Abstract
We report a study on tuning the charge density wave (CDW) ferromagnet SmNiC2 to a weakly coupled superconductor by substituting La for Sm. X-ray diffraction measurements show that the doped compounds obey Vegard’s law, where La (Lu) alloying expands (shrinks) the lattice due to its larger (smaller) atomic size than Sm. In the series Sm1−xLaxNiC2, CDW transition (TCDW = 148 K) for SmNiC2 is gradually suppressed, while the ferromagnetic (FM) ordering temperature (TC) at 17 K slightly increases up to x = 0.3. For x > 0.3, TC starts to decrease and there is no signature that could be related with the CDW phase. Electrical resistivity, magnetic susceptibility and specific heat measurements point toward the possible presence of a FM quantum critical point (QCP) near x = 0.92, where the TC is extrapolated to zero temperature. Superconductivity in LaNiC2 (Tsc = 2.9 K) is completely suppressed with small amount of Sm inclusion near the proposed FM critical point, indicating a competition between the two ordered phases. The tunable lattice parameters via chemical substitution (La,Lu) and the ensuing change among the ordered phases of ferromagnetism, CDW and superconductivity underscores that SmNiC2 provides a rich avenue to study the rare example of a FM QCP, where the broken symmetries are intricately correlated.
Highlights
In SmNiC2, the low-temperature synchrotron x-ray diffraction reveals that a charge density wave (CDW) state with the wave vector q =(0.5, 0.52, 0) forms below 148 K and disappears below the Curie temperature 17.7 K, indicating destruction of the CDW due to appearance of the ferromagnetic ordering[12]
Electrical resistivity and heat capacity data point toward the possible presence of a FM quantum critical point near x = 0.92, where the Curie temperature TC is extrapolated to zero temperature and the specific heat divided by temperature is strongly enhanced with decreasing temperature down to the lowest measuring temperature
La alloying in SmNiC2 expands the lattice parameters, while Lu alloying shrinks the lattice parameters
Summary
In SmNiC2, the low-temperature synchrotron x-ray diffraction reveals that a CDW state with the wave vector q =(0.5, 0.52, 0) forms below 148 K and disappears below the Curie temperature 17.7 K, indicating destruction of the CDW due to appearance of the ferromagnetic ordering[12]. This is different from NdNiC2 where a CDW is still observed below the Nèel temperature (in the AFM state)[13]. Superconductivity in the first member of RNiC2 family, LaNiC2 with Tsc = 2.9 K, was first reported by W. Comprehensive magnetic and superconducting phase diagram for both Sm1−xLayNiC2 and Sm1−yLuyNiC2 is constructed for the first time
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