Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China.
J Phys Condens Matter. 2010 Jun 16;22(23):235701. doi: 10.1088/0953-8984/22/23/235701. Epub 2010 May 21.
In single crystals of Eu(1-x)Sr(x)Fe(2-y)Co(y)As(2), Co doping suppresses spin-density wave (SDW) ordering and induces a superconducting transition. A resistivity reentrance due to the antiferromagnetic ordering of Eu(2+) spins is observed, indicating the competition between antiferromagnetism (AFM) and superconductivity (SC). It is striking that the resistivity reentrance can be completely suppressed by a small magnetic field due to a field-induced metamagnetic transition from AFM to ferromagnetism (FM). The resistivity reentrance can also be suppressed by the substitution of Eu(2+) ions with nonmagnetic Ba(2+)/Sr(2+) to completely destroy the AFM ordering. These results indicate that the AFM order appears destructive to SC, while FM can coexist with the superconductivity. Further we find that magnon excitation exists in AFM ordering and can be suppressed by an applied field. Coexistence of SC from the FeAs layer and the inner field produced by the ferromagnetic Eu(2+) layer suggest a possible p-wave component in the superconducting order parameter.
在 Eu(1-x)Sr(x)Fe(2-y)Co(y)As(2) 的单晶中，Co 掺杂抑制了自旋密度波 (SDW) 有序，并诱导了超导转变。观察到由于 Eu(2+) 自旋的反铁磁有序引起的电阻率再进入现象，表明反铁磁 (AFM) 和超导 (SC) 之间存在竞争。引人注目的是，由于 AFM 到铁磁 (FM) 的磁场诱导变磁性转变，电阻率再进入可以被小磁场完全抑制。电阻率再进入也可以通过用非磁性 Ba(2+)/Sr(2+) 取代 Eu(2+) 离子来抑制，从而完全破坏 AFM 有序。这些结果表明，AFM 有序对 SC 具有破坏性，而 FM 可以与超导共存。进一步我们发现，在 AFM 有序中存在磁振子激发，并可以被外加磁场抑制。来自 FeAs 层的 SC 和由铁磁 Eu(2+) 层产生的内场共存表明超导序参量中可能存在 p 波分量。
