of novel topological spin textures, for example magnetic skyrmions and chiral magnetic soliton lattices. For such spin textures, a finite antisymmetric Dzyaloshinskii-Moriya-type interaction is crucial, activated in noncentrosymmetric crystals. To date, such antisymmetric interactions have been studied mainly in 3d magnets, and few studies have been performed on 4f rare-earth (RE) magnets. Recently, Murashova et al. reported the RE-based chiral compounds RE5Ru3Al2 (RE = La, Ce, and Pr) with the space group I213. Nonetheless, their low-temperature magnetism was largely unexplored. Combining detailed magnetization and small-angle-neutron-scattering (SANS) measurements, we have scrutinized magnetic orderings in the Pr5Ru3Al2 compound at low temperatures under finite magnetic fields. In the magnetization study, we found at least four ordered phases in the ranges 1.9 < T< 3.8 K and 0 < H < 2500 Oe. The SANS study, performed using TAIKAN at J-PARC, revealed that under zero external field, two phases exists, characterized by the two distinct directions of their magnetic modulation vectors, q1 = (q q q): |q1| ~ 0.12 r. l. u. below 3.3 K, and q2 = (q q 0) : |q2| ~ |q1| observed for 3.3 K < T < 3.8 K. The magnetic modulation vectors under finite fields were similarly assigned. A first-principle electronic structure calculation has been made to understand those low-temperature ordered phases.