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I n t e r n a t i o n a l C o n f e r e n c e o n
Metal, Mining and
Magnetic Materials
Journal of Material Sciences
ISSN: 2321-6212
N o v e m b e r 0 1 - 0 2 , 2 0 1 8
P a r i s , F r a n c e
Metal and Magnetism 2018
Page 24
Israel Felner, J Mat. Sci. 2018, Volume:6
DOI: 10.4172/2321-6212-C7-032
F
ollowing the phase diagramof AFe2As2 (A=Ba, Sr) inwhich superconductivity
(SC) emerges from magnetic states and the similarity between AFe
2
As
2
and RFe
2
X
2
(R=La, Y and Lu, X=Si or Ge) systems, RFe
2
M
2
was proposed as
a potential candidate for a new high TC superconducting family containing
Fe-X (instead of Fe-As) layers as a structural unit. Dozens samples of RFe
2
-
xMxX
2
(M=Ni, Mn and Cu) materials were synthesized and measured for their
magnetic properties. None of these materials is SC down to 1.8 K. In all samples,
pronounced magnetic peaks appear at various temperatures up to 232 K for
YFe
2
Si
2
.
57
Fe Mössbauer studies confirm the absence of long range magnetic
ordering down to 5 K. On the other hand, traces for two SC phases (at T
C
=32
and 66 K) have been observed in inhomogeneous commercial and fabricated
amorphous carbon (a-C) doped with sulfur (a-CS). Non-SC a-CS samples, exhibit
pronounced peaks in their virgin zero-field-cooled (ZFC) curves at T
P
~50-80 K.
Around T
P
, the field-cooled (FC) curves cross the ZFC plots. Thus at a certain
temperature range ZFC>FC, this behaviour is irreproducible and disappears in
the second ZFC and/or the FC runs. The same peculiar observation (ZFC>FC)
was observed in two other unrelated systems: in chiral-based magnetic memory
devices where the components are: α-helix L-polyalanine, Au, Al
2
O
3
and Co or Ni
layers. The ZFC>FC phenomenon is observed only in the hard direction only. In a
pathological liver tissues, the unusual ZFC>FC phenomenon cannot be ascribed
to extra magnetic phases (oxygen), and are an intrinsic property of these three
unrelated systems. We assume that in the ground state of each system, the
intrinsic local magnetic moments are randomly distributed. In the first ZFC
runs, low dc magnetic fields, align these moments to flip along its direction in a
FMmanner up to the peak position. Above TP, an antiparallel exchange coupling
is more favoured and in the next ZFC and/or FC processes the net magnetic
moments are lower and cross the ZFC branches
Biography
Israel Felner has completed PhD in1973 from the Hebrew
University (HU) of Jerusalem, Israel and Postdoctoral studies
at UCSD, San-Diego, USA. Since 1973 to till date, he works at
the Racah Institute of Physics at the HU. He became a Full
Professor in 1995. He served as the Chairman of the Physics
Studies (2003-2006). His main interest topics are: Structural,
Magnetism and Mossbauer studies of Rare-earth inter-metallic,
High Tc superconductivity and Magneto-Superconducting
Materials and search for new High Tc Superconductors. He
published more than 510 papers in reputed journals. He serves
as a Chief-Editor of
Journal of Superconductivity and Novel
Magnetism and as an
Editorial Board Member
of Materials
Research Express journal
.
Israel.felner@mail.huji.ac.ilSearch for new high Tc superconductors and unusual
irreversible magnetic behaviour in three unrelated materials
Israel Felner
Racah Institute of Physics-The Hebrew University of Jerusalem, Israel