Magnetism and magnetic structures of PrMn₂Ge_2−xSi_x

Abstract

The structural and magnetic properties of seven PrMn2Ge2-xSix compounds with Si concentrations in the range x = 0.0-2.0 have been investigated by x-ray diffraction, magnetic (5-350 K), differential scanning calorimetry (300-500 K) and neutron diffraction (3-480 K) measurements. Replacement of Ge by Si leads to a contraction of the unit cell and significant modifications to the magnetic states-a crossover from ferromagnetism at room temperature for Ge-rich compounds to antiferromagnetism for Si-rich compounds. The compositional dependence of the room temperature lattice parameters exhibits non-linear behaviour around x = 1.2, reflecting the presence of magnetovolume effects. Re-entrant ferromagnetism has been observed in both PrMn2Ge1.0Si1.0 and PrMn2Ge0.8Si1.2 compounds with co-existence of canted ferromagnetism and canted antiferromagnetism detected, with both compounds exhibiting a larger unit cell volume in the canted Fmc state than in the canted AFmc.Combined with earlier studies of this system, the magnetic phase diagram has been constructed over the full range of PrMn2Ge2-xSix compositions (x = 0.0-2.0) and over the temperature range of interest (T = 3-480 K). In common with other systems in the RMn2X2 series, the overall magnetic behaviour of PrMn2Ge2-xSix compounds is governed by the strong dependence of the magnetic couplings on the Mn-Mn spacing within the ab-plane. Both total manganese moment [Formula: see text] and in-plane manganese moment [Formula: see text] at 5 K are found to decrease with increasing Si content, which can be ascribed to the reduction of Mn-Mn separation distance and stronger Si-Mn hybridization compared with Ge-Mn hybridization. Pr site ferromagnetic ordering occurs for x < 1.6 below Combined with earlier studies of this system, the magnetic phase diagram has been constructed over the full range of PrMn 2 Ge 2-x Si x compositions (x=0.0-2.0) and over the temperature range of interest (T=3-480 K). In common with other systems in the RMn 2 X 2 series, the overall magnetic behaviour of PrMn 2 Ge 2-x Si x compounds is governed by the strong dependence of the Confidential: not for distribution. Submitted to IOP Publishing for peer review 11 July 2013 2 magnetic couplings on the Mn-Mn spacing within the ab-plane. Both total manganese moment µ tot Mn and in-plane manganese moment µ ab Mn at 5 K are found to decrease with increasing Si content which can be ascribed to the reduction of Mn-Mn separation distance and stronger Si-Mn hybridization compared with Ge-Mn hybridization. Pr site ferromagnetic ordering occurs for x <1.6 below T C Pr .

Tuneable Magnetic Phase Transitions in Layered CeMn2Ge2-xSix Compounds

“…for CeMn 2 Ge 0.8 Si 1.2 at T = 200 K the unit cell volume V ~ 178.6 Å 3 for Fmc while V ~ 174.5 Å 3 for AFmc as listed in Table 2 ). This behaviour agrees well with the other re-entrant ferromagnetism systems 20 25 35 , with around 0.3% contraction of the unit cell observed when the magnetic state changes at T N inter from Fmc to AFmc in SmMn 2 Ge 2 35 .…”

“…At room temperature the x = 1.2 compound exhibits a mixture of ferromagnetic and antiferromagnetic states while compounds with x > 1.2 are purely antiferromagnetic. Similar tendencies in the composition dependence of the lattice constants have been detected in the related PrMn 2 Ge 2-x Si x system 25 26 . As is well known and as indicated above (see also Fig.…”

“…A set of neutron powder diffraction patterns was obtained for CeMn 2 Ge 2-x Si x compounds (x = 0.0–2.0) over the temperature range 4–450 K. Rietveld refinements were carried out on all patterns using the FULLPROF program package 24 which allows us to derive the structural and magnetic parameters. As explained fully in related articles 8 19 25 30 , the specific location of Mn atoms on the 4 d site in the ThCr 2 Si 2 structure (space group I4/mmm ) allows ready identification of various magnetic structures from key indicators in the neutron diffraction patterns as follows: Ferromagnetic ordering of the Mn atoms— hkl reflections with h + k = 2 n and l = 2 n (e.g. (112), (200) reflections).…”

Pressure induced magneto-structural phase transitions in layered RMn2X2 compounds (invited)

“…Indeed strain can be seen in the neutron diffraction from PrMn 2 Ge 2Àx Si x , even though instrumental factors dominate the measured peak widths. 2,5 Concentration dependent lattice and magneto-elastic strain components can be identified in the (110) and (002) reflections. The lattice component, which is largely independent of temperature, is seen in both (110) and (002) reflections while the magneto-elastic component is evident only in the (110) reflection at Ge/Si concentrations where Fmc and AFmc co-exist.…”

Phase gap in pseudoternaryR1−yRy′Mn2Wang1, Kennedy2, Campbell3 et al. 2013Phys. Rev. B

“…2,13,16 Magnetization and differential scanning calorimetry (DSC) were used to identify magnetic phase transitions 24 …”