H. Shida

Magnetic properties of stoichiometric Gd monopnictides

We report on the systematic magnetization measurements performed on the stoichiometric Gd monopnictides, ( = N, P, As, Sb, and Bi), at temperatures between 1.6 and 350 K in magnetic fields up to 42 T. GdN shows the ferromagnetic behaviour with a Curie temperature . The other samples order antiferromagnetically at the Neel temperatures = 15.9, 18.7, 23.4, and 25.8 K for = P, As, Sb, and Bi, respectively. A spin - flop transition is observed at low temperature for except GdN. Based on molecular field approximation, the nearest-neighbour and next-nearest-neighbour exchange constants and of are calculated using the experimental data. Comparing with Eu monochalcogenides, the other group of S-state rare-earth compounds, the absolute values of and in are anomalously large, and the ferromagnetic RKKY interactions due to semimetallic carriers are very weak. These anomalous properties are discussed with a new theoretical model developed very recently by Kasuya.

Evidence of formation of magnetic polaron states in semimetallic Gd-monopnictides

Abstract Large stoichiometric and nonstoichiometric single crystals of the gadolinium monopnictides GdX (X = P, As, Sb, Bi) have been grown for the first time by the mineralization method. Magnetic and transport properties of stoichiometric and nonstoichiometric samples are found to be very different. The weak ferromagnetism and the negative magnetoresistivity observed in nonstoichiometric samples of GdP and GdAs at low temperatures and low magnetic fields can be considered as clear evidence of the formation of trapped magnetic polaron states in gadolinium monopnictide systems.

Magnetic properties of ferromagnetic GdN

Abstract A polycrystalline GdN sample was prepared by the direct reaction of gadolinium metal and nitrogen gas at 1600°C and at a pressure of 1300 atm. We measured magnetization and the magnetic field dependence of the susceptibility and specific heat of GdN. Susceptibility and magnetization show ferromagnetic behavior for GdN with the saturation value reached at about 20 kOe. Specific heat measurements revealed a ferromagnetic transition in GdN at T c = 58 K with an additional broad peak around 20 K. Experimental results were explained with an exchange interaction mechanism.

Quadrupolar ordering in TmTe

Abstract (HT) phase diagram of the antiferro quadrupolar order in TmTe is studied from specific heat measurements under magnetic fields of H  [001] and [111], respectively. When H  [001], TQ first increases at low fields and decreases above 6 T. The phase diagram is discussed on a molecular field quadrupolar coupling model and crystalline electric field.

Gap formation in single-crystal CeRhSb

Abstract The results of measurements of magnetic susceptibility, electrical resistivity ϱ and thermopower S on CeRhSb single crystals are reported. Gap formation in a renormalized band manifests itself in a strong decrease in both χ(T) and S(T) below 20 K. The larger increase in ϱ(T) found for the less pure crystal suggests that impurities cause strong localization of residual carriers in the pseudogap. The anisottropy in χ(T) and ϱ(T) at low temperature closely resembles those in the isostructural Kondo semiconductor CeNiSn.

De Haas-van Alphen effects of PrIn3 and LaIn3

Abstract We have measured de Haas-van Alphen (dHvA) effects of PrIn 3 and LaIn 3 . In PrIn 3 some dHvA frequencies change with increasing magnetic field. It seems that this origin is related to the induced magnetic moment by the magnetic field in the singlet ground state.

Study of physical properties of Yb-monopnictides

Abstract Studies of magnetic and thermal properties have been carried out in ytterbium monopnictides YbX (X  N, P, As and Sb). Combining the new experimental results with other measurements, many thermal and magnetic properties were found to change regularly from YbAs to YbP and to YbN. This suggests the strength of magnetic exchange interaction increases and the strength of Kondo interaction (or the effect of magnetic polaron) decreases from YbAs to YbP and to YbN. YbSb is a very exceptional case.

Resistivity and Hall effect of GdSb and TmSb

Abstract GdSb and TmSb are typical ‘model’ materials in rare earth compounds. The former is an exchange interaction only sample and the latter is a CEF only sample. In order to compare the transport properties between the two samples, we have measured the Hall effect and resistivity of pure GdSb and TmSb in various fields. The CEF effect and magnetic scattering have been observed in both resistivity and Hall effect measurements for TmSb and GdSb, respectively. The mobilities of electrons and holes as well as the carrier concentration are calculated using the experimental data.

Specific heat study of the quadrupolar ordering in TmTe

Abstract We have measured the specific heat of TmTe for the magnetic field along [100] and [111] direction in the paramagnetic temperature regime above T Q = 1.7 K. The variation of the Schottky anomaly around 5 K with the magnetic fields is very difficult to be explained only from the crystal field effects or from the mean field quadrupolar interactions. The Schottky anomaly of Yb 1− x Tm x Te ( x = 0.1, 0.03) appeared at around 2 K. This differences may show the difference between the single-site Jahn-Teller effect in the diluted systems and the cooperative Jahn-Teller effect in the dense system.

Transport properties of stoichiometric and nonstoichiometric GdAs single crystals

A systematic investigation of the transport properties of GdAs single crystals is presented. We report on measurements of the electric resistivity, magnetoresistance and Hall effect performed on a stoichiometric and a nonstoichiometric sample at temperatures between 1.6 and 300 K in fields up to 10 T. The stoichiometric sample behaved as a well compensated semimetal that orders antiferromagnetically, while the nonstoichiometric sample showed some anomalies that could be explained qualitatively by the model of trapped magnetic polarons.