Search for Superconductivity of Magnetic Metals under Pressure

1.实现了低至30 mK的低温和高达200 GPa的高压的复杂条件。开发了极端条件下的电、磁、光测量实验技术.研究铁在压力下的非磁性状态下的超导性是通过以下过程进行的; a.铁的提纯在超高真空中进行。B.纯化后的样品在NaCl压力介质中用金刚石压砧（DAC）加压。C.电阻和磁化强度的测量是在压力的增加和减少过程中进行的.结果通过电阻的下降发现了超导电性的开始，通过迈斯纳效应的检测也证实了这一点。得到了温度-压力相图。Tc在15 GPa时出现在bcc相转变为hep相之后，在30 GPa时消失。Tc和Hc的最大值分别为2K和2000 Oe.（1）低温强磁场下的穆斯堡尔谱实验证实了铁在hep相中的磁性是由传导电子引起的（泡利帕拉磁性）。(2)进行了第一原理能带计算，给出了Tc的估计。(3)我们还研究了反铁磁Mn的情况。我们发现，在9 GPa附近，Neel温度Tn消失，但即使对于纯化的样品，也没有发现超导性的迹象。(4)本文用电阻法和热容法详细研究了铁磁体UGe_2的压致超导电性，并确定了Tc -压力相图。

1. Complex condition of low temperature down to 30mK and high pressure up to 200GPa is achieved. experimental techniques for electrical, magnetic and optical measurement under extreme conditions are developed.2. Search for superconductiyity of iron in its non - magnetic state under pressure are performed by the following procedure ; a. Purification of iron is performed in ultra high vacuum. b. Purified sample is pressed in NaCl pressure media by diamond anvil cell (DAC). c. Electrical resistance and magnetization measurement are performed in the course of both inereasing and decreasing process of pressure.3. ResultsOnset of superconductivity is found by the drop of electrical resistance and also confirmed by the detection of Meissner effect. Temperature vs pressure phase diagram is obtained. Tc appears at 15GPa just after the crystal phase transition from bcc to hep phase and disappears at 30GPa. The maximum of Tc and Hc is 2K and 2000Oe respectively.4. Other Results(1) Mossbauer experiment under low temperature and high magnetic field is performed and we confirmed the magnetism of iron at hep phase was due to conduction electron )pauli para magnetism).(2) The first principle band calculation is performed and estimation of Tc is given.(3) We have also studied the case of antiferromagnetic Mn. We found that the Neel temperature Tn disappears at around 9GPa but no sign of superconductivity is found yet even for purified sample.(4) Pressure induced superponductiyity of ferromagnet UGe_2 is studied in detail by electrical resistance and heat capacity measurement and determined the Tc - pressure phase diagram.