Unusual properties of multilayer nanoisland magnetic systems: Supervortices, flat spin springs and optical nonreciprocity
3rd International Conference on Magnetism and Magnetic Materials
October 22-23, 2018 | Rome, Italy
Fedor Pudonin
P.N. Lebedev Physical Institute of RAS, Russia
Keynote: Res. Rev. J Mat. Sci
DOI: 10.4172/2321-6212-C6-028
Abstract
The paper presents the results of studies of original nanostructures - multilayer systems from magnetic nanoislands of the (FeNi/
Co)N type. Earlier in the metal nanoislands, we found photoconductivity in a wide spectral range (0.4-1.5 μm), anomalous
conductivity, etc. It was also found that those systems can detect at room temperature superweak magnetic fields H of less than
10-11T. The physical reasons for this high sensitivity are not fully understood, but it is clear that they are due to the unusual physical
properties of island systems. Metal nanoisland layers with a given effective thickness were grown by RF sputtering. For metal films,
a percolation threshold was found - d* (for FeNi and Co films d*~1.8 nm). Films for dd* - continuous.
Nanoisland were flat pancakes of rounded shape with lateral dimensions of 3-30 nm, and their effective thickness varied from 0.4
to 7.0 nm. Magnetization processes were investigated at room temperature by the magneto-optical Kerr effect (MOKE). In the
structures (FeNi/Co)N (N varied from 10 to 40), unidirectional magnetic anisotropy was observed, not associated with the wellknown
exchange anisotropy (the hysteresis loops did not have an exchange shift). It was suggested that the detected unidirectional
anisotropy is associated with the appearance in the structures of an unusual supervortical magnetization. In this case the vortex is not
concentrated in separate nanoislands, but is distributed over a certain set of them. Micromagnetic modeling confirmed the possibility
of the existence of a supervortical magnetization in the island structure. An indirect confirmation of the existence of such unusual
supervortical magnetization was the results of a study of the magnetization of the nanoislands layers on a SQUID magnetometer.
The presence of a supervortical magnetization leads the island structures to be chiral and leads to the appearance of an anomalous
optical nonreciprocity. In this report we discuss the possible causes of the appearance of optical nonreciprocity. However, the high
sensitivity of island structures to superweak magnetic fields, apparently, is not related to supervortex magnetization. For this reason
magnetization processes and magnetoresistance in special structures - bilayers [(FeNi/Co)-Al2O3]N were investigated. A region with
specific magnetization in FeNi nanoislands in a weak magnetic field is appeared. In those regions of FeNi islands the rotation of the
magnetization vector is occurred. Those regions we call a flat (two dimensions) spin springs. When the current flows through this
region, additional scattering of the electron spins takes place and an additional negative magnetoresistance occurs. We believe that
these spin springs can cause high sensitivity of island structures to weak magnetic fields.
Recent Publications
1. Boltaev A P, Pudonin F A, Sherstnev I A and Egorov D A (2017) Detection of the metal-insulator transition in disordered
systems of magnetic nanoislands. Journal of Experimental and Theoretical Physics 125(3):465-468.
2. Boltaev A P, N A Penin, A O Pogosov and Pudonin F A (2003) Detection of photoconductivity in hyperfine metal films in
the visible and infrared spectral regions. Journal of Experimental and Theoretical Physics 96(5):940-944.
3. Boltaev A P and Pudonin F A (2006) Effect of weak electric fields on the conduction in thin metal films. Journal of
Experimental and Theoretical Physics 103(3):436-440.
4. Boltaev A P, Pudonin F A, Sherstnev I A et al. (2017) Flat magnetic exchange springs as mechanism for additional
magnetoresistance in magnetic nanoisland arrays. Journal of Magnetism and Magnetic Materials 428:132-135.
5. Boltaev A P, Pudonin F A and Sherstnev I A (2011) Specific features of the magnetoresistance in multilayer systems of
magnetic nanoislands in weak magnetic fields. Physics of the Solid State 53(5):950.
Biography
Fedor Pudonin is the Head of Laboratory in P.N.Lebedev Physical Institute Russian Academy of Science, Russia. He is the chief researcher in the Laboratory of Heterogeneous Systems Physics.
E-mail: pudonin@sci.lebedev.ru
Menu