M. Takashita

dHvA Effect Study of Metamagnetic Transition in CeRu 2Si 2 II - The State above the Metamagnetic Transition

We have performed an extensive dHvA effect study of CeRu 2 Si 2 to gain more insight into the nature of the metamagnetic transition. The angular dependence of the dHvA frequencies confirms the transition of the Fermi surfaces from those of the itinerant f electron below the metamagnetic transition field ( H m ) to those of the localized f electron above H m . The field dependence of the frequencies and effective masses are measured for all the frequencies observed with fields parallel to [001]. A waveform analysis suggests that the Fermi surfaces of the up and down spin electrons are similar in size, whereas the effective masses are significantly different. The amplitudes of the dHvA oscillations and their field dependence are anomalous above H m , implying that the dHvA oscillations above H m may possibly come from a state which is not well developed near H m .

Magnetic and Electrical Properties of UPd3

We have measured the electrical resistivity, Hall coefficient, thermoelectric power, magnetic susceptibility, magnetization, specific heat, magnetoresistance and de Haas-van Alphen (dHvA) oscillation of UPd 3 to clarify the magnetic and Fermi surface properties. A phase transition, which occurs at about 4.5 K, is most likely related to the antiferromagnetic ordering because the magnetic specific heat shows a T 3 dependence below 2 K. About ten different dHvA branches ranging from 1.8 ×10 5 Oe to 7.5 ×10 7 Oe have been observed. From the angular dependence of dHvA frequency, UPd 3 is found to consist of the closed spherical Fermi surfaces and multiply-connected ones. The cyclotron masses are light, ranging from 0.5 m 0 to 3.6 m 0 , which indicate the localized f electron character.

New features of the metamagnetic transition in CeRu2Si2 from the dHvA effect study under high pressure

We have studied the Fermi surface properties of CeRu 2 Si 2 below and above the metamagnetic transition (MT) under high pressures. The frequencies of the dHvA oscillations change considerably with pressure both below and above the MT. The pressure coefficient of the frequencies are larger than those of normal metals by more than ten times. The sign and value of the pressure coefficient depend on the dHvA frequency or the orbit. Below the MT the effective masses decrease with increasing pressure, while that above the MT is found to slightly increase. The dHvA oscillations can be traced through the MT at high pressures and it is found that the Fermi surface changes from that of the itinerant f electron to another Fermi surface which is similar to that of the localized f electron in a field range much narrower than that of the MT width in the magnetization. An analysis based on the pressure effect of the Fermi surface indicates that the Fermi surface remains unchanged when the filed approaches the MT field (...

Bulk quantum Hall effect in {eta}-Mo{sub 4}O{sub 11}

We report the observation of a bulk quantum Hall effect in the quasi-two-dimensional conductor {eta}-Mo{sub 4}O{sub 11}. The Hall resistance exhibits well-defined quantized plateaus, coincident with pronounced minima in the diagonal resistance. We propose a model involving (i) tiny quasi-two-dimensional electron and hole pockets, left over from an imperfectly nested charge-density wave, and (ii) the exchange of carriers between these mobile states and the localized charge-density-wave condensate. Together with a magnetic field, these factors result in well-separated bands of mobile states superimposed on a background continuum of localized states{emdash}the key ingredients for a quantum Hall effect. We also discuss the implications of these findings in the light of recent predictions concerning chiral metallic surface states in bulk quantum Hall systems. {copyright} {ital 1998} {ital The American Physical Society}

De Haas-van Alphen effect study of CeRu2Si2

Abstract We report an extensive study of the angular dependence of the de Haas-van Alphen frequencies for the field directions in the (0 1 0) and (0 0 1) planes, and the field dependence of the effective masses and frequencies below and above the metamagnetic transition field (Hm) in CeRu2Si2. The present study confirms our previous conclusion that the Fermi surfaces change from those of itinerant f electrons below Hm to those of localized f electons above Hm.

Magnetic properties of single crystal CeFe2Ge2

Abstract We have grown a single crystal of CeFe 2 Ge 2 by a Czochralski pulling method in a tetra-arc furnace. The electrical resistivity and magnetic susceptibility are highly anisotropic, which is similar to CeRu 2 Si 2 . The electronic specific heat coefficient is 210 mJ/K 2 mol, indicating a heavy electron system with a non-magnetic ground state. These experimental results, including the magnetoresistance, are compared to those of LaFe 2 Ge 2 .

Magnetoresistance and de Haas-van Alphen Effect in YbGa2

We have succeeded in growing a high-quality single crystal of YbGa 2 , and have done the magnetoresistance and the de Haas-van Alphen experiments. YbGa 2 is a semimetal and Fermi surfaces consist of the closed electron and hole ones. Their cyclotron masses are in the range of 0.2 to 0.9 m 0 .

De Haas-van Alphen effect of CeSb under pressure

We report a de Haas-van Alphen effect study of CeSb in the high-field ferromagnetic (F) and intermediate-field antiferromagnetic (AFF1) phases. In the F phase, the frequencies of the electron surfaces increase monotonically with pressure. On the other hand, the frequency of one particular hole surface increases with pressure, while those of the other hole surfaces decrease slightly. The effective masses of all the hole surfaces increase similarly with pressure, while those of the electron surfaces change little. In the AFF1 phase, other hole surfaces than the particular one have qualitatively different pressure dependence from that in the F phase. The frequency changes both in the F and AFF1 phases can be explained by taking the anisotropic p-f mixing model into account. However, it is difficult to understand the changes of the effective masses in terms of the f content expected for the p-f mixing model.

Fermi surface properties of ferromagnetic CeRu2Ge2

Abstract We have performed a dHvA effect study on the ferromagnetic heavy fermion compound CeRu2Ge2. Six spin-split dHvA frequency branches are observed in the (1 0 0) and (1 1 0) planes. The angular dependence of the dHvA frequencies is mostly consistent with the result reported by King and Lonzarich (KL), except that we have successfully observed the dHvA signal from a large hole surface for fields parallel to [0 0 1] and a new low-frequency branch. The effective masses measured for fields in the (0 0 1) plane agree with those of KL and do not depend on field strength. On the other hand, those for fields parallel to [0 0 1] differ considerably from those of KL and are found to decrease with increasing field. Moreover, the measured effective mass of the large hole surface is less than half of the value expected from the electronic specific heat coefficient.

De Haas-van Alphen studies of rare earth compounds

Abstract The de Haas-van Alphen amplitude of branch d in CeIn3 is reduced with oscillation by three orders of magnitude when the field is tilted from 〈100〉 to 〈110〉 in the {100} plane. This is explained by considering the angular dependence of the cyclotron mass and the electron spin g-factor.