ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
The interplay between superconductivity (SC) and ferromagnetism (FM) in dilute magnetic alloys and intermetallic compounds attracted considerable attention during the last 30 years. Usually the ferromagnetic state is more stable and therefore tends to suppress SC. On the other hand, the magnetic state can be changed due to a modification of the RKKY interaction in the SC state. Mutual influence of SC and FM may acquire new peculiarities in such artificial systems as FM/SC multilayers. This work is focused on the study of Fe/Nb multilayered system, prepared on Al2O3(112¯0) substrates by rf-sputtering and by molecular beam epitaxy (MBE) techniques. The Nb thickness tNb was varied from 150 to 500 A(ring) and the Fe thickness tFe was changed from 5 to 100 A(ring). The sputtered samples were highly layered with sharp interfaces as revealed by x-ray reflectivity and were textured in the [110] direction. The epitaxial MBE samples showed (110) growth of Nb and Fe with a coherence lengths comprising the total film thickness. Surface and interface roughnesses were very small. The dependence of the ferromagnetic resonance (FMR) spectra parameters on the direction of the dc magnetic field rotating in the plane of the samples show sixfold anisotropic behavior indicating the well known three-domain in-plane structure of Fe layers on sapphire substrates.FMR and SQUID measurements showed that FM of Fe layers survived down to tFe=10 A(ring). The out-of-plane FMR measurements also showed that the easy axis of magnetization lies in the plane of the samples down to this thickness. The superconducting transition temperature Tc was determined by measurements of the electrical resistivity and by SQUID measurements. It was established that there is a critical thickness of the Fe layer tFecrit above which SC was not detected for temperatures down to 1.5 K. This value was dependent on tNb. Thus, for example, it was found that for tNb=300 A(ring) the value of tFecrit=30 A(ring) and for tNb=350 A(ring)—tFecrit=50 A(ring). For constant tFe with increasing tNb up to a certain thickness, SC was not detected; then Tc started to increase, and, finally, it approached the constant value of the order of 6 K above a certain tNb which depended on tFe. The critical magnetic field HC2 obtained from the resistivity measurements, strongly decreased with increasing tFe or decreasing tNb. The temperature dependences of HC2 were typical for two-dimensional superconductors. For the interpretation of the data obtained, various theories were employed. © 1996 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.362042
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