J Supercond Nov Magn (2016) 29:41–46
DOI 10.1007/s10948-015-3238-8
ORIGINAL PAPER
Field-dependent Behavior of AC Susceptibility
in [Y
0.8
Ca
0.2
](Ba
0.5
Sr
0.5
)
2
Cu
3
O
7-δ
Dongwook Lee
1,2
· Jiwon Seo
1,3
· Luis de los Santos Valladares
1
·
Angel Bustamante Dom´ ınguez
4
· A. M. Osorio Anaya
5
· Crispin H. W. Barnes
1
Received: 31 August 2015 / Accepted: 26 September 2015 / Published online: 14 October 2015
© Springer Science+Business Media New York 2015
Abstract The AC susceptibility of [Y
0.8
Ca
0.2
](Ba
0.5
Sr
0.5
)
2
Cu
3
O
7−δ
was investigated as a function of frequency and
amplitude of AC magnetic field. The susceptibilities of
the sample display the field amplitude dependence. The
peak temperature (T
p
) of its imaginary part shows not fre-
quency dependence but field amplitude dependence. The
frequency effect on AC susceptibility was negligible. As
the field amplitude increases, T
p
shifts to lower tempera-
ture. This effect can be interpreted in terms of bulk pinning
hysteresis loss due to the vortices motion in/out grain
boundary.
Dongwook Lee
dongwookleedl324@gmail.com
Jiwon Seo
jiwonseo@yonsei.ac.kr
1
Department of Physics, University of Cambridge,
J.J. Thomson Avenue, Cambridge CB3 0HE, UK
2
Physics and Applied Physics, School of Physical
& Mathematical Sciences, Nanyang Technological
University, 637371 Singapore, Singapore
3
Department ofPhysics and IPAP, Yonsei University,
Seoul 120-749, Republic of Korea
4
Laboratorio de Cer´ amicos y Nanomateriales, Facultad
de Ciencias F´ ısicas, Universidad Nacional Mayor
de San Marcos, Ap. Postal 14-0149 Lima, Per ´ u
5
Laboratorio de Sol Gel, Facultad de Qu´ ımica e Ingenier´ ıa
Qu´ ımica, Universidad Nacional Mayor de San Marcos,
Av. Venezuela s/n, cdra 34, Ciudad Universitaria, Lima, Per´ u
Keywords [Y
0.8
Ca
0.2
](Ba
0.5
Sr
0.5
)
2
Cu
3
O
7−δ
·
AC susceptibility · Rietveld refinement
1 Introduction
Since the discovery of YBa
2
Cu
3
O
7−δ
(YBCO) [1],
research on enhancing the critical temperature (T
C
) of
YBCO has been extensively carried out by rare-earth ele-
ments and/or transition metal atoms substitutions [2, 3].
Substitution of Y
3+
by Ca
2+
increases carrier concentra-
tion and has an influence on the charge transfer from Cu–O
chains to the CuO
2
layers, which suppress the T
C
from 90
to 80 K depending on the concentration of Ca atoms [2,
3], while the substitution of Sr
3+
on the Ba site influences
mobile hole concentration by charge-transfer from CuO
2
plane, which also changes T
C
[4, 5]. In addition, study on
superconducting properties and ac loss of YBCO and one-
site doped YBCO has been enormously performed with
AC susceptibility measurements [6, 8]. AC susceptibility
(χ = χ
′
+ iχ
′′
) measurements with high T
C
superconduc-
tors have been widely used as a powerful tool to investigate
superconducting properties such as magnetization, critical
currents, order parameter, conductivity, and so on [9, 10].
The real part (χ
′
) represents transition from near-perfect
screening to complete penetration of external AC magnetic
field into the sample. The peak of the imaginary part (χ
′′
)
represents the bulk pinning hysteresis losses in the sam-
ple due to the vortices motion in/out grain boundary [11,
12]. Pinning losses are less dependent on the frequency of
the field but rely on the field amplitude, while the flux
losses depend on the frequency, not on the field ampli-
tude [13]. YBCO has frequency dependence, i.e., flux flow
motion plays an important role in its AC loss [7, 14–16]. In