Magnetic behaviour of RRhAl (R=La, Ce, Pr, Nd and Gd) compounds

doi:10.1016/S0038-1098(00)00034-X

Solid State Communications

Volume 114, Issue 4, 24 March 2000, Pages 223-226

https://doi.org/10.1016/S0038-1098(00)00034-X Get rights and content

Abstract

Magnetization and electrical resistivity measurements have been carried out on ternary intermetallic compounds of the formula RRhAl (R=La, Ce, Pr, Nd and Gd). These compounds with R=La and Ce crystallize in the orthorhombic Pd₂(MnPd)Ge₂ type structure while those with R=Pr, Nd and Gd crystallize in the orthorhombic TiNiSi type structure, all in the space group Pnma. The compound LaRhAl exhibits superconductivity below 2.4 K while PrRhAl, NdRhAl and GdRhAl are ferromagnetically ordered with Curie temperatures of about 5, 10 and 30 K, respectively. The compound CeRhAl shows mixed valent behaviour of the Ce ions and is neither magnetically ordered nor superconducting down to 1.7 K.

Introduction

The equiatomic ternary rare earth (R) compounds of the type RTX form with many transition metals (T) and sp elements (X). These show a variety of crystal structures and exhibit many unusual magnetic and transport properties. For instance, CeRhSb (orthorhombic TiNiSi type) is a mixed valent Ce based compound which shows the formation of pseudogap that manifests in a rapid rise in resistivity at low temperatures [1]. However, CeNiAl [2] and CeIrAl [3] are also mixed valent Ce based compounds but do not show the gap formation down to 2 K. The compound LaRhSb is superconducting [4] below 2.1 K while LaIrAl is not superconducting [3] down to 1.7 K. In our laboratory, we have been carrying out a systematic investigation of the magnetic, electronic and transport properties of equiatomic ternary compounds. In this communication we present the results of such studies on RRhAl (R=La, Ce, Pr, Nd and Gd) compounds.

Section snippets

Experimental details

The RRhAl compounds with R=La, Ce, Pr, Nd and Gd were prepared by the arc melting of stoichiometric amounts of the constituent elements on a water-cooled copper hearth. The La and Ce metals were obtained from the Materials Preparation Centre, Ames Laboratory and had a purity of 99.99% with respect to other rare earth elements. The rest of the rare earths were obtained from Leico Industries, USA and had a stated purity of 99.9%. The Rh metal was procured from Arora–Matthey and was at least 99.9%

Crystal structure

Powder X-ray diffraction studies showed that all the RRhAl compounds investigated are nearly single phase materials. The RRhAl compounds with R=La and Ce crystallize in the orthorhombic Pd(Pd,Mn)Ge-type structure while those with R=Pr, Nd and Gd crystallize in the orthorhombic TiNiSi-type structure, all in the space group Pnma [5]. It is not clear as to why La and Ce compounds adopt a different structure type than the remaining RRhAl compounds. The lattice parameters obtained by us from

Conclusions

In conclusion, magnetization/magnetic susceptibility and electrical resistivity measurements have been carried out on a new series of rare earth ternary intermetallic compounds of the general formula RRhAl with R=La, Ce, Pr, Nd, and Gd. LaRhAl is found to be superconducting with a transition temperature of 2.4 K while PrRhAl, NdRhAl and GdRhAl are magnetically ordered with Curie temperatures of 4.7, 10.5, and 29.8 K, respectively. CeRhAl shows mixed valent behaviour of Ce ions but is neither

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Systematic investigations on the magnetic properties of moderate heavy Fermion CeAg<inf>0.68</inf>Si<inf>1.32</inf> alloy
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A cerium based intermetallic compound, CeAg_0.68Si_1.32, has been synthesized using arc melting technique and its magnetic, transport and thermodynamic properties have been investigated. The sample crystallizes in hexagonal-AlB₂ type CeAg_0.68Si_1.32 phase (space group: P6/mmm) with lattice parameters: a = 0.4208(2) nm; c = 0.4156(2) nm, along with a minor impurity phase. The alloy undergoes two magnetic transitions at temperatures T₁ = 8 K and T₂ = 3.3 K in a magnetic field of $B$  = 0.01 T. The former is ferromagnetic in nature and the latter corresponds to antiferromagnetic transition. In $B$ $~$ 0.1 T, antiferromagnetic coupling is broken and metamagnetic transition is witnessed. The influence of CEF is reflected in the estimated $μ_{e f f}$ and $μ_{s a t}$ which are lower than that of the theoretical value predicted for Ce³⁺ ion. The Sommerfeld coefficient( $γ$ ) is higher than the normal metals implying CeAg_0.68Si_1.32 is a moderate heavy Fermion system with complex magnetic interactions.
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Citation Excerpt :
Later Ślebarski et al. [284] reported that the heat capacity data in CeRhAl compound show a λ-type peak at 3.8 K, which suggest the AFM transition below this temperature while the magnetization measurements suggest weak FM phase. In a strong magnetic field, weak orientation of moments in GdRhAl takes place, which suggests the canted FM structure [285]. Magnetic measurements performed on RRhGa series, reveal that NdRhGa and GdRhGa are FM, TbRhGa is AFM, while CeRhGa does not show any magnetic ordering down to lowest measured temperature [70].
RTX (R = rare earths, T = 3d/4d/5d, transition metals such as Sc, Ti, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, and X = p-block elements such as Al, Ga, In, Si, Ge, Sn, As, Sb, Bi) series is a huge family of intermetallics compounds. These compounds crystallize in different crystal structures depending on the constituents. Though these compounds have been known for a long time, they came to limelight recently in view of the large magnetocaloric effect (MCE) and magnetoresistance (MR) shown by many of them. Most of these compounds crystallize in hexagonal, orthorhombic and tetragonal crystal structures. Some of them show crystal structure modification with annealing temperature; while a few of them show iso-structural transition in the paramagnetic regime. Their magnetic ordering temperatures vary from very low temperatures to temperatures well above room temperature (∼510 K). Depending on the crystal structure, they show a variety of magnetic and electrical properties. These compounds have been characterized by means of a variety of techniques/measurements such as X-ray diffraction, neutron diffraction, magnetic properties, heat capacity, magnetocaloric properties, electrical resistivity, magnetoresistance, thermoelectric power, thermal expansion, Hall effect, optical properties, XPS, Mössbauer spectroscopy, ESR, μSR, NMR, and NQR. Some amount of work on theoretical calculations on electronic structure, crystal field interaction and exchange interactions has also been reported. The interesting aspect of this series is that they show a variety of physical properties such as Kondo effect, heavy fermion behavior, spin glass state, intermediate valence, superconductivity, multiple magnetic transitions, metamagnetism, large MCE, large positive as well as negative MR, spin orbital compensation, magnetic polaronic behavior, and pseudo gap effect. Except Mn, no other transition metal in these compounds possesses considerable magnetic moments. Because of this RMnX compounds in general have high ordering temperatures. Interstitial modification using hydrogen is found to alter their crystal structures and magnetic properties considerably. RTX compounds also show interesting pressure effects on their structural and magnetic properties. In summary, these compounds show variety of physical properties over a wide range of temperatures. This review is intended to cover all the important results obtained in this family, particularly in the last few years.
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Single crystals of rare-earth vanadium triantimonides RVSb₃, with R=La–Nd, Sm and Gd–Dy are grown out of solution. The substitution of heavier rare-earths makes the orthorhombic structure contract and accompanies changes in the magnetic properties throughout the series. Characterization of RVSb₃ family was made with single-crystal X-ray diffraction, temperature and field-dependent magnetization M(T, H), heat capacity C(T) and resistivity ρ(T). All of the compounds are metallic, and all, with the exceptions of non-magnetic LaVSb₃ and ferromagnetic CeVSb₃, show features typical of antiferromagnetic order. Thermodynamic and transport measurements indicate that these materials are highly anisotropic magnetically, due to the crystal electric field splitting of the Hund's ground state, but only manifest a moderate electrical anisotropy. Given the relative scarcity of Ce-based ferromagnets, the temperature-dependent magnetization of CeVSb₃ was measured under applied hydrostatic pressure up to 10 kbar, and T_c increases at the rate of 0.14(1) K kbar⁻¹.
Properties of the GdPdX (X = Al, Si, Ga, Ge, In, Sn) intermetallics
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Ternary GdPdX (X = Al, Si, Ga, Ge, In, Sn) compounds, obtained by the induction melting, crystallize in the stable orthorhombic structure similarly to GdRhAl. The magnetic ordering temperatures of the GdPdX and GdRhAl compounds are close to 30 K. The electrical resistivity measurements of the GdPdX compounds revealed that at higher temperatures mainly phononic contribution determines the transport properties. In the lower temperature range, however, the scattering effects due to the magnetic gadolinium sublattice seem to be predominant.
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The intermetallic compound, YRhAl, has been prepared and is found to be isomorphic with RRhAl (R=Pr, Nd, Gd, Ho and Tm) compounds crystallizing in the orthorhombic TiNiSi-type structure (space group Pnma). Heat capacity and electrical resistivity measurements in the He-3 temperature range reveal that this compound is superconducting with a transition temperature, T_c, of 0.9 K. The electronic specific heat coefficient, γ, and the Debye temperature are found to be 6.1 mJ/mol K and 197 K, respectively. The specific heat jump at the superconducting transition is found to be consistent with the BCS weak-coupling limit. This combined with the earlier observation of superconductivity in LaRhAl (T_c=2.4 K) having a different structure than that of YRhAl, suggests that the underlying structure is not very crucial for the occurrence of superconductivity in RRhAl series of compounds.

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