The evolution from long-range magnetic order to spin-glass behaviour in PrAu₂(Si_1-xGe_x)₂

Abstract

We have studied the magnetic behaviour of PrAu2(Si1-xGex)2 by means of magnetic susceptibility, resistivity, and heat capacity measurements, and x-ray and neutron powder diffraction. All compounds are isostructural and crystallize in the well known ThCr2Si2-type structure. PrAu2Si2 shows the characteristic features of a canonical spin glass with a freezing temperature of TF = 3 K. Completely unexpectedly, on introducing/increasing the atomic disorder by alloying with Ge, the spin-glass transition is suppressed as is first evident from a slight decrease of the freezing temperature TF up to x = 0.10. Long-range magnetic order sets in for x0.12. Within the range 0.15 x1, all compounds show the same simple AF-I-type antiferromagnetic structure with a monotonic increase of both the Néel temperature and the ordered magnetic moment for increasing Ge concentration. The magnetic phase diagram of PrAu2(Si1-xGex)2 is explained by the presence of weak disorder at a constant level at the Au sites. Clear indications of crystal-field effects have been observed.

Magnetic, electronic and transport properties of RAg2Ge2 (R=Pr, Nd) compounds

“…Temperature variations of specific heat of PrFe 2 X 2 (XZSi, Ge) indicate a crystal field energy level scheme characterized as a ground state by two closely spaced singlets for both compounds. For the isostructural PrT 2 X 2 (TZCo, Cu, Ru; XZSi, Ge), PrNi 2 Si 2 and PrAu 2 Ge 2 [26] neutron diffraction data reveal antiferromagnetic order at low temperatures.…”

Magnetic ordering in PrT2Ge2 (T = Ni, Ru and Rh) compounds

“…These discrepancies are probably connected with the influence of the crystal electric field discussed in detail in Ref. [6]. For non-magnetic singlet ground CEF states, as expected in case of Pr ions, the magnetic ordering may appear due to admixing of the higher levels into the ground state due to magnetic exchange interactions.…”

“…6). Their positions can be indexed by assuming an incommensurate propagation vector k ¼ [0, 0, k z ] with k z ¼ 0.210 (6). Rietveld analysis of the neutron data yields an amplitude modulated magnetic structure with the magnetic moment amplitude of m 0 (k) ¼ 3.60(15) m B .…”

“…The hitherto investigations of the PrT 2 X 2 compounds revealed collinear antiferromagnetic orderings described by propagation vector k ¼ (0,0,1) (AFI-type [2]) in PrCu 2 X 2 (X ¼ Si, Ge) [3,4], PrRh 2 Si 2 [5], and PrAu 2 Ge 2 [6] or propagation vector k ¼ (0, 0, ½) in PrFe 2 X 2 [7,8]. In turn, sine-modulated magnetic structures with k ¼ (0, 0, k z ) were established for PrNi 2 Si 2 [9,10], PrCo 2 Ge 2 [11,12] and PrPd 2 Ge 2 [13].…”

“…In contrast, the compounds PrRu 2 X 2 (X ¼ Si, Ge) [15,16] and PrOs 2 Si 2 [17] order ferromagnetically. In turn, spin-glass behaviour was reported for PrAu 2 Si 2 [6] and PrAg 2 Ge 2 [14]. The data concerning the magnetic properties of the above mentioned compounds are summarized in Refs.…”