Helimagnetic order in the re-entrant ferromagnet Ce2Fe15.3Mn1.7

Substitution of Mn for Fe in Ce2Fe17 strongly suppresses the ferromagnetic ground state, changing it into an antiferromagnetic one. However, a state of spontaneous magnetization is re-entered in the Ce2Fe17−xMnx compounds when the Mn content reaches x=1.3. Magnetic structures and magnetic interactions in the re-entrant ferromagnetic Ce2Fe15.3Mn1.7 compound have been studied using both microscopic (neutron powder diffraction in magnetic fields of up to 0.7T) and macroscopic (ac susceptibility and magnetization measurements under high pressures of up to 8kbar in magnetic fields of up to 5T) techniques. A spiral magnetic structure distorted by the presence of an in-plane ferromagnetic component is found below TN=182K. Enhancement of the ferromagnetic interactions leads to a steep transformation of the magnetic spiral to a magnetic structure with nonzero spontaneous magnetization below ΘT=59K. This structure is described by a distorted elliptical spiral model with an incommensurate propagation vector along the c axis. Magnetic field significantly expands the range of stability of this re-entrant ferromagnetic phase. In contrast to the magnetic field, application of pressure does not change ΘT within the achieved pressure range. It leads to a moderate reduction of the Néel temperature, dTN∕dP=−2.3K∕kbar. The preferential placement of Mn on some crystallographic sites in Ce2Fe17−xMnx and the related changes of volume and internal magnetic field will be discussed as possible reasons of the peculiar magnetic behavior of this compound.