De Haas-van Alphen Experiments Research Articles

CEF-scheme of a semimetal [formula omitted

We measured the magnetic susceptibility and magnetization of an antiferromagnet Ce 3Sn 7 with the orthorhombic crystal structure. The experimental data are found to be well explained on the basis of the crystalline electric field (CEF) 4f-scheme under the assumption that two Ce atoms in the 2(a) site possess a magnetic moment of 0.36 μ B / Ce and one Ce atom in the 4(i) site possesses no magnetic moment as in a valence fluctuating compound CeSn 3, which was previously proposed by Bonnet et al. Furthermore, we carried out the de Haas–van Alphen experiment. The detected Fermi surfaces are many in number but are extremely small in volume, indicating that Ce 3Sn 7 is a semimetal.

Magnetic and Fermi Surface Properties of an Antiferromagnet Ce3Sn7

We measured the electrical resistivity, specific heat, magnetic susceptibility, high-field magnetization, thermal expansion and magnetostriction of an antiferromagnet Ce 3 Sn 7 with the orthorhombic crystal structure. The experimental data are found to be well explained on the basis of the crystalline electric field (CEF) 4 f -scheme previously proposed by Bonnet et al. in which the two Ce atoms at the 2(a) site possess a magnetic moment of 0.36 µ B /Ce and the one Ce atom at the 4(i) site possesses no magnetic moment as in a valence fluctuating compound CeSn 3 . We also constructed the antiferromagnetic phase diagram for the three principal directions. Furthermore, we carried out the de Haas–van Alphen experiment. Fermi surfaces are many in number but extremely small in volumes, indicating that Ce 3 Sn 7 is a semimetal.

High Temperature Magnetic Properties of UIr Single Crystals

The discovery of a superconducting phase under pressure in the ferromagnet UGe2 1) and even at ambient pressure in URhGe has put a renewed interest on ferromagnetic compounds with a relatively small Curie temperature. U–T binary compounds (T = Ru, Rh, Ir) were previously investigated on their large variety of magnetic properties. With a Curie temperature of 46K, UIr is a natural candidate for searching exotic properties such as non-Fermi liquid behavior or superconductivity. The magnetic behavior of UIr constitutes itself an interesting subject. First, low-temperature magnetic investigations and neutron diffraction studies on polycrystalline samples indicated that this compound is a ferromagnet with an easy axis oriented along the 1⁄2010 direction. Magnetic investigations performed on single crystals revealed the easy axis parallel to 1⁄210 1 . De Haas van Alphen experiments carried out on single crystals showed evidence of moderate heavy fermion properties at low temperatures, indicating cyclotron effective masses ranging from 10 to 30m0 (m0, rest mass of an electron), in agreement with an enhanced coefficient of the electronic specific heat of about 50mJ/molK. Such characteristics are better explained in an itinerant magnetism picture. On the other hand, the strong magnetic anisotropy and the Curie–Weiss behavior observed above 500K on polycrystalline samples are pointing to a localized picture. Furthermore, studies under pressure indicated a strong suppression of TC in UIr with increasing pressures. For a better understanding of the magnetic behavior of UIr, here we report magnetic investigations performed on UIr single crystals in the temperature range from 2K to 800K. UIr single crystals were grown by the Czochralski method in a tetra-arc furnace. Magnetic measurements were performed using a SQUID magnetometer for investigations at both low and high temperatures. Above 300K we used the commercial oven option. In this temperature region the samples were fixed using Cu wires (99.9%) previously annealed up to 800K. This procedure allowed a temperature independent background. The measurements were carried out on several pieces cut from a main single crystal. This was necessary since some of the samples were found to break apart around 600K, mostly along the ð010Þ plane. The main crystallographic directions used for measurements were determined by Laue diffraction patterns. As shown in Fig. 1, UIr crystallizes in the monoclinic structure (space group P21, a 1⁄4 5:62 A, b 1⁄4 10:59 A, c 1⁄4 5:60 A and 1⁄4 98:9 ). The arrows indicate an easy axis for the magnetic moments as determined from the low temperature magnetization curves plotted in Fig. 2. We can conclude only that the easy axis is close to 1⁄210 1 , supporting the conclusion of Yamamoto et al. and in contradiction to other results. Along this direction, a saturation moment is 0.5 B. We note that the magnetization along 1⁄2010 increases linearly with increasing fields, which is compared to the previous magnetization curve containing a small ferromagnetic component. This is mainly due to the sample alignement. The anisotropy is preserved even at high temperatures, as it can be seen from the temperature dependence of the magnetization plotted in Fig. 3. Even at 800K the ratio between magnetization along the easy axis and the hard axis remains double. A plot of the reciprocal susceptibility, as shown in Fig. 4, confirms this fact. Curie–Weiss fits in the high temperature region yield effective magnetic moment values of 3.40, 3.45 and 3.85 B a b

Exotic behaviours in the Pr-based filled skutterudites

The exotic features of the Pr-based filled skutterudites are reviewedbased on the electronic transport properties, specific heat and deHaas–van Alphen experiments, putting the emphasis on PrFe4P12 andPrOs4Sb12.As references, the experiments on the related La- and Ce-filledskutterudites are also examined and discussed. Compared to their Lareference compounds, the Fermi surface is very similar in PrOs4Sb12,suggesting the well localized character of 4f electrons, while it looks largely different in PrFe4P12.For the cyclotron effective mass, both PrFe4P12 andPrOs4Sb12exhibit a strong enhancement, in reasonable agreement with the large specific heatcoefficient.

Soft x-ray energy-dependent angle-resolved photoemission study of CeIrIn5

Soft x-ray energy-dependent angle-resolved photoemission measurementsare performed on the heavy-fermion superconductor CeIrIn5 tostudy the Fermi surface (FS) and the electronic structure near the Fermi level in the ΓMZAplane. The non-dispersive band designated as the Ce 4f7/21final state is found at 280 meV along with the main body of thevalence band consisting of highly dispersive In 5p bands, which arein good qualitative agreement with the band structure calculationbased on the itinerant 4f electron model. Furthermore, we found twoelectron-like and one hole-like cylindrical FSs at the M (A) and Γ (Z)points. The Fermi momenta of the observed FSs are consistent with the de Haas–vanAlphen experiment, while they contradict the stronger anisotropy of the FS along thekzdirection predicted by the band calculation. The results suggeststronger two-dimensionality of the electronic structure of CeIrIn5and point to the need for its theoretical verification.

De Haas–van Alphen effect under pressure in URu 2Si 2

We carried out the de Haas–van Alphen experiment under pressure for a heavy fermion antiferromagnet URu 2Si 2. The detected cyclotron mass for a nearly spherical Fermi surface under pressure changes considerably, reflecting a change of the magnetic moment. The present result is, however, inconsistent with the recent phase separated proposal.

De Haas–Van Alphen experiments under extreme conditions of low temperature, high field and high pressure, for high-quality cerium and uranium compounds

When pressure is applied to cerium and uranium compounds, the magnetic ordering temperature is suppressed and becomes zero at a critical pressure P c. Around P c, non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via a de Haas–van Alphen (dHvA) experiment when pressure crosses P c. The dHvA experiment under pressure was done for the antiferromagnets CeRh 2Si 2 and CeRhIn 5, and for a ferromagnet UGe 2. We found an abrupt change of the Fermi surface for CeRh 2Si 2 and UGe2 when crossing P c, indicating a first-order like phase transition. For CeRhIn 5, the topology of the Fermi surface was unchanged, but the cyclotron mass increased steeply above 1.6 Gpa, where superconductivity sets in.

An unusual hollow cylindrical Fermi surface of a quasi-two-dimensional compound CeAgSb2

Abstract We have carried out the de Haas-van Alphen (dHvA) experiment, together with electrical resistivity, magnetic susceptibility, magnetization and specific heat experiments on a high-quality single-crystal CeAgSb2, which has a small net ferromagnetic moment of 0.4 μB per Ce atom. The bulk magnetic properties are well explained by the crystalline electric field scheme. On the other hand, large dHvA frequencies of 108 Oe, which correspond to cylindrical Fermi surfaces, were detected by the dHvA measurement for the magnetic field along the tetragonal [001] direction, indicating the quasi-two-dimensional electronic structure. The dHvA branches of CeAgSb2 are highly different from those with small dHvA frequencies of 107 Oe for the reference compounds LaAgSb2 and YAgSb2 which exhibit a semimetallic character. The dHvA results have been compared with the results of the energy band calculations. It was concluded that the 4f electron is mainly localized and that the Fermi surface of CeAgSb2 is similar to tha...

Exotic heavy-fermion state in the filled skutteruditePrFe4P12uncovered by the de Haas–van Alphen effect

We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite PrFe$_4$P$_{12}$ exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass $m^{\rm \ast}_{\rm c}=81 m_{\rm 0}$ in the high field phase (HFP), which indicates that PrFe$_4$P$_{12}$ is the first Pr-compound in which really heavy mass has been unambiguously confirmed. Also in the low field non-magnetic ordered phase (LOP), we observed the dHvA branch with $m^{\rm \ast}_{\rm c}=10 m_{0}$ that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation.

Sawtooth chemical potential oscillations in the strongly 2D organic metal κ-(BEDT-TTF) 2I 3 at high Landau level filling factors

In the strongly two-dimensional (2D) organic metal κ-(BEDT-TTF) 2I 3, sawtooth oscillations of the chemical potential μ are observed by means of Shubnikov–de Haas and de Haas–van Alphen experiments. The sawtooth shape of these oscillations of μ corresponds to the behaviour of a 2D canonical ensemble of electrons. In contrast to preceding investigations, the simple method described here probes μ directly and reveals oscillations of μ with the quantum oscillation frequency F 0=13 T.

Heavy fermions in cerium and uranium compounds studied by the de Haas–van Alphen experiment

We carried out the de Haas–van Alphen (dHvA) experiment under pressure to clarify the nature of f-electron compounds of CeRh 2Si 2, UGe 2 and CeCoIn 5. With increasing pressure, the Néel temperature T N =36 K in CeRh 2Si 2 and the Curie temperature T C =52 K in UGe 2 decrease, and a quantum critical point corresponding to the extrapolation T N or T C→0 is reached at the critical pressure p c≃1.06 and 1.52 GPa, respectively. Experimental results indicate a discontinuous change of the Fermi surface in CeRh 2Si 2 and UGe 2 when the pressure crosses p c. A heavy fermion superconductor CeCoIn 5 with a quasi-two dimensional Fermi surface was found to be located in the vicinity of the quantum critical point.

Magnetic and Fermi surface properties of UNiGa5

In order to investigate the magnetic structure and Fermi surface properties of UNiGa5, we have performed elastic neutron scattering and de Haas-van Alphen(dHvA) experiments. In the neutron scattering experiment using a single crystalline sample, we determined the antiferromagnetic propagation vector Q=(1/2,1/2,1/2) in UNiGa5. In the dHvA experiment, we observed four branches. Two branches indicate cylindrical Fermi surface and the other two branches correspond to ellipsoidal ones. The cyclotron mass was not large, ranging from 1.3 to 3.1m0.

De Haas–van Alphen effect in strongly correlated electron systems

We present the Fermi surface properties in strongly correlated electron systems of rare earth and uranium compounds via de Haas–van Alphen experiments. The conduction electrons with large cyclotron effective masses over 100m 0 (m 0 : rest mass of an electron) are detected in CeRu 2 Si 2, CeCoIn 5 and UPt 3. These electrons move slowly in the crystal. The topology of the Fermi surface and the cyclotron mass are compared to those of energy band calculations.

Three-Dimensional Reconstruction of the Fermi Surface of LaB<sub>6</sub>

The 2-dimensional angular correlations of the positron annihilation radiation (2D-ACAR) on a single crystal of LaB6 was measured for three projections. The 2D-ACAR spectra were subjected to the Van Citter-Gerhard deconvolution alghorithm. From the experimental spectra we produced the 3D k-space density rho(k) via three different methods: i) we reconstructed the 3D electron-positron momentum density rho(p) via the Cormack method. rho(k) was then obtained by applying the 3D LCW transformation to rho(p). ii) The same steps of point i) were repeated adopting a modified Fourier-transform-based algorithm. iii) The 3d k-space occupancy rho(k) was obtained directly by parameterising the Fermi surface volume with prolate ellipsoids whose axes were determined by a least-square fit to the 2D LCW transformations applied to two high symmetry projections. The ellipsoids diameters along high symmetry directions of the cubic Brillouin zone (BZ), as a fraction of the BZ size, were 0.64 (dir. X-M) and 0.82 (dir. Gamma-X). The resulting Fermi volume, as a fraction of the BZ volume, was 0.55. These results agree within 1% with those obtained via the de Haas van Alphen experiments.

Magneto-quantum oscillations in κ-(BEDT-TTF) 2Cu[N(CN) 2]Br

De Haas-van Alphen and Shubnikov-de Haas oscillations have been studied in the quasi-two-dimensional organic superconductor κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br at different magnetic field orientations with respect to the conducting layers. At ambient pressure, the oscillation frequency spectrum reflects the Fermi surface topology predicted by hand structure calculations. Estimates of the spin g-tactors indicate discrepancies either in the g values or in the conformity to the Lifshitz-Kosevich formalism of charge carriers on different parts of the Fermi surface. In contrast to the standard theory, simultaneous de Haas-van Alphen and Shuhnikov-de Haas experiments reveal a beating behavior of the magnetic breakdown oscillations in the de Haas-van Alphen but not in the Shubnikov-de Haas signal within the studied field range.

The Kondo effect to heavy fermions studied using the de Haas–van Alphen effect

In this paper, we briefly review some recent de Haas–van Alphen experiments on two contrasting types of heavy fermion/Kondo systems for varying concentrations x of the impurity ion, Ce or U. In both systems the Fermi surface is observed to vary continuously with x: in Ce x La 1− x B 6, the Ce ions behave as Kondo impurities while in U x Th 1− x Be 13 they do not. In both systems, the f electrons are also found to contribute only partially to the Fermi surface volume, therefore raising questions concerning the applicability of Fermi liquid theory.

Magnetic and Fermi Surface Properties of the Ferromagnetic Compound UGa2

We have studied the magnetic and Fermi surface properties in a ferromagnet UGa 2 . The electrical resistivity, elastic constant, thermal expansion coefficient, thermoelectric power, magnetic susceptibility and Hall coefficient indicate highly anisotropic properties, reflecting the hexagonal structure. The 5 f 2 - and 5 f 3 -CEF schemes, based on the localized 5 f -electron nature, are discussed to understand the magnetic susceptibility and magnetization data. We have also done the magnetoresistance and de Haas-van Alphen (dHvA) experiments to investigate the Fermi surface properties. Both data are very complicated, implying that the Fermi surface is a multiply-connected one. They are explained neither by the localized 5 f 2 - and 5 f 3 -core models nor by the spin-polarized 5 f -itinerant model. The cyclotron mass is, however, rather light, ranging from 0.17 to 6.2 m 0 , which is consistent with the electronic specific heat coefficient of 11 mJ/K 2 ·mol.

Cylindrical Fermi surfaces formed by a fiat magnetic Brillouin zone in uranium dipnictides

Abstract We succeeded in growing high-quality single crystals of UX2 (X = Bi, Sb, As or P) by the self-flux and chemical transport methods and carried out de Haasvan Alphen and Shubnikov-de Haas experiments. We found quasi-two-dimensional Fermi surfaces in these U compounds. Fermi surfaces of UBi2 are found to consist of one spherical Fermi surface and two cylindrical Fermi surfaces. Each Fermi surface in UBi2 changes into two cylindrical surfaces in USb2 and UAs2. This change in the Fermi surfaces is well explained on the basis of a fiat magnetic Brillouin zone. The quasi-two-dimensional character of the Fermi surfaces is mainly due to the conduction electrons in the U piane, including the 5f electrons. The itinerant nature of 5f electrons is reflected in the large cyclotron masses. The magnetic breakthrough (breakdown) phenomenon is also discussed for USb2.

Quadrupolar ordering and de Haas–van Alphen effect in UPd 3

We determined the magnetic phase diagram of UPd 3 with the hexagonal structure. There are three successive phase transitions at 7.5, 6.8 and 4.5 K. This first transition is due to the quadrupolar ordering, which was qualitatively discussed on the basis of the quadrupolar interaction with the order parameter O zx . The de Haas–van Alphen experiments were also done to clarify the Fermi surface property.

Magnetic, elastic, transport and fermi surface properties of a ferromagnetic compound UGa 2

In order to investigate the 5f electronic properties in a ferromagnet UGa 2 with the hexagonal structure, we have performed the magnetic, elastic, transport and de Haas–van Alphen experiments. From these properties, the crystal distortion is found to occur below 100 K in the basal plane, which is most likely driven by the development of a ferromagnetic moment oriented along the [1 1 2 ̄ 0] direction.