Search for Superconductivity of Magnetic Metals under Pressure

1.实现了低温至30mK、高压高达200 Gpa的复杂条件。发展了在极端条件下进行电、磁和光测量的实验技术。研究铁在压力下非磁性状态的超导性是通过下列步骤进行的：a.在超高真空中进行铁的提纯。B.提纯样品在氯化钠压力介质中用金刚石顶压室(DAC)压制。C.在升压和降压过程中都进行了电阻和磁化强度测量。结果通过电阻的下降和迈斯纳效应的检测证实了超导电性的存在。得到了温度-压力相图。Tc在15 GPa时刚从体心立方相转变为HEP相后出现，在30 GPa时消失。Tc和Hc的最大值分别为2K和2000Oe。其他结果(1)进行了低温强磁场下的穆斯堡尔实验，证实了HEP相铁的磁性是由于传导电子(泡利顺磁).(2)进行了第一主带计算，并给出了T_c的估算.(3)我们还研究了反铁磁性的情况.我们发现，在9 Gpa附近，Neel温度Tn消失了，但即使是提纯的样品也没有发现超导的迹象。(4)通过测量电阻和热容，详细研究了铁磁UGe_2的压致超导性，并测定了T_c-压强相图。

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.