C. Godart

Magnetic properties of RNi/sub 2/B/sub 2/C (R=Pr, Sm, Dy and Tb)

We report here the results of magnetization and heat capacity measurements on RNi/sub 2/B/sub 2/C (R=Pr, Sm, Dy and Tb). Sm, Dy and Th compounds order magnetically at /spl ap/10 K, 11 K and 18 K respectively. Dy and Tb compounds show field induced magnetic transitions. In the new compound, PrNi/sub 2/B/sub 2/C, magnetic susceptibility measured under zero field cooled and field cooled conditions show a significant difference.

Moment instabilities and magnetic ordering in Ce2Rh3Ge5 and Ce2Ir3Ge5

Abstract Magnetic behaviour of the four new Ce-based intermetallics, viz., Ce 2 T 3 X 5 ( T = Rh , Ir ; X = Si , Ge ) having orthorhombic U 2 Co 3 Si 5 -type structure has been studied as a function of temperature. Though Ce-ions in Ce 2 Rh 3 Si 5 are ‘trivalent’ as inferred from the cell constants, the magnetic susceptibility measurements, however, strongly suggest a nonmagnetic ground state (of Ce-ions) in this system. μ eff /Ce-ion and θ p as determined from high temperature Curie-Weiss behaviour, are 1.80μ B and 60K for Ce 2 Ir 3 Si 5 and 1.90μ B and 75K for Ce 2 Rh 3 Ge 5 . Ce 2 Ir 3 Ge 5 undergoes an antiferromagnetic ordering with T N = 10 K .

Magnetism changes in Ge and Os substituted CeRu2Si2

Abstract In Ge substituted CeRu 2 Si 2 , normal chemical pressure effects push the system from the parent heavy fermion towards antiferromagnetism to ferromagnetism. On the other hand, with Os substitution, electronic effects dominate and the system becomes less magnetic and the spin fluctuation temperature increases. This can be understood as consequences of changes in (Ce-Si) and (Ce-M) overlapping.

Magnetic properties of two new compounds: Pr/sub 2/Ni/sub 3/Si/sub 5/ and Ho/sub 2/Ni/sub 3/Si/sub 3/

Formation of two more new materials, Pr/sub 2/Ni/sub 3/Si/sub 5/ and Ho/sub 2/Ni/sub 3/Si/sub 5/, of the series, R/sub 2/Ni/sub 3/Si/sub 5/ (R=rare earth and Y) and their magnetic properties are reported here. These materials crystallize in the orthorhombic U/sub 2/Co/sub 3/Si/sub 5/-type structure (space group Ibam). Magnetic susceptibility measurement in the temperature range 5 K-300 K show that the compound Pr/sub 2/Ni/sub 3/Si/sub 5/ orders antiferromagnetically at T/sub N//spl sim/8.5 K and Ho/sub 2/Ni/sub 3/Si/sub 5/ at /spl sim/6 K. Considering T/sub N/(Gd/sub 2/Ni/sub 3/Si/sub 5/) /spl sim/15 K, T/sub N/(Pr/sub 2/Ni/sub 3/Si/sub 5/) /spl sim/ 8.5 K is rather high. The magnetic susceptibility of both of the materials, in the paramagnetic state, follows a Curie-Weiss law with effective moment close to that of the corresponding free trivalent rare earth ion. >

SPIN FLUCTUATION CHANGES IN Ge DOPED YbPd 2 Si 2

Abstract In YbPd2Si2, the valence of Yb is very close to 3+. Ge substitution of Si induces a negative pressure effect and the valence of Yb decreases. For the low Ge concentrations studied, the spin fluctuation temperature Tsf increases and χ4f, the Yb derived 4f susceptibility, obeys the scaling law χ4f(T) = F(T/Tsf).

Spin fluctuation effects in substituted CeRu2Si2 and YbPd2Si2 alloys

Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRuxSi2, CeRu2−xOsxSi2, CeRu2Si2−xGex and YbPd2Si2−xGex. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2−xGex exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd2Si2−xGex, increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2−xOsxSi2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2−xGex may be the first Ce-based heavy fermion having a magnetic ground state.

Spin Fluctuation Effects in Germanium Doped YbPd2Si2: LIII-Edge, Susceptibility and Resistivity Studies

Many ternary compounds with the general formula YbM2X2 (M = transition metal, X = Si and Ge) have been prepared and studied [1,2]. In these compounds, Yb can be 2+, 3+ or intermediate valence (IV) depending on the chemical composition of the alloy [3–5]. Intermediate valence in YbPd2Si2 was first reported using x-ray photoemission spectroscopy and LIII-edge absorption [3]. The magnetic susceptibility [6] and Mossbauer [7] measurements confirmed that Yb is IV but close to 3+ valence state. Recent results on the other IV system, CeRu2Si2, showed that the Ge substitution on the Si site creates chemical pressure effects and pushes the valence of Ce closer to 3+ [8]. The Ge substitution should lead to a decrease in the valence of Yb in YbPd2Si2. However, with small concentrations of Ge introduced in the matrix, one may except an increase in the spin fluctuation temperature, (TSF). In such a case, one should see the scaling behaviour of X4f: i.e., the Yb derived 4f susceptibility X4f(T) should scale with T/TSF as X4f∼f(T/TSF) where f is a universal function.