Magnetic structures and excitations in CePd2(Al,Ga)2 series: Development of the “vibron” states

M. Klicpera, M. Boehm, P. Doležal, H. Mutka, M. M. Koza, S. Rols, D. T. Adroja, I. Puente Orench, J. Rodríguez-Carvajal, and P. Javorský
Phys. Rev. B 95, 085107 – Published 3 February 2017

Abstract

CePd2Al2xGax compounds crystallizing in the tetragonal CaBe2Ge2-type structure (space group P4/nmm) and undergoing a structural phase transition to an orthorhombic structure (Cmme) at low temperatures were studied by means of neutron scattering. The amplitude-modulated magnetic structure of CePd2Al2 is described by an incommensurate propagation vector k=(δx,12+δy,0) with δx=0.06 and δy=0.04. The magnetic moments order antiferromagnetically within the ab planes stacked along the c axis and are arranged along the direction close to the orthorhombic a axis with a maximum value of 1.5(1) μB/Ce3+. CePd2Ga2 reveals a magnetic structure composed of two components: the first is described by the propagation vector k1=(12,12,0), and the second one propagates with k2=(0,12,0). The magnetic moments of both components are aligned along the same direction—the orthorhombic [100] direction—and their total amplitude varies depending on the mutual phase of magnetic moment components on each Ce site. The propagation vectors k1 and k2 describe also the magnetic structure of substituted CePd2Al2xGax compounds, except the one with x=0.1.CePd2Al1.9Ga0.1 with magnetic structure described by k and k1 stays on the border between pure CePd2Al2 and the rest of the series. Determined magnetic structures are compared with other Ce 112 compounds. Inelastic neutron scattering experiments disclosed three nondispersive magnetic excitations in the paramagnetic state of CePd2Al2, while only two crystal field (CF) excitations are expected from the splitting of ground state J=52 of the Ce3+ ion in a tetragonal/orthorhombic point symmetry. Three magnetic excitations at 1.4, 7.8, and 15.9 meV are observed in the tetragonal phase of CePd2Al2. A structural phase transition to an orthorhombic structure shifts the first excitation up to 3.7 meV, while the other two excitations remain at almost the same energy. The presence of an additional magnetic peak is discussed and described within the Thalmeier-Fulde CF-phonon coupling (i.e., magnetoelastic coupling) model generalized to the tetragonal point symmetry. The second parent compound CePd2Ga2 does not display any sign of additional magnetic excitation. The expected two CF excitations were observed. The development of magnetic excitations in the CePd2Al2xGax series is discussed and crystal field parameters determined.

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  • Received 26 February 2016
  • Revised 10 January 2017

DOI:https://doi.org/10.1103/PhysRevB.95.085107

©2017 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Klicpera1,2,*, M. Boehm2, P. Doležal1, H. Mutka2, M. M. Koza2, S. Rols2, D. T. Adroja3,4, I. Puente Orench2,5, J. Rodríguez-Carvajal2, and P. Javorský1

  • 1Charles University, Faculty of Mathematics and Physics, Department of Condensed Matter Physics, Ke Karlovu 5, 121 16 Prague 2, Czech Republic
  • 2Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042 Grenoble Cedex 9, France
  • 3ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX, United Kingdom
  • 4Highly Correlated Matter Research Group, Physics Department, University of Johannesburg, PO Box 524, Auckland Park 2006, South Africa
  • 5Instituto de Ciencia de Materiales de Aragón, CSIC, Pedro Cerbuna 12, 50009 Zaragoza, Spain

  • *mi.klicpera@seznam.cz

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Issue

Vol. 95, Iss. 8 — 15 February 2017

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