Volume 73, Number 5, March 2006
|Page(s)||772 - 778|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||27 January 2006|
Observation of the spontaneous vortex phase in the weakly ferromagnetic superconductor : A penetration depth study
Department of Physics, University of Illinois at Urbana-Champaign 1110 W. Green Street, Urbana IL 61801, USA
2 Los Alamos National Laboratory, MST-10 - Los Alamos, NM 87545, USA
3 National Creative Research Initiative Center for Superconductivity and Department of Physics, Pohang University of Science and Technology Pohang 790-784, Republic of Korea
4 National Institute for Materials Science - 1-2-1 Sengen Tsukuba, Ibaraki 305-0047, Japan
Accepted: 13 January 2006
The coexistence of weak ferromagnetism and superconductivity in suggests the possibility of a spontaneous vortex phase (SVP) in which vortices appear in the absence of an external field. We report evidence for the long-sought SVP from the in-plane magnetic penetration depth of high-quality single crystals of . In addition to expected features at the Néel temperature and weak ferromagnetic onset at , rises to a maximum at before dropping sharply down to . We assign the maximum to the proliferation and freezing of spontaneous vortices. A model proposed by Koshelev and Vinokur explains the increasing as a consequence of increasing vortex density, and its subsequent decrease below Tm as defect pinning suppresses vortex hopping.
PACS: 74.25.Nf – Response to electromagnetic fields (nuclear magnetic resonance, surface impedance, etc.) / 74.25.Ha – Magnetic properties / 74.70.Dd – Ternary, quaternary and multinary compounds (including Chevrel phases, borocarbides, etc.)
© EDP Sciences, 2006
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