arXiv subjects

Kazuyoshi Takeda

Publications and source records attributed to Kazuyoshi Takeda.

3 recordsLinked to original sources

arXiv2005

Specific Heat Study on a Novel Spin-Gapped System : (CH_3)_2NH_2CuCl_3

Specific heat measurements down to 120mK have been performed on a quasi-one-dimensional $S=1/2$ spin-gapped system (CH$_3$)$_2$NH$_2$CuCl$_3$ in a magnetic field up to 8 T. This compound has a characteristic magnetization curve which shows a gapless ground state and a plateau at 1/2 of the saturation value. We have observed a spontaneous antiferromagnetic ordering and a field-induced one below and above the 1/2 plateau field range, respectively. The field versus temperature phase diagram is quite unusual and completely different from those of the other quantum spin systems investigated so far. In the plateau field range, a double-structure in the specific heat is observed, reflecting the coexistence of ferromagnetic and antiferromagnetic excitations. These behaviors are discussed on the basis of a recently proposed novel quantum spin chain model consisting of weakly coupled ferromagnetic and antiferromagnetic dimers.

cond-mat.str-el↗

arXiv2005

Pressure-induced valence change in the rare earth metals:The case of Praseodymium

The rare earth metal praseodymium (Pr) transforms from the d-fcc crystal structure (Pr-III) to {$α$}-U one (Pr-IV) at 20 GPa with a large volume collapse (${\rmΔ} V/V$ = 0.16), which is associated with the valence change of the Pr ion. The two 4{\it f} electrons in the Pr ion is supposed to be itinerant in the Pr-IV phase. In order to investigate the electronic state of the phase IV, we performed the high pressure electrical resistance measurement using the diamond anvil cell up to 32 GPa. In the Pr-IV phase, the temperature dependence of the resistance shows an upward negative curvature, which is similar to the itinerant 5{\it f} electron system in actinide metals and compounds. This suggests the narrow quasiparticle band of the 4{\it f} electrons near the Fermi energy. A new phase boundary is found at $T_{0}$ in the Pr-IV phase. From the temperature and magnetic field dependences of the resistance at 26 GPa, the ground state of the Pr-IV phase is suggested to be magnetic. Several possibilities for the origin of $T_{0}$ are discussed.

cond-mat.str-el↗

arXiv2003

Non-Fermi Liquid Behavior in Dilute Quadrupolar System Pr$_{x}$La$_{1-x}$Pb$_3$ with $x$$\le$0.05

We have studied the low-temperature properties of Pr$_{x}$La$_{1-x}$Pb$_{3}$ with non-Kramers $Γ_{3}$ quadrupolar moments of the crystal-electric-field ground state, for a wide concentration range of Pr ions. For $x$$\le$0.05, the specific heat $C/T$ increases monotonically below $T$=1.5 K, which can be scaled with a characteristic temperature $T^{*}$ defined at each concentration $x$. The electrical resistivity $ρ$$(T)$ in the corresponding temperature region shows a marked decrease deviating from a Fermi-liquid behavior $ρ$$(T)$$\propto$$T^{2}$. The Kondo effect arising from the correlation between the dilute $Γ_{3}$ moments and the conduction electrons may give rise to such anomalous behavior.

cond-mat.str-el↗