Magnetic structure in the zero-applied-field reentrant superconductor ErNi1.96Fe0.04B2C0.99

Abstract

ErNi1.96Fe0.04B2C0.99 is superconducting at Tc=7.3K and is shown to partially reenter the normal state between 5.5 and 5.7 K in zero applied field by means of ac-susceptibility (χac′) and resistivity measurements. Specific heat (Cp) measurements give a magnetic ordering temperature TN=5.7±0.2K. Powder neutron diffraction measurements showed that the Er3+ magnetic moments adopt below TN=5.9±0.2K a transverse modulated structure along the a axis (q=0.559a*). Observation of third-order and fifth-order harmonics indicates a squaring of the structure at lower temperature (8.2μB at 1.4 K). Although even-order peaks could not be detected in the neutron data, a weak ferromagnetic transition at TWFM=2.2K could be directly evidenced by magnetic susceptibility measurements and Cp measurements and indirectly evidenced in the thermal variations of the intensity of the first-order magnetic peaks (Iq), the magnetic coherence length (ξm), and the magnetic wave vector (q). The magnetic structure of ErNi1.96Fe0.04B2C0.99 is nearly identical to that of the parent compound ErNi2B2C. Precise comparison between the temperature variations of Iq, ξm, and χac′ shows that the transverse a*-modulated magnetic structure is responsible for the reentrant behavior between 5.5 and 5.7 K. Although it is still pair breaking below 5.5 K, it coexists with superconductivity. 57Fe Mössbauer spectra display no broadening in the temperature range where the reentrant behavior is observed, showing that the transferred hyperfine field at the Fe site, if any, is smaller than 2 kOe.

Source-reported materials — not catalogue approval

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