Eur. Phys. J. Special Topics 224, 997–1019 (2015)
https://doi.org/10.1140/epjst/e2015-02443-6

Review

Role of the tuning parameter at magnetic quantum phase transitions

¹ Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
² Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany
³ Jülich Centre for Neutron Science (JCNS) at Heinz Maier-Leibnitz Zentrum (MLZ), Forschungszentrum Jülich, 85747 Garching, Germany

^a e-mail: veronika.fritsch@physik.uni-augsburg.de
^b e-mail: stockert@cpfs.mpg.de
^c e-mail: hilbert.loehneysen@kit.edu

Received: 18 February 2015
Revised: 15 May 2015
Published online: 22 July 2015

Abstract

Heavy-fermion systems, with their competition between Kondo and RKKY interactions, offer a rich variety of materials that may be driven to a magnetic quantum phase transition. Quite often, a quantum critical point can be approached by chemical substitution, notably of isoelectric ligands of Ce, as in CeCu_6−xAu_x and CePd_1−xNi_xAl. While in the former we compare pressure and concentration tuning of the magnetic structure, the latter has the additional feature of geometric frustration due to the distorted kagomé sublattice of Ce atoms in the basal plane. We further present the system CeAu₂Ge₂ where minor structural differences between crystals grown from Sn or Au-Ge flux lead to pronounced differences in the magnetic structure, with several field-induced phases in samples grown from Au-Ge flux. Finally, non-isoelectronic substitution of Ti by V is studied in CeTi_1−xV_xGe₃ where CeTiGe₃ is a ferromagnet, thus allowing the study of ferromagnetic quantum criticality, a rare case for heavy-fermion systems.