Site disorder and spin-glass ordering in PrAu2Si2

Ryan, D. H.; Voyer, C. J.; Swainson, I. P.; Krimmel, A.; Loidl, A.

doi:10.1063/1.1850271

Cited by 6 publications

(11 citation statements)

References 14 publications

(12 reference statements)

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“…The recent observation of spin-glass (SG) behaviour in the stoichiometric well-ordered intermetallic compound PrAu 2 Si 2 with tetragonal crystal structure is quite surprising, because presumably frustration and disorder are essential to induce a spin-glass state [1]. The structural disorder due to Au and Si site mixing in this compound is found to be less than 1% [2] and hence is excluded as the origin of SG behaviour in PrAu 2 Si 2 . URh 2 Ge 2 is another stoichiometric compound in which spin-glass behaviour is observed due to the site disorder on the rhodium and germanium sites [3].…”

Section: Introductionmentioning

confidence: 97%

Signatures of spin-glass behaviour in PrIr₂B₂and heavy fermion behaviour in PrIr₂B₂C

Anupam¹,

Anand²,

Hossain³

et al. 2011

J. Phys.: Condens. Matter

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The magnetic and transport properties of PrIr(2)B(2) and PrIr(2)B(2)C have been investigated by dc and ac magnetic susceptibility, specific heat, electrical resistivity and magnetoresistance measurements. PrIr(2)B(2) forms in CaRh(2)B(2)-type orthorhombic crystal structure (space group Fddd). At low fields the dc magnetic susceptibility of PrIr(2)B(2) exhibits a sharp anomaly near 46 K which is followed by an abrupt increase below 10 K with a peak at 6 K, and split-up in ZFC and FC data below 46 K. In contrast, the specific heat exhibits only a broad Schottky type hump near 9 K which indicates that there is no long range magnetic order in this compound. The thermo-remanent magnetization is found to decay very slowly with a mean relaxation time τ = 3917 s. An ac magnetic susceptibility measurement also observes two sharp anomalies; the peak positions strongly depend on the frequency and shift towards high temperature with an increase in frequency, obeying the Vogel-Fulcher law as expected for a canonical spin-glass system. The two spin-glass transitions occur at freezing temperatures T(f1) = 36 K and T(f2) = 3.5 K with shifts in the freezing temperatures per decade of frequency δT(f1) = 0.044 and δT(f2) = 0.09. An analysis of the frequency dependence of the transition temperature with critical slowing down, τ(max)/τ(0) = [(T(f)-T(SG))/T(SG)](-zν), gives τ(0) = 10(-7) s and exponent zν = 8, and the Vogel-Fulcher law gives an activation energy of 84 K for T(f1) and 27.5 K for T(f2). While zν = 8 is typical for spin-glass system, the characteristic relaxation time τ(0) = 10(-7) s is very large and comparable to that of superspin-glass systems. An addition of C in PrIr(2)B(2) leads to PrIr(2)B(2)C which forms in LuNi(2)B(2)C-type tetragonal structure (space group I4/mmm) and remains paramagnetic down to 2 K. The specific heat data show a broad Schottky type anomaly, which could be fairly reproduced with CEF analysis which suggests that the ground state is a CEF-split singlet and the first excited state singlet is situated 15 K above the ground state. The Sommerfeld coefficient γ∼300 mJ mol(-1) K(-2) of PrIr(2)B(2)C is very high and reflects a heavy fermion behaviour in this compound. We believe that the heavy fermion state in PrIr(2)B(2)C has its origin in low lying crystal field excitations as has been observed in PrRh(2)B(2)C.

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Section: Introductionmentioning

confidence: 97%

Signatures of spin-glass behaviour in PrIr₂B₂and heavy fermion behaviour in PrIr₂B₂C

Anupam¹,

Anand²,

Hossain³

et al. 2011

J. Phys.: Condens. Matter

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“…After extended annealing, single crystalline URh 2 Ge 2 transforms from a heavy fermion SG into a long-range antiferromagnetically ordered heavy fermion compound [10]. The SG behavior of PrAu 2 Si 2 , however, appears even in the best quality samples after extensive annealing [11]. On the other hand, it is well know that novel anisotropy in magnetic and transport behavior is usually observed in rare earth or uranium compounds with hexagonal structure.…”

Section: Introductionmentioning

confidence: 99%

Magnetic anisotropy and spin-glass behavior in single crystalline U₂PdSi₃

Kimura

Haga

et al. 2011

J. Phys.: Condens. Matter

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We present the magnetic and transport properties of single crystalline U(2)PdSi(3) measured with the magnetic field (H) (or measuring current, I) applied along two typical crystallographic directions, i.e. H ⊥ c-axis and H c-axis (or I ⊥ c-axis and I c-axis). For both directions, a spin-glass state is confirmed to form at low temperature with the same spin freezing temperature T(f) (=11.5 K), initial frequency shift δT(f) (=0.023) and activation energy E(a)/k(B) (=90.15 K) in zero dc field. Strong anisotropy in magnetic and transport behavior is found to be a significant feature of U(2)PdSi(3). The unusual ferromagnetic-like anomaly in ac susceptibility and dc magnetization curves around T(m)=71 K is observed in the case of H c-axis but not in the cases of H ⊥ c-axis. The characteristic temperature T(ir), below which evident irreversible magnetism originated from random spin freezing can be observed, shows much stronger field dependence for H ⊥ c-axis than for H c-axis. Moreover, an unusual finding is that the electrical resistivity measurements indicate the formation of magnetic Brillouin-zone boundary gaps and much larger magnetic scattering for I ⊥ c-axis, while the coherent-Kondo-effect-like behavior is obvious for I c-axis. We also emphasize that no resistivity minimum can be detected down to 2.5 K for either direction. The observed magnetic and transport behaviors are compared with those in polycrystalline U(2)PdSi(3) and other 2:1:3 intermetallic compounds.

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“…On the other hand, the spin glass behaviour of PrAu 2 Si 2 is very robust, and appears in the best quality samples after extensive annealing. A recent Mössbauer study, combined with neutron and x-ray diffraction, concluded that interchange of gold and silicon atoms was less than 1% [6]. Furthermore, the intentional introduction of disorder through the substitution of germanium for silicon stabilizes long-range antiferromagnetic order at concentrations greater than 12% [7].…”

mentioning

confidence: 99%

“…A recent Mössbauer study, combined with neutron and X-ray diffraction, concluded that interchange of gold and silicon atoms was less than 1% (ref. 6). Furthermore, the intentional introduction of disorder through the substitution of germanium for silicon stabilizes long-range antiferromagnetic order at concentrations greater than 12% (ref.…”

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confidence: 99%

Spin-glass order induced by dynamic frustration

et al. 2008

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Spin glasses are systems whose magnetic moments freeze at low temperature into random orientations without long-range order 1 . It is generally accepted that both frustration and disorder are essential ingredients in all spin glasses, so it was surprising that PrAu 2 Si 2 , a stoichiometric compound with a well-ordered crystal structure, was reported 2 to show spin-glass freezing. Here, we report on inelastic neutron scattering measurements of crystal-field excitations, which show that PrAu 2 Si 2 has a singlet ground state and that the exchange coupling is very close to the critical value to induce magnetic order. 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. This novel mechanism for producing a frustrated ground state could provide a method of testing the concept of 'avoided criticality' in glassy systems.Frustration arises from competing interactions that favour incompatible ground states 1,3 . For example, in rare-earth intermetallic compounds, the magnetic moments of the f electrons on each rare-earth site interact with neighbouring moments through Ruderman-Kittel-Kasuya-Yosida exchange interactions that oscillate in sign with increasing separation. 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. However, when there is disorder, in either the site occupations or the exchange interactions, the additional randomness can prevent a unique ordered ground state. Instead, these systems may form spin glasses, which possess a multitude of possible disordered ground states, into one of which the system freezes below the glass transition temperature, T g (ref. 1). In the thermodynamic limit, spin glasses show broken ergodicity, preventing significant fluctuations to any of the other degenerate spin configurations.In recent years, two stoichiometric intermetallic compounds have shown evidence of spin-glass order, URh 2 Ge 2 (ref. 4) and PrAu 2 Si 2 (ref. 2), both nominally with the same tetragonal (ThCr 2 Si 2 -type) crystal structure. In both samples, classic spin-glass behaviour was observed (T g = 11 K and 3 K, respectively), with a frequency-dependent peak in the Figure 1 Crystal-field transition in PrAu 2 Si 2 . Inelastic neutron scattering from PrAu 2 Si 2 measured at 1.5 K (red symbols) with error bars derived from the square root of the raw data counts. The solid line is a fit to the singlet-doublet crystal-field transition at ∆ = 0.7 meV (dashed line) and an elastic peak from nuclear incoherent scattering (dotted line). The shaded area represents double scattering from the transition at 2∆. The inset illustrates the mechanism for induced-moment formation, in which interionic exchange coupling, J ex , admixes the excited magnetic doublet into the singlet grou...

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Site disorder and spin-glass ordering in PrAu2Si2

Cited by 6 publications

References 14 publications

Signatures of spin-glass behaviour in PrIr₂B₂and heavy fermion behaviour in PrIr₂B₂C

Signatures of spin-glass behaviour in PrIr₂B₂and heavy fermion behaviour in PrIr₂B₂C

Magnetic anisotropy and spin-glass behavior in single crystalline U₂PdSi₃

Spin-glass order induced by dynamic frustration

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Site disorder and spin-glass ordering in PrAu2Si2

Cited by 6 publications

References 14 publications

Signatures of spin-glass behaviour in PrIr2B2and heavy fermion behaviour in PrIr2B2C

Signatures of spin-glass behaviour in PrIr2B2and heavy fermion behaviour in PrIr2B2C

Magnetic anisotropy and spin-glass behavior in single crystalline U2PdSi3

Spin-glass order induced by dynamic frustration

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Signatures of spin-glass behaviour in PrIr₂B₂and heavy fermion behaviour in PrIr₂B₂C

Signatures of spin-glass behaviour in PrIr₂B₂and heavy fermion behaviour in PrIr₂B₂C

Magnetic anisotropy and spin-glass behavior in single crystalline U₂PdSi₃