Matter. and B.D.R. Nature Phys 4, 766–770 (2008). Blanco, J. Phys. 12), Pr3Tl (ref. Rev. Tarjus, G., Kivelson, S. A., Nussinov, Z. A self-consistent mean-field calculation of the phase diagram of PrAu2(Si1−xGex)2 as a function of the interionic exchange energy, Jex, for a singlet–doublet transition energy, Δ=0.7 meV. 1, 17–23 (1976). Google Scholar. and M.K., with samples produced by R.T.M. 15 in a mean-field model developed to explain scandium–terbium alloys16 and PrP0.9 (ref. The peak widths are inversely proportional to the lifetimes of the excited states, which, in metals, are limited by conduction-electron scattering. 4a). Sherrington calculated that a sufficiently large distribution of exchange interactions, δJ Rev. J. Appl. It was quickly established that spin-glass freezing in the uranium compound resulted from site disorder on the rhodium and germanium sublattices. Spin-glass order induced by dynamic frustration. However, in the presence of static disorder, the low-temperature phase could also be a spin glass, as shown in ref. It is generally accepted that both frustration and disorder are essential ingredients in all spin glasses, so it was surprising that PrAu2Si2, a stoichiometric compound with a well-ordered crystal structure, was reported to exhibit spin glass freezing. Nature 421, 483 (2003). Abstract. Observation of a central mode in an exchange-coupled singlet-groundstate system. The concept of frustration in spin glasses. So how can spin-glass behaviour emerge in … Phys. Phys. 7). Except for specific classes of geometrically frustrated lattices, well-ordered crystal structures produce either ferromagnetic or antiferromagnetic order, depending on the energy minimization of the interactions between all the neighbouring moments. We thank A. Murani and R. Stewart for scientific discussions and assistance with the ILL experiments. It was therefore surprising that PrAu 2 Si 2 was reported to show all the characteristics of a spin glass, even though it is a stoichiometric compound with a well-ordered crystal structure. 6). Which is just as well, as I’m effing and blinding to her about that small propco we’d pitched to picking a rival PR company instead. Internet Explorer). In a two-level system, this temperature is given in a mean-field model by. Jensen, J., McEwen, K. A. The shaded area represents double scattering from the transition at 2Δ. This shows that there is no correlation between the measured inhomogeneous broadening and the transition to long-range antiferromagnetic order and confirms that static disorder is not the critical factor determining the occurrence of spin-glass freezing. Get the most important science stories of the day, free in your inbox. Phys. This scenario is similar to the ‘avoided criticality’ discussed in the theory of structural glass transitions by Tarjus et al. 3). R.T.M. The evolution from long-range magnetic order to spin-glass behaviour in PrAu2(Si1−xGex)2 . Chem. The light areas represent regions of induced-moment stability. 50, 690–693 (1983). & Coles, B. R. Spin-glass to Overhauser-alloy transitions in Yt–rare-earth and Sc–rare-earth alloys. (2020), Scientific Reports wrote the paper after extensive discussions with the other coauthors. & Stirling, W. G. Magnetic excitations in the longitudinally polarized antiferromagnetic phase of praseodymium. Lindgård, P.-A. ADS  The red (blue) symbols are the antiferromagnetic transition (spin-glass freezing) temperatures as a function of x. This article seeks to explain the origin of magnetic frustration in PrAu2Si2, given that conventional models involving static disorder or lattice topology do not seem to apply. Mater. J. Magn. 1). 17). Phys. B 56, 11666–11672 (1997). Spin glasses are considered here as representative of a new vast class of condensed matter phases … Figures The peak lineshape is modelled by the convolution of a Lorentzian and a Gaussian function. Before discussing the origin of spin-glass behaviour, we review what is known about magnetic order in singlet ground-state systems. The estimated range of Jex with spin-glass order is represented by the blue line. Krimmel, A. et al. B 27, 448–455 (1983). A calculation of Tc as a function of Jex for Δ=0.7 meV and n=2 is shown in Fig. By continuing you agree to the use of cookies. and JavaScript. B 35, 3327–3340 (1987). J. Phys. Phys. To obtain At larger values of δ Jex, spin-glass order would supersede long-range order. Grover, B. Dynamical properties of induced-moment systems. We propose that spin-glass freezing results from dynamic fluctuations of the crystal-field levels that destabilize the induced moments and frustrate the development of long-range magnetic correlations. 22. Historically, this subject was stimulated by the observation of spin-glass freezing in disordered alloys and compounds, and has more recently focused on systems where the lattice geometry produces a macroscopic degeneracy of possible spin configurations. The spin glass transition is from the paramagnetic state with q=0 to a spin glass state with nonzero q as the temperature is decreased. Houmann, J. G. et al. In induced-moment systems, a precursor of long-range order is the appearance in neutron scattering of a quasielastic ‘central’ peak close to the wavevector of the ordered phase, which is caused by fluctuating regions of short-range magnetic order20. The important result is that the width remains substantial down to the lowest temperature, with the full-width at half-maximum only falling to a value of 43% of the transition energy at the glass transition. We propose that relaxational broadening of the singlet–doublet transition provides the key. & Bucher, E. Magnetic excitons in singlet-ground-state ferromagnets. Germanium doping should therefore be an ideal way of enhancing the exchange disorder that is central to the Sherrington model. This shows that Jex increases by a factor of four from x=0 to 1., Physica B: Condensed Matter Krimmel, A. et al. Phys. The remaining levels are all above 7 meV, so this is effectively a two-level system at temperatures close to the glass transition. B 6, 2730–2743 (1972). Spin glasses are systems whose magnetic moments freeze at low temperature into random orientations without long-range order. We have used neutron scattering to study samples of PrAu2(Si1−xGex)2, with x=0, 0.05, 0.10, 0.15, 0.20, 0.80 and 1, which were synthesized by arc melting followed by annealing in vacuum for four weeks at 850 ∘C. 1). It had already been found that long-range antiferromagnetism in PrAu2(Si1−xGex)2 is stabilized at concentrations x>0.12 (ref. It was therefore surprising that PrAu 2 Si 2 was reported to show all the characteristics of a SG, even though it is a stoichiometric compound with … The presence of frustration and disorder are necessary ingredients for an SG transition. Fischer, K. H. & Hertz, J. 97, 10A908 (2005). If we convolve the peak lineshape with the instrumental resolution to produce the fits in Fig. Transitions between the crystal-field levels can be observed directly by neutron scattering as inelastic peaks, whose energies and intensities can be used to refine the parameters of the crystal-field potential. The error bars come from the numerical fits to the peak lineshape described in the legend of Fig. Matter 17, R1143–R1182 (2005). Thank you for visiting 27, 1530–1533 (1971). Goremychkin, E. A., Osborn, R., Rainford, B. D., Adroja, D. T. & Koza, M. Magnetic dynamics of the spin-glass system PrAu2Si2: An inelastic neutron scattering study. Rev. Sci. Site disorder and spin-glass ordering in PrAu2Si2 . J. Phys. C 12, L929–L933 (1979). The doublet states have finite magnetic moments, but the singlet states are non-magnetic, except in the presence of exchange interactions with neighbouring sites as discussed below. In Fig. Ryan, D. H. et al. Magn. Article  The mean-field calculation of the phase diagram of PrAu2Si2 and PrAu2Ge2 as a function of crystal-field energy Δ for the respective values of Jex (Fig. Rev. Dedicated to Professor B. T. Matthias in celebration of his 60th birthday. Rev. As the ground state of the isolated ion is non-magnetic, a magnetic moment can result only from an admixture of excited crystal-field states produced by exchange interactions with neighbouring praseodymium ions.


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