J. Pierre

Magnetic structure and crystal field in cerium compounds with CsCl-type structure

Abstract Neutron diffraction and spectroscopy experiments have been performed on the cubic (CsCl-type structure) compounds CeAg, CeZn and CeMg. CeAg orders ferromagnetically with a moment μF= 0.8μB at 1.7 K. CeZn and CeMg are antiferromagnets; at 4.2 K their magnetic moments are 1.95 μB (CeZn) and 1.85 μB (CeMg). In the ordered state, they reveal a strong quadratic distortion, the (c/a − 1) value reaching 1.9% in CeAg at 1.7 K; in CeAg additional atoms shifts seem to be present in the tetragonal cell. Crystal field parameters have been determined as |A4 〈r4〉| = 117 K (CeAg), 74 K (CeZn) and 117 K (CeMg); the consistence of the results with all the previous studies is discussed.

Magnetic and electrical properties of heusler alloys with rare earths: RInAg2

Abstract Rare earth ternary compounds RInAg2 were prepared for all rare earths except europium and ytterbium. They crystallized with a Heusler-type structure (L21). The magnetic properties and the electrical resistivity were studied in the temperature range 1.6–300 K. The paramagnetic susceptibilities showed Curie-Weiss behaviour for all the compounds except SmInAg2 which is a Van Vleck paramagnet. The asymptotic Curie temperatures θp were negative throughout the series. The cerium, neodymium, samarium, gadolinium, terbium and dysprosium compounds ordered antiferromagnetically at low temperatures, but no order was observed above 2 K in PrInAg2, HoInAg2, ErInAg2 or TmInAg2. Inelastic neutron scattering experiments were used to determine the crystal electric field parameters in the cerium, praseodymium and neodymium compounds.

Kondo lattice and heavy fermions in Heusler phases: CeInAg2−xCux

Magnetic properties, electrical resistivity, specific heat and magnetic excitations have been investigated in Heusler phases CeInAg2−xCux. The hybridization continuously increases from CeInAg2 (antiferromagnetic Kondo lattice) to CeInCu2 (heavy fermion compound). The specific heat coefficient for this last compound is found to reach 1.2 J/mole. K2 at 1.4 K, the Kondo temperature is 6 K and the Wilson ratio is close to 2.

Magnetic properties of rare earth disilicides RSi2

Abstract The magnetic properties of the rare earth disilicides (RSi 2 ) have been re-investigated. We confirm the occurrence of ferromagnetism in PrSi 2 and antiferromagnetism in GdSi 2 , TbSi 2 , DySi 2 and HoSi 2 . NdSi 2 orders at T N = 10 K and ErSi 2 orders at T c = 4.5 K. Crystal field effects are important throughout the entire series.

Magnetic interactions and crystal field in RMg3 compounds (R = Ce, Pr, Nd)

Abstract We have carried out a study of magnetic properties, electrical resistivity and of crystal field excitations using inelastic neutron scattering, in cubic RMg 3 compounds with light rare earths R = Ce, Pr and Nd. The ground states are the Γ 7 and Γ 6 doublets for CeMg 3 and NdMg 3 , which order at 3.5 and 6.5 K, respectively. PrMg 3 has the non-magnetic Γ 3 ground state and remains a Van Vleck paramagnet. The magnetic contribution to the resistivity has been separated. It allows us to evaluate the couplings between the 4f shell and the conduction band which is much larger for CeMg 3 than for the other compounds. The coupling constant Γ is negative in this case, as shown by an incipient Kondo effect in this compound.

Structural and magnetic properties of the ternary rare earth (RE) compound series REInAu2(RE~La to Lu, Y)

Abstract Results of structural, magnetic and heat capacity studies are reported for the REInAu 2 series (except europium). A crystallographic transformation from cubic to tetragonal structure occurs for the compounds with lanthanum, cerium, praseodymium and neodymium. With the exception of LaInAu 2 , the phase transition has no observable effect on the magnetic susceptibility. Compounds formed with gadolinium, terbium, dysprosium and holmium order antiferromagnetically at low temperature. In this series YbInAu 2 is confirmed to be in an unstable valence state with the maximum 2 J + 1 = 8 ground state degeneracy.

Giant magnetoresistance in sputtered and melt-spun alloys

Abstract We present an overview of our recent results on giant magnetoresistance in as-prepared and annealed heterogeneous alloys obtained by sputtering or melt-spinning. Three series of alloys have been investigated: melt-spun CoxCu(1-x), sputtered NiFexAg(1-x) and sputtered (Co70Fe30)xAg(1-x) alloys, with x between 5 and 40%.

Magnetic susceptibility, electrical resistivity and neutron spectroscopy of some cubic cerium intermetallics

Reports a study of crystal-field (CF) excitations by neutron spectroscopy and a study of magnetic susceptibility and electrical resistivity of some cubic cerium intermetallics having the CsCl or a related structure; namely the compounds CeZn, CeMg3 and CeInAg2, CeZn undergoes a first-order transition to antiferromagnetism with a strong magnetostriction at TN=30K, whereas for CeMg3 and CeInAg2 (TN=3.4 and 2.3K respectively) the transition is of second order. The magnetic resistivities of the cerium compounds obtained by subtracting the resistivities of homologous lanthanum compounds were found to decrease with increasing temperature over certain temperature ranges, indicating an incipient Kondo effect. CeMg3 has a CF splitting Delta of 195K, the ground state being the Gamma 7 doublet in contrast to the case of the CeMg compound with its Gamma 8 ground state. For CeZn and CeInAg2, the CF splitting is rather small ( Delta approximately 65 and 18K respectively).

Magnetic structures of rare earth silicides RSi2-x (R = Nd, Ho, Dy)

Abstract Magnetic structures have been determined for antiferromagnetic NdSi1.8, DySi1.75 and HoSi1.7 compounds by neutron diffraction. Except for NdSi1.8, which is a simple collinear antiferromagnet below 6 K, other structures are non-collinear. In the case of DySi1.75, we have to assume different magnitudes and tilt angles for the moments, depending on the site, which may be related to some order of silicon vacancies.

Investigation by neutron scattering of the high energy magnetic response in α-cerium and CePd3

Abstract The dynamical magnetic susceptibility has been measured in α-cerium up to energy transfers of 175 meV. The magnetic signal is small, no characteristic magnetic excitation occurs in this energy range. For CePd 3 , the magnetic response has a peak at 60 meV, which is attributed to the energy difference between magnetic and non-magnetic configurations.