Crystal growth and ambient and high pressure study of the re-entrant superconductor Tm<SUB>2</SUB>Fe<SUB>3</SUB>Si<SUB>5</SUB>

Tm<SUB>2</SUB>Fe<SUB>3</SUB>Si<SUB>5</SUB> is known to undergo a transition to the superconducting state (at ambient or applied pressure depending on the sample) at a temperature T<SUB>c1</SUB>(~1.8 K), and at a lower temperature T<SUB>N</SUB>(&#8776;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<SUB>c2</SUB> = T<SUB>N</SUB>. The conditions reported in the literature for the observation of superconductivity in Tm<SUB>2</SUB>Fe<SUB>3</SUB>Si<SUB>5</SUB> are sample dependent, but it is now accepted that stoichiometric Tm<SUB>2</SUB>Fe<SUB>3</SUB>Si<SUB>5</SUB> superconducts only under pressure. Here we report single-crystal growth of stoichiometric Tm<SUB>2</SUB>Fe<SUB>3</SUB>Si<SUB>5</SUB> which does not superconduct at ambient pressure down to 100 mK. Measurements of the anisotropic static magnetic susceptibility &#967;(T) and isothermal magnetization M(H), ac susceptibility &#967;<SUB>ac</SUB>(T), electrical resistivity &#961;(T) and heat capacity C(T) at ambient pressure and &#967;<SUB>ac</SUB>(T) at high pressure are reported. The magnetic susceptibility along the c axis, &#967;<SUB>c</SUB>(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, &#967;<SUB>a</SUB>(T), follows a Curie-Weiss behavior between 130 and 300 K with a Weiss temperature &#952; and an effective magnetic moment &#956;<SUB>eff</SUB> which depend on the temperature range of the fit. The easy axis of magnetization is perpendicular to the c axis and &#967;<SUB>a</SUB>/&#967;<SUB>c</SUB> = 3.2 at 1.8 K. The ambient pressure &#967;<SUB>ac</SUB>(T) and C(T) measurements confirm bulk antiferromagnetic ordering at T<SUB>N</SUB> = 1.1 K. The sharp drop in &#967;<SUB>ac</SUB>(T) below the antiferromagnetic transition is suggestive of the existence of a spin gap. We observe superconductivity only under applied pressures P&#8805;2 kbar. The temperature-pressure phase diagram showing the non-monotonic dependence of the superconducting transition temperature T<SUB>c</SUB> on pressure P is presented