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109th SPring-8 Seminar

Subtitle/Subject Magnetic study of the superstructure compounds (CePd3)8M (M = Al, Zn, Ge, Ga, Sn and Mn) and (LaPd3)8Mn
Period to Jan 29 , 2004
Host/Organizer JASRI/SPring-8
Format Lecture
Fields Materials Science

Date&Time: 29 Jan, 2004, 15:00 - 16:30

Speaker: Prof. Sudesh Kumar Dhar
Affiliation: Condensed Matter Physics & Materials Science Dept.,Tata Institute of Fundamental Research

  The (CePd3)8M compounds are derived from the parent CePd3. A periodic distribution of the M atoms at the interstitial body-center position in one out of every eight CePd3 unit cells results in the formation of cubic superstructure (CePd3)8M, closely related to the AuCu3-type structure of the parent CePd3. In the superstructure, while the CePd3 skeleton is periodically distorted in space, the distortion causing M atoms themselves form a regular simple-cubic sub-lattice with nearest neighbor M-M distance of ~ 8.5 Å. The consequences of the superstructure formation are i) The Ce-Ce separation, on an average, increases by 2-3 % over its value in CePd3 weakening the strength of s-f hybridization and ii) the outer-shell electrons of the M atom contribute to the conduction band leading to minor alteration in the electronic density of states at the Fermi level. Due to these changes, (CePd3)8M compounds exhibit dense Kondo lattice behavior (M =Al, Ga and In), ordering antiferromagnetically at low temperatures with the exception for M = Mn, in contrast to valence fluctuating, paramagnetic behavior of CePd3. (LaPd3)8Mn and (CePd3)8Mn are two new dilute Mn based compounds with unusually large Mn-Mn separation of ~ 8.5 Å and Mn concentration of ~ 3 at.%. At such large near neighbor distance, the direct Mn-Mn 3d overlap is practically negligible. While the Mn ions order antiferromagnetically in (LaPd3)8Mn (TN = 46 K) with the Mn ions in a 2+ valence state, a ferromagnetic transition of the Mn ions is observed in the Ce compound (Tc = 36K). Interestingly, dilution of Mn sublattice with Al even by 25 % and the substitution of Pd with Rh and Ag at ~ 8 % level in (LaPd3)8Mn changes the valence of Mn from 2+ to 3+ and the nature of magnetic ordering from antiferromagnetic to ferromagnetic in the Rh substituted alloy. The valence change indicates varying s-d hybridization. Preliminary investigations show Kondo-lattice like behaviour in the magnetic resistivity of (LaPd3)8Mn and Al diluted alloys, indicating that this may well be the first instance of a 3d-based dense Kondo lattice compound. In (CePd3)8Mn the Kondo effect due to Ce ions dominates the thermal variation of the resistivity and the Ce ions are paramagnetic at least down to 1.5 K.

Contact Address Junichiro Mizuki (PHS 3902) JASRI/SPring-8

Last modified 2006-04-08 17:01