Quantum phase transition in a partially frustrated heavy-fermion system: CePdAl

Hilbert von Löhneysen

Karlsruher Institut für Technologie

Physikalisches Institut and Institut für Festkörperphysik

76131 Karlsruhe, Germany


    The heavy-fermion compound CePdAl orders antiferromagnetically below the Néel temperature TN = 2.7 K [1]. In the hexagonal ZrNiAl-type crystal structure adopted by CePdAl, the triangular site symmetry of the magnetic Ce ions gives rise to geometrical frustration. Indeed, neutron scattering experiments [2] indicate partial frustration of the Ce moments in CePdAl, i.e., only two thirds of the Ce ions participate in the long-range magnetic order, rendering this system a promising candidate for the investigation of the effect of frustration on quantum critical behavior. Frustration offers a different route from a magnetic to a nonmagnetic ground state besides that adopted by heavy-fermion systems where usually the competition between RKKY interaction and Kondo effect governs quantum criticality. In CePdAl, TN can be suppressed by either hydrostatic pressure [3] or partial substitution of Pd by Ni [4]. However, a detailed analysis of a possible antiferromagnetic quantum critical point has not been made. We have investigated the low-temperature specific heat C(T) and magnetization of CePd1-xNixAl polycrystals. C(T) measured at p = 0 evolves toward C/T ~ ln (TO/T) at the critical concentration x ≈ 0.144.

    In order to study this system in more detail, we have grown large single crystals of CePd1-xNixAl by the Czochralski method. The magnetization displays a strong magnetic anisotropy, which is preserved in the Ni-doped compounds. Neutron diffraction experiments confirm the partial frustration and indicate that short-range correlations persist to temperatures well above TN. The thermal expansion and magnetostriction of CePdAl measured in magnetic fields up to B = 14 T parallel to the c axis are used to clarify whether an anisotropic distortion of the unit cell can lift the frustration of the remaining Ce moments and to establish the magnetic phase diagram.

  


[1] C. Schank et al., J. Alloys Comp. 207/208, 329 (1994)

[2] A. Dönni et al., J. Phys.: Condens. Matter 8, 11213 (1996)

[3] T. Goto et al., J. Phys. Chem. Solids 63, 1159 (2002)

[4] Y. Isikawa et al., J. Phys. Soc. Jpn. 65, 117 (1996)


*Work done in collaboration with N. Bagrets, V. Fritsch, K. Grube, O.   Stockert, S. Woitschach and S. Zaum

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