Eiichi Matsuoka

Ferromagnetic Ground States with High Transition Temperatures in New Tetragonal Rare-Earth Compounds CeRu2Al2B and PrRu2Al2B

We report on the discovery of ferromagnetic ground states in the newly synthesized tetragonal compounds CeRu 2 Al 2 B and PrRu 2 Al 2 B. Polycrystalline samples of these compounds were synthesized and their magnetization M ( B ) and electrical resistivity ρ( T ) were measured as functions of the magnetic field B and the temperature T . CeRu 2 Al 2 B is a metallic compound with trivalent Ce ions and is classified into a Kondo-lattice system: a Kondo-like -ln T dependence of ρ( T ) is observed below 32 K. The cusp at T N Ce = 14.3 K and the steep increase at approximately T C Ce = 13 K observed in the magnetic susceptibility M / B ( T ) correspond to antiferromagnetic (AFM) and ferromagnetic (FM) transitions, respectively. T C Ce is the second highest transition temperature of the Ce-based ferromagnet with no other magnetic elements. PrRu 2 Al 2 B is also a metallic compound with trivalent Pr ions. The M / B ( T ) of PrRu 2 Al 2 B shows a cusp at T N Pr = 26 K and a steep increase at approximately T C Pr = ...

Sb NQR study of ferromagnetic instability in alkaline-earth-filled skutterudites SrFe4Sb12 and BaFe4Sb12

We report a 121,123 Sb nuclear quadrupole resonance (NQR) study of SrFe 4 Sb 12 and BaFe 4 Sb 12 . The absence of hyperfine splitting or marked broadening in NQR spectra even at the lowest temperature (1.5 K) suggests the absence of uniform ferromagnetic ordering in both compounds. The nuclear spin-lattice relaxation rate divided by temperature, 1/ T 1 T , does not follow the Korringa law, but shows a broad maximum at around 60 K. At temperatures higher than 80 K, 1/ T 1 T can be decomposed into two terms, (1/ T 1 T ) 0 =const. and T -dependent (1/ T 1 T ) spin . The component (1/ T 1 T ) spin is proportional to χ spin , which suggests that the present system is close to ferromagnetic instability, whereas below 60 K, (1/ T 1 T ) spin decreases to zero, being unexpected in typical nearly or weakly ferromagnetism.

Possible antiferro-octupolar order in antiferromagnetic TbB2C2 examined by Gd substitution

We have examined the effects of Gd substitution on the anomalous antiferromagnetic (AFM) properties of TbB 2 C 2 having field-induced antiferro-quadrupolar (AFQ) ordered phases. The Gd substitution induces drastic changes in the magnetic properties. The AFM structure characteristic to TbB 2 C 2 , the anomalous increase in magnetic susceptibility below T N , and the strong preference of AFM domains disappear with the substitution of low Gd content of less than 10%. We propose a promising assumption that an antiferro-octupolar (AFO) ordering occurs at T N simultaneously with AFM ordering in TbB 2 C 2 . The fragility of anomalous properties originates in the fragility of the antiferro-octupolar interaction against the substitution of Gd 3+ ions with L =0.

Reduced Thermal Conductivity and Strong Electron–Phonon Interactions in Enhanced Pauli Paramagnets AOs4Sb12 (A=Sr, Ba)

The magnetic, transport and thermal properties of alkaline-earth-filled skutterudites AOs 4 Sb 12 (A=Sr, Ba) are reported. The strong temperature dependence of the magnetic susceptibility and the moderately high value of the temperature linear coefficient of specific heat [45 mJ/(mol K 2 )] indicate the presence of a large density of states derived from Os 5 d states near the Fermi level. The lattice thermal conductivity κ ph does not show a peak near 50 K and its value is much smaller than those of the Fe- and Ru-counterparts. This unusual behavior of κ ph is attributed to the phonon scattering by localized vibrations of A 2+ ions in the oversized cage of Os 4 Sb 12 . We propose that the strong electron–phonon interaction in the presence of tunneling states is the origin for the shoulder observed in the electrical resistivity around 100 K.

Antiferroquadrupolar Ordering and Anisotropic Magnetic Phase Diagram of Dysprosium Palladium Bronze, DyPd3S4

From the measurements of magnetization and specific heat, we constructed B – T phase diagrams of single-crystalline DyPd 3 S 4 which is known to exhibit antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) ordering at low temperatures. The phase diagrams are found to be highly anisotropic and re-entrant, which are typical of rare-earth compounds exhibiting multipolar ordering. The crystalline electric field (CEF) scheme of Dy 3+ in DyPd 3 S 4 was deduced from the specific heat and magnetization measurements of the Y-diluted compounds Dy 1- x Y x Pd 3 S 4 (0.1≤ x ≤0.9) and discussed in detail. The CEF ground state was determined to be the orbitally-degenerated quartet Γ 67 (1) , and the overall splitting width was estimated to be about 104 K. No correlation was found between the anisotropy of T Q and that of the Zeeman splitting width of the ground quartet Γ 67 (1) .

Unusual Suppression of Low Energy Spin Excitations near Fermi Level in AFe4Sb12 (A=Ca, Sr, and Ba) Probed by Sb-NQR

Sb nuclear quadrupole resonances (NQR) have been performed on the alkaline-earth filled skutterudite A Fe 4 Sb 12 ( A =Ca, Sr, and Ba) being close to ferromagnetic instabiity. No hyperfine splitting in NQR spectrum even at the lowest temperature (1.5 K) confirms an absence of uniform ferromagnetic order in these compounds. Above about T * ∼70 K, the nuclear spin–lattice relaxation rate divided by temperature, 1/ T 1 T , follows an empirical relationship 1/ T 1 T = a + b χ spin with respect to the Curie Weiss (CW) like T -dependence of the static spin susceptibility χ spin . The correlation between 1/ T 1 T and χ spin is consistent with the self-consistent renormalization (SCR) theory for the three-dimensional (3D) nearly ferromagnet despite the relatively large contribution of the first term not correlating to χ spin . However, below about T * , 1/ T 1 T exhibits a gap-like suppression with a gap magnitude of about 65 K. This unusual suppression of the low energy spin excitations is contrasting to the cas...

Ising-Type Magnetic Anisotropy Derived by Γ7(1) Crystal Electric Field Ground State in Tetragonal CeRu2Al2B: 11B and 27Al NMR Studies

The magnetic properties of the new tetragonal compound CeRu 2 Al 2 B have been investigated by 11 B and 27 Al nuclear magnetic resonance (NMR) measurements. In the paramagnetic state, the Knight shift exhibits a strong Ising-type magnetic anisotropy. In the ferromagnetic order state, the ordered moment is estimated to be ≈1.8–1.85µ B /Ce from the magnitudes of the internal fields at the B and Al sites. These results strongly suggest that the Ising-like ferromagnetic ground state arises from the Γ 7 (1) ground state in CeRu 2 Al 2 B.

High Field Magnetoresistance and de Haas--van Alphen Effect in LaRu2Al10

We have measured the magnetoresistance and de Haas–van Alphen (dHvA) effect in LaRu 2 Al 10 , which is a reference compound of CeRu 2 Al 10 that exhibits an unusual transition at T 0 ≃27 K. The magnetoresistance increases with increasing magnetic field at low temperatures in the wide field directions, suggesting that LaRu 2 Al 10 is a compensated metal without an open orbit. From the dHvA experiments, about three dHvA frequency branches whose cyclotron effective masses are close to 1 m 0 ( m 0 : rest mass of an electron) were detected. The observed dHvA branches for the main Fermi surface are well explained by the results of band structure calculation based on a full potential linearized augmented-plane-wave (FLAPW) method and local-density approximation (LDA), that demonstrates the multiply connected Fermi surface with no nesting property in LaRu 2 Al 10 .

Infrared study on the electronic structure of the alkaline-earth-filled skutterudites AM4Sb12 (A=Sr, Ba; M=Fe, Ru, Os)

The optical conductivity [

A new multipolar ordering compound, rare-earth palladium bronze PrPd3S4

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