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Crossover from divalent to valence fluctuating state of Eu in EuCu2(Ge1−x Six)2 probed by 63,65Cu - NMR

“…This could be due to local disorder around Cu created by the substitution of larger Ge by smaller Si ions. In the Heavy Fermion metal CeCu 2 Si 2 , Ge-substitutions above 1% induces antiferromagnetic order, and no remarkable disorder effects are reported [3,6]. Furthermore a large Knight shift anisotropy (A hf ¼ À4:2 kOe/m B (||c) and +1.5 kOe/m B (?c)) was found [3,6].…”

Novel superconductivity at the magnetic critical point in heavy-fermion systems: a systematic study of NQR under pressure

“…It is, therefore, considered that the AFM in CeCu 2 (Si 0.98 Ge 0.02 ) 2 is not triggered by some disorder effect but by the intrinsic lattice expansion due to the Ge doping. In order to demonstrate a systematic evolution of lowenergy magnetic excitations at the paramagnetic state, the inset of figure 3 shows the T dependence of 1/T 1 T in CeCu 2 (Si 0.98 Ge 0.02 ) 2 at P = 0 GPa (closed circles) and 0.91 GPa (closed squares) along with the results in Ce 0.99 Cu 2.02 Si 2 at P = 0 GPa (open squares) and 0.85 GPa (open triangles) 14,24 . The result of 1/T 1 T in CeCu 2 (Si 0.98 Ge 0.02 ) 2 at P = 0 GPa is well explained by the spin-fluctuations theory for weakly itinerant AFM in T c < T < 1.5 K around T N ∼ 0.75 K 14,24,33 .…”

“…In order to demonstrate a systematic evolution of lowenergy magnetic excitations at the paramagnetic state, the inset of figure 3 shows the T dependence of 1/T 1 T in CeCu 2 (Si 0.98 Ge 0.02 ) 2 at P = 0 GPa (closed circles) and 0.91 GPa (closed squares) along with the results in Ce 0.99 Cu 2.02 Si 2 at P = 0 GPa (open squares) and 0.85 GPa (open triangles) 14,24 . The result of 1/T 1 T in CeCu 2 (Si 0.98 Ge 0.02 ) 2 at P = 0 GPa is well explained by the spin-fluctuations theory for weakly itinerant AFM in T c < T < 1.5 K around T N ∼ 0.75 K 14,24,33 . The good agreement between the experiment and the calculation indicates that a long-range nature of the AFM is in the itinerant regime.…”

“…Furthermore, the transport, thermodynamic and NQR measurements consistently indicated that nominally off-tuned Ce 0.99 Cu 2.02 Si 2 is located just at P c and crosses its QCP by applying a minute pressure of P = 0.2 GPa 14,23 . The magnetic and superconducting properties in CeCu 2 Si 2 were investigated around the QCP as the functions of P for Ce 0.99 Cu 2.02 Si 2 just at the border to AFM and of Ge content x for CeCu 2 (Si 1−x Ge x ) 2 by Cu-NQR measurements 14,24 . Figure 2 shows the phase diagram referred from the literature 24 .…”

“…The magnetic and superconducting properties in CeCu 2 Si 2 were investigated around the QCP as the functions of P for Ce 0.99 Cu 2.02 Si 2 just at the border to AFM and of Ge content x for CeCu 2 (Si 1−x Ge x ) 2 by Cu-NQR measurements 14,24 . Figure 2 shows the phase diagram referred from the literature 24 . Here, T * F is an effective Fermi temperature below which the nuclear-spinlattice-relaxation rate divided by temperature (1/T 1 T ) stays constant and T m is a temperature below which the slowly fluctuating antiferromagnetic waves start to develop.…”