Low temperature thermopower and magnetoresistance of Sc-rich CeSc1-xTixGe
Introduction
CeScGe crystallizes in the La2Sb-type tetragonal structure [1], with nearly two-dimensional Ce double layers intercalated by Sc and Ge along the axis. This compound stands out as having the highest antiferromagnetic (AFM) ordering temperature among Cerium-based magnetic systems, [2], [3], [4]. As proposed in Ref. [5] and later verified by powder neutron diffraction experiments [6], at the Néel temperature the double layers order ferromagnetically (FM) and couple AFM along the axis. Between and [5], Ce magnetic moments lie in the basal plane [6]. When cooling below , there is a canting of the moments towards the axis concomitant with a structural transition from tetragonal to triclinic of magnetostructural origin [6].
By introducing smaller Ti () in the Sc-site () the basal plane contracts, while the interlayer distance along the axis is practically preserved: these structural and electronic changes should strongly affect the magnetism. The magnetic phase diagram of the CeSc1-xTixGe alloy was reported in Ref. [5]. Both T and decrease at different rates, merging at a critical point at . At the ordering transition changes to ferromagnetic, dropping continuously down to at , the limit of the La2Sb-type structure. From this research it was concluded that in CeScGe the Ce- orbital responsible for magnetism has a local character and that a number of factors, such as an optimized RKKY interaction and a low lying crystal field excited doublet at , converge to produce the large ordering temperature.
Thermopower, , is a convenient tool to study hybridization and crystal field effects in Cerium compounds, while resistivity and magnetoresistance measurements, can provide further information on the onset and stability of the magnetically ordered state and the nature of those phases. In this work, we present first results of a combined study of Sc-rich CeSc1-xTixGe using these techniques.
Section snippets
Experimental details
Well-annealed CeSc1-xTixGe polycrystalline samples were obtained by conventional synthesis and characterization techniques, as described in Ref. [5]. The samples for electrical resistivity and Seebeck coefficient measurements were cut using a low-speed diamond saw to typical sizes of . Both zero-field and in-field measurements using a conventional four probe technique were performed with a LR700 ac resistance bridge. A zero-Lorentz force configuration was chosen for the
Results and discussion
In Fig. 1 we present the thermopower of four different samples with Ti-concentration between and . Our measurement on CeScGe confirms a previous result reported in Ref. [8] that found a sizable negative thermopower at high temperatures. Indeed, our data reaches around , a value seldom observed in magnetic Ce-compounds in this temperature range. As Ti is introduced, the room temperature absolute thermopower is strongly reduced and changes sign for , reaching
Summary
Our results on CeSc1-xTixGe show that in this system the thermopower has a reduced absolute value in comparison with other Ce-based systems. This implies a minor contribution from the state of Ce to , which seems to be a consequence of a weak coupling with conduction band states. A numerical estimation of the overall crystal-field splitting, , serves as a means to assess the validity of this scenario. Additional valuable information could come from the measurement of some
Acknowledgement
We acknowledge S. Vanrell and F. Mangussi for their assistance at an early stage of this project. This work was partially supported by Conicet through project PIP 112-2013-0100576 and SecTyP-UN Cuyo through project 06/C513.
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2020, Journal of Magnetism and Magnetic Materials