The effect of pressure on the low energy spin fluctuations inCeAl2 investigatedthrough 27Al nuclear quadrupole resonance and nuclear magnetic resonance measurements

Abstract

To microscopically elucidate the initial evolution of the electronic and magnetic states of a Kondo compoundCeAl2 (Néeltemperature TN∼3.8 K) from the antiferromagnetically ordered state with a spin density waveto a magnetic quantum critical point with the application of pressureP, we havecarried out 27Al nuclear quadrupole resonance and magnetic resonance measurements forP = 0 and 2.5 GPa. The Knight shift, which is proportional to the uniform susceptibility , exhibits a rapid increase below∼50 K downto TN for each pressure, indicating that the sufficiently localized f electron doesnot directly participate in the formation of the Fermi surface even atP = 2.5 GPa. The nuclear spin–lattice relaxation measurements and the analysis leadto the conclusion that the cf hybridized band with a rather large densityof states at the Fermi level is formed below an onset temperature aboveTN, the value of which increases with the application of pressure. The relaxation rate in theparamagnetic state is dominated by the generalized susceptibility that has peaks near the antiferromagnetic wavevector associated with the nesting properties of the Fermi surface of the underlyingcf hybridized band. With decreasing temperature, also exhibits a significant increase larger than that ofχ(0). The finite pressure of 2.5 GPa has the effect of reducing bothχ(0) and χ(QAF) by about 20% in their magnitudes. Then, changes in the nesting conditionwith pressure are conjectured to play an important role in depressing themagnetic ordering, in addition to the increase in the extent of mixingJcf between the localized f electrons and conduction electrons.