Crystal growth and ambient and high pressure study of the re-entrant superconductor Tm₂Fe₃Si₅

Abstract

Tm₂Fe₃Si₅ is known to undergo a transition to the superconducting state (at ambient or applied pressure depending on the sample) at a temperature T_c1(~1.8 K), and at a lower temperature T_N(≈1 K) it undergoes a transition into a long range antiferromagnetically ordered state. Superconductivity is simultaneously destroyed and the sample re-enters the normal state at T_c2 = T_N. The conditions reported in the literature for the observation of superconductivity in Tm₂Fe₃Si₅ are sample dependent, but it is now accepted that stoichiometric Tm₂Fe₃Si₅ superconducts only under pressure. Here we report single-crystal growth of stoichiometric Tm₂Fe₃Si₅ which does not superconduct at ambient pressure down to 100 mK. Measurements of the anisotropic static magnetic susceptibility χ(T) and isothermal magnetization M(H), ac susceptibility χ_ac(T), electrical resistivity ρ(T) and heat capacity C(T) at ambient pressure and χ_ac(T) at high pressure are reported. The magnetic susceptibility along the c axis, χ_c(T), shows a curvature over the whole temperature range and does not follow the Curie-Weiss behavior, while the magnetic susceptibility along the a axis, χ_a(T), follows a Curie-Weiss behavior between 130 and 300 K with a Weiss temperature θ and an effective magnetic moment μ_eff which depend on the temperature range of the fit. The easy axis of magnetization is perpendicular to the c axis and χ_a/χ_c = 3.2 at 1.8 K. The ambient pressure χ_ac(T) and C(T) measurements confirm bulk antiferromagnetic ordering at T_N = 1.1 K. The sharp drop in χ_ac(T) below the antiferromagnetic transition is suggestive of the existence of a spin gap. We observe superconductivity only under applied pressures P≥2 kbar. The temperature-pressure phase diagram showing the non-monotonic dependence of the superconducting transition temperature T_c on pressure P is presented.