Upload
omar-alejandro-salazar
View
214
Download
0
Embed Size (px)
Citation preview
8/17/2019 Specific Absorption Rate Determination of Magnetic Nanoparticles Through Hyperthermia Measurements in Non-Ad…
1/6
8/17/2019 Specific Absorption Rate Determination of Magnetic Nanoparticles Through Hyperthermia Measurements in Non-Ad…
2/6
both samples, solutions containing 10 mg/ml of particles in deio-
nised water have been prepared. Room temperature hysteresis
loops of as-received dried particles have been measured with a
LakeShore 7410 VSM: the results are reported in Fig. 1.
Sample A is constituted by larger particles, with a lower surface
to volume ratio with respect to sample P; therefore, as expected,
their saturation magnetisation is higher, and almost equal to the
saturation of bulk magnetite. Sample P, instead, is characterised by
smaller particles, with a higher surface to volume ratio leading to a
reduced saturation, that display a superparamagnetic behaviour,
with zero coercive eld and a much slower approach to saturation.
These two samples are representative of two different classes of
particles often studied for MPH applications.
3. Hyperthermia setup: calibration and modelling
The hyperthermia setup used in our experiments consists in a
water-cooled copper coil made of 4 turns, connected to a rf gen-
erator through a matching network, and able to generate elec-
tromagnetic elds with intensity up to 100 mT at a frequency of
100 kHz. Inside the coil, a PTFE sample holder hosts an Eppendorf
test tube containing 1 ml of water into which known concentra-
tions of magnetic nanoparticles are dispersed. At equilibrium and
with no rf eld applied, the sample remains at a constant tem-
perature T a¼23.5 °C thanks to the water-cooling of the coil. In
order to measure the temperature of the water solution, a type-T
(wires diameter 0.127 mm) thermocouple is available, that doesnot allow the measurement of the sample temperature during the
rf irradiation process. However, it can be inserted in the test tube
immediately after the rf eld is switched off, in order to measure
the time-dependent temperature decay of the sample towards T a.
As we will show, if a suitable calibration of the experimental setup
is available, an accurate determination of the specic absorption
rate (SAR), and consequently of intrinsic loss power (ILP), can be
obtained by just knowing the two temperatures T a and T M , the
latter being the equilibrium temperature reached by the nano-
particles solution at steady state during irradiation.
An accurate determination of SAR would require a hy-
perthermia setup operating in ideally adiabatic conditions [10,18],
i.e. a calorimeter would be the optimum choice for this kind of
measurements. However, such complex setups are often not
available and SAR is therefore determined by measuring the initial
slope of the sample temperature vs. time when the rf eld isswitched on [11]. This procedure leads to approximate results that
may be affected by how the temperature vs. time curve is analysed
and by the accuracy of the adiabatic hypothesis in the actual ex-
perimental setup, and requires suitable corrections for compen-
sating the heat exchange with the surrounding environment
[12,13].
To avoid these problems, we opted to keep simple the hy-
perthermia experiment, while taking into account the heat ex-
change of the sample with the surrounding environment in the
physical model that describes its thermodynamics. In this way,
after a suitable calibration procedure, the SAR can be accurately
measured even in non-adiabatic conditions.
The hyperthermia system can be modelled as described in
Fig. 2. A heat source S (e.g. the nanoparticles inside the solution)provides energy Q s in, to the system (e.g. through the power lossesof the magnetic particles excited by the rf eld), and exchanges
heat with the water W , Q s out , and Q w in, representing the sameamount of heat, respectively, owing out of the S subsystem and
into the W one. Finally, the water exchanges heat Q w out , with theenvironment (at temperature T a). At each instant of time, the heat
exchange equations for the S and W subsystems are the following:
δ δ δ = +
( )
Q
dt
Q
dt
Q
dt 1as s in s out , ,
δ δ δ = +
( )
Q
dt
Q
dt
Q
dt 1bw w in w out , ,
where each term is taken with its proper sign (positive for heatentering the subsystem, negative for heat released by the
subsystem).
The rst term δ Q
dt
s in, is given by the power P that is provided
through the source. The two terms δ Q dt
s out , and δ Q
dt
w in, are of opposite
sign and given by the following expression:
δ δ
τ = − = − [ ( ) − ( )]
( )
Q
dt
Q
dt
c mT t T t
2s out w in s s
ss w
, ,
where c s is the specic heat of the source, ms is its mass, τ s is the
time constant of the heat exchange process between the source
and the water, T s is the source temperature and T w is the tem-
perature of the water. Both quantities T s and T w depend on time,
but in typical hyperthermia experiments involving magnetic
Fig. 1. Room temperature hysteresis loops of sample A (blue curve) and sample P
(red curve). Inset: magnication at low elds to better show the coercivity. (For
interpretation of the references to colour in this gure caption, the reader is re-
ferred to the web version of this paper.)
Fig. 2. Thermodynamic scheme of the hyperthermia system. S is the source sub-
system (i.e. the magnetic nanoparticles). W is the water subsystem in which the
nanoparticles are dispersed. P is the exciting power. Q terms represent the heat
exchanged by the two subsystems with each other and with the environment.
M. Coïsson et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎2
Please cite this article as: M. Coïsson, et al., Journal of Magnetism and Magnetic Materials (2015), http://dx.doi.org/10.1016/j. jmmm.2015.11.044i
http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044
8/17/2019 Specific Absorption Rate Determination of Magnetic Nanoparticles Through Hyperthermia Measurements in Non-Ad…
3/6
particles only T w is accessible.
Finally, the term δ Q dt
w out , needs to be evaluated. To this purpose, a
rst calibration procedure has been carried on, consisting in put-
ting in the test tube 1 ml of water that has been pre-heated on a
hot plate. The test tube is in its sample holder and the cooling
water is let circulate in the rf coil, even though no rf eld is gen-
erated. The thermocouple logs the time dependence of the tem-
perature of water as it gradually recovers to the temperature T a of
the surrounding environment. Fig. 3 reports the results of one of the several tests that have been performed on water that has been
pre-heated at different temperatures. An exponential decay of the
temperature over time is expected. However, the experimental
data could not be tted with a single exponential function,
whereas two were required to reproduce the data. The time con-
stants of the two exponential functions turned out to be fairly
reproducible within the whole set of measurements; an average
value has then been calculated, giving rise to the nal results:
τ = 137.5 sw1 and τ = 498.1 sw2 . The presence of two time constants
indicates that the dissipation of heat towards the external en-
vironment is constituted by two mechanisms: the rst possibly
involves heat transfer through the test tube walls and sample
holder, and the second through the top surface of the liquid in the
test tube.
Therefore, it is necessary to express δ Q dt
w out , as the sum of two
terms in the form:
δ
τ τ = − [ ( ) − ] − [ ( ) − ]
( )
Q
dt
c mT t T
c mT t T
3aw out w w
ww a
w w
ww a
,
1 2
τ τ
τ τ = −
( + )[ ( ) − ]
( )
c mT t T
3bw w w w
w ww a
1 2
1 2
where c w and mw are the specic heat and mass of the water,
respectively. τ w1 and τ w2 are the time constants of the two heat
transfer mechanisms to the surrounding environment.
Therefore, Eq. (1) can be written in the following way:
δ
τ = − [ ( ) − ( )]
( )
Q
dt P
c mT t T t
4as s s
ss w
δ
τ
τ τ
τ τ = [ ( ) − ( )] −
( + )[ ( ) − ]
( )
Q
dt
c mT t T t
c mT t T
4bw s s
ss w
w w w w
w ww a
1 2
1 2
The term P appearing in Eq. (4a) is the power that is released to
the system by the source. In a typical hyperthermia experiment,
this term is the power generated by the nanoparticles that aresubmitted to the rf eld (this is not the power emitted by the rf
generator driving the coil, that is usually much higher). From the
rst principle of thermodynamics, Δ = Δ − ΔU Q L, with U being the
internal energy of the system, and Q and L the heat and work
exchanged by the system with the outside, respectively. If we as-
sume that in the studied temperature range the water does not
appreciably change its volume, then Δ =L 0. The internal energy of
both subsystems S and W can then be expressed in terms of
temperature through the expressions =Δ
Δ c m
Q
T s w s w, ,s w
s w
,
,. As a con-
sequence, the thermodynamic behaviour of the hyperthermia
setup can be modelled with the following set of coupled differ-
ential equations:
τ − [ ( ) − ( )] =
( )
( )P
c m
T t T t c m
dT t
dt 5as s
ss w s s
s
τ
τ τ
τ τ [ ( ) − ( )] −
( + )[ ( ) − ]
= ( )
( )
c mT t T t
c mT t T
c m dT t
dt 5b
s s
ss w
w w w w
w ww a
w ww
1 2
1 2
In order to solve the system (5) for the two unknowns T s(t ) and
T w(t ), values for c s, ms and τ s should be provided. Instead, c w is
known (4187 J kg1 K1), as well as mw, since the amount of water
put in the test tube can be measured. However, the specic heat,
mass and time constant of the source are not easily determined for
a typical hyperthermia sample consisting on magnetic nano-
particles. Therefore, we performed a second calibration step where
the source term is replaced by a known resistor having a small sizeand a value of 10.2 Ω. When a known current of constant intensityis let pass through the resistor, it produces a known power =P RI 2
that is used to heat the water. This is also the power term that
enters Eq. (4a) and following. To simplify the system and ease the
calibration process, the resistor has been immersed in a solution of
water and ice, that is therefore at temperature ≈ °T 0 Cice ; this
temperature will not change when the resistor heats up due to the
current that ows through it, leading to a much simplied ther-
modynamic description of the system. The thermocouple has been
placed in direct contact with the resistor, in order to measure its
temperature as it heats up when the current ows through it. In
this way, the system (5) reduces to a single equation with the
temperature of the source (resistor) being the only unknown:
τ
( )= − [ ( ) − ]
( )c m dT t
dt P c m T t T
6s s
s s s
ss ice
where the quantities with suf x s now refer to the resistor that
acts as heat source in this particular case. Eq. (6) can be rearranged
as:
τ τ
( )= − ( ) + +
( )
⎡
⎣⎢
⎤
⎦⎥
dT t
dt T t
P
c m
T 1
7
s
ss
s s
ice
s
that is in the form ′ = − y ay b that, for the initial condition
( ) = y y0 0, has the analytical solution = + [ − ] y y eb
a
b
aat
0 . Therefore,
Eq. (6) can be solved as:
τ ( ) = + [ − ]
( )
τ −T t T P
c m
e1
8
s ices
s s
t / s
0 500 1000 1500 200020
25
30
35
40
45
time (s)
experimental data
Fig. 3. Symbols: time dependence of the temperature of 1 ml of pre-heated watercooling down in the hyperthermia setup. Red line: tting with the sum of two
exponential functions. (For interpretation of the references to colour in this gure
caption, the reader is referred to the web version of this paper.)
M. Coïsson et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎ ∎∎–∎∎∎ 3
Please cite this article as: M. Coïsson, et al., Journal of Magnetism and Magnetic Materials (2015), http://dx.doi.org/10.1016/j. jmmm.2015.11.044i
http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044
8/17/2019 Specific Absorption Rate Determination of Magnetic Nanoparticles Through Hyperthermia Measurements in Non-Ad…
4/6
for the initial condition ( ) =T T 0s ice. The experimental results of the
time dependence of the temperature of the resistor immersed in
water and ice for a value of P ¼0.41 W are reported in Fig. 4, that is
representative of the several measurements that have been per-
formed with different heating powers up to E1 W (higher powers
would have led to an excessive temperature increase of the water,
well beyond the range that is interesting for MPH applications).
The data reported in Fig. 4, as well as all the other available
data, have been tted with Eq. (8) leaving τ s and the product c ms sas free parameters. The obtained values have been averaged and
the nal results have been obtained: τ = 89.0 ss and =c m 7.0 J/Ks s .
We will assume that these values describe the properties of the
resistor when it exchanges heat with water, both in the conditions
exploited for calibration purposes and in an actual hyperthermia
experiment represented in Fig. 2 and modelled by Eq. (5), when
the water will effectively heat up.
It is therefore now possible to validate the thermodynamic
model by performing a measurement of the temperature of the
water in the test tube in its sample holder with the cooling water
circulating in the rf coil but without the rf eld, as the heat source
will be the power provided by the calibration resistor. In practice,
an experiment in the same conditions as a normal hyperthermia
measurement is performed, with the difference that the heatsource is not the magnetic nanoparticles excited by the rf eld, but
the calibration resistor that heats the water by means of the Joule
effect with a known power. Since the rf eld is off, in this case it is
possible to use the thermocouple to measure T w(t ) during both
heating and cooling. The results, for heating powers of 0.41 W and
0.10 W (taken as examples) applied for 7200 s and 1800 s, re-
spectively, are reported in Fig. 5 (black symbols).
Eq. (5) is solved numerically using the values for c ms s, τ s, τ w1and τ w2 obtained in the two calibration steps, and with a volume
of 0.7 ml (mw¼0.7 g) of water. The solutions, calculated for the
same heating powers and heating times adopted in the experi-
ment, are plotted in Fig. 5 as the green lines. The agreement with
the experimental results is excellent. It is important to point out
that no free parameter has been adjusted to obtain this
agreement: all the quantities involved in Eq. (5) have been either
measured during the two calibration processes (time constants of
the heat transfer process from the test tube to the environment,
heat capacity of the calibration resistor, time constant of the heat
transfer process from the calibration resistor to water, power), or
are otherwise known (volume of water, its specic heat).
As a result, we can therefore consider the system of (5) as an
adequate thermodynamic representation of our hyperthermia
setup. We can then exploit them to determine the SAR of an un-
known source (magnetic nanoparticles). If the system is brought to
thermal equilibrium during the heating process, the energy en-
tering the system through the rf eld exciting the nanoparticles
and the energy released to the environment are equal and oppo-
site in sign; as a consequence, both ( )dT t dt s and ( )dT t
dt w are equal to
zero. Therefore, from Eq. (5):
τ τ
τ τ =
( + )[ − ]
( )P
c mT T
9w w w w
w wM a
1 2
1 2
where T M is the maximum (equilibrium) temperature reached
during the heating process. With this approach, it is not necessary
to measure the temperature of the water during the heating pro-
cess and to correct its time derivative for the residual heat ex-
change with the surrounding environment. Instead, it is suf cient
to know T M , that can be measured in stationary conditions with an
optical thermometer or immediately after the rf eld is switched
off with just a thermocouple, to determine P , as all the other
quantities entering Eq. (9) are now known and the model Eq. (9)
belongs to has been validated. With P obtained in this way, by
knowing the mass of particles used in the experiment, their spe-
cic absorption rate is obtained accurately for the given rf eld
intensity and frequency.
4. SAR measurements on magnetic nanoparticles
Magnetic hyperthermia has been measured on both samples A
0 100 200 300 400 500 6000
2
4
6
8
10
t (s)
experimental data
thermodynamic model
s> = 89.0 s
= 7 J / K
<
Fig. 4. Symbols: time dependence of the temperature of the calibration resistor
immersed in iced water when an electrical current ows through it giving a heating
power of 0.41 W. Blue line: tting with Eq. (8) with τ s and the product c ms s left as
free parameters. (For interpretation of the references to colour in this gure cap-
tion, the reader is referred to the web version of this paper.)
0 2 4 6 8 1020
25
30
35
40
t (103 s)
experimental data
thermodynamic model
P = 0.41 W
P = 0.10 W
Fig. 5. Symbols: time dependence of the temperature of the water heated by
means of the calibration resistor with a power of 0.41 W. and 0.10 W. Green lines:
numerical solutions of Eq. (5) with the values obtained in the course of the two
calibration processes, for the same heating powers. (For interpretation of the re-
ferences to colour in this gure caption, the reader is referred to the web version of
this paper.)
M. Coïsson et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎4
Please cite this article as: M. Coïsson, et al., Journal of Magnetism and Magnetic Materials (2015), http://dx.doi.org/10.1016/j. jmmm.2015.11.044i
http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044
8/17/2019 Specific Absorption Rate Determination of Magnetic Nanoparticles Through Hyperthermia Measurements in Non-Ad…
5/6
and P under three different values of rf eld (30, 60, and 90 mT)
applied for 1800 s. According to our preliminary investigations,
carried on by performing several measurements at different
heating times, 1800 s are suf cient to reach the equilibrium stable
state. The thermocouple is inserted in the test tube immediately
after switching off the rf eld, therefore the rst measured tem-
perature is assumed to be equal to T M . The samples are then left
cool down to T a. Fig. 6 shows the three temperature vs. time curvesfor both samples A and P; for convenience, the abscissa is relative
to the switching on of the rf eld; as only the cooling part of the
curve is acquired, the horizontal axis in Fig. 6 starts at 1800 s.
The equilibrium temperatures T M for the three applied rf eld
intensities are shown in the inset: as expected, the system heats at
higher temperatures when higher rf elds are applied. With the
measured values of T M for both samples A and P it is then possible
to calculate SAR using Eq. (9):
=( )
SAR P
m 10 particles
where m particles is the mass of the particles dispersed in the solu-
tion. The results are reported in Fig. 7a. As expected, SAR increases
with increasing eld value; for rf elds below 30 mT the power
losses of the studied particles become negligible.
However, the intrinsic loss power (ILP) has been proposed as a
quantity more suitable for comparing hyperthermia results ob-
tained on different families of particles, since the power losses are
normalised not only to the sample mass, but also to eld intensity
and frequency [19]:
ν=
( )ILP
SAR
H 112
where ν is the frequency of the rf exciting eld H . In Fig. 7b values of
intrinsic loss power are reported for both samples A and P. A cleardistinction between the two samples can be observed: sample A,
which is constituted by larger particles that display static hysteresis
(see Fig. 1), has a non-monotonous dependence of ILP with the rf
eld, indicating non-linear magnetisation dynamics giving rise to
power losses that depend on eld intensity. Conversely, sample P,
that is constituted by smaller particles having a superparamagnetic
behaviour, is characterised by an almost constant ILP as a function
of H , having a lower value with respect to sample A.
5. Conclusions
A thermodynamic model and a calibration procedure have been
proposed for a magnetic hyperthermia setup that does not need to
Fig. 6. Time dependence of the temperature of 1 ml of water containing 10 mg of
particles of samples A (top) and P (bottom), submitted to three values of rf eld for
1800 s. The origin of the abscissa is at the instant of switching on of the rf eld.
Insets: dependence of the equilibrium temperature T M as a function of the rf eld
intensity.
Fig. 7. Specic absorption rate (SAR, panel (a)) and intrinsic loss power (ILP, panel
(b)) as a function of rf exciting eld of samples A and P.
M. Coïsson et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎ ∎∎–∎∎∎ 5
Please cite this article as: M. Coïsson, et al., Journal of Magnetism and Magnetic Materials (2015), http://dx.doi.org/10.1016/j. jmmm.2015.11.044i
http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044
8/17/2019 Specific Absorption Rate Determination of Magnetic Nanoparticles Through Hyperthermia Measurements in Non-Ad…
6/6
operate in adiabatic conditions. Accurate determination of the
specic absorption rate is possible without measuring the initial
slope of the temperature vs. time curve; instead, by measuring the
equilibrium temperature at the stationary state, SAR can be ob-
tained. The thermodynamic model is validated on the actual ex-
perimental setup through a proper calibration procedure, and the
method is nally applied on a set of samples consisting in water
solutions of magnetic nanoparticles allowing the experimental
determination of SAR and ILP.
References
[1] S. Dutz, R. Hergt, Nanotechnology 25 (2014) 452001.[2] M. Latorre, C. Rinaldi, P. R. Health Sci. J. 28 (2009) 227 .[3] C.S.S.R. Kumar, F. Mohammad, Adv. Drug Deliv. Rev. 63 (2011) 789.[4] Nguyen T.K. Thanh (Ed.), Magnetic Nanoparticles from Fabrication to Clinical
Application, CRC Press, Taylor & Francis Group, FL, USA, 2012.[5] A. Figuerola, R. Di Corato, L. Manna, T. Pellegrino, Pharmacol. Res. 62 (2010)
126.[6] J. van der Zee, Ann. Oncol. 13 (2002) 1173 .[7] F. Cardoso, A. Costa, L. Norton, E. Senkus, M. Aapro, F. André, C.H. Barrios,
J. Bergh, L. Biganzoli, K.L. Blackwell, M.J. Cardoso, T. Cufer, N. El Saghir,L. Falloweld, D. Fenech, P. Francis, K. Gelmon, S.H. Giordano, J. Gligorov,A. Goldhirsch, N. Harbeck, N. Houssami, C. Hudis, B. Kaufman, I. Krop,
S. Kyriakides, U.N. Lin, M. Mayer, S.D. Merjaver, E.B. Nordström, O. Pagani,
A. Partridge, F. Penault-Llorca, M.J. Piccart, H. Rugo, G. Sledge, C. Thomssen,
L. vant Veer, D. Vorobiof, C. Vrieling, N. West, B. Xu, E. Winer, Ann. Oncol.
(2014) 1.[8] R. Hergt, S. Dutz, R. Müller, M. Zeisberger, J. Phys.: Condens. Matter 18 (2006)
S2919.[9] A.E. Deatsch, B.A. Evans, J. Magn. Magn. Mater. 354 (2014) 163 .
[10] E. Natividad, M. Castro, A. Mediano, J. Magn. Magn. Mater. 321 (2009) 1497.[11] R. Di Corato, A. Espinosa, L. Lartigue, M. Tharaud, S. Chat, T. Pellegrino,
C. Ménager, F. Gazeau, C. Wilhelm, Biomaterials 35 (2014) 6400.[12] K. Simeonidis, C. Martinez-Boubeta, Ll. Balcells, C. Monty, G. Stavropoulos,
M. Mitrakas, A. Matsakidou, G. Vourlias, M. Angelakeris, J. Appl. Phys. 114
(2013) 103904.[13] D. Sakellari, K. Brintakis, A. Kostopoulou, E. Myrovali, K. Simeonidis, A. Lappas,
M. Angelakersi, Mater. Sci. Eng. C 58 (2016) 187.[14] X.L. Liu, Y. Yang, C.T. Ng, L.Y. Zhao, Y. Zhang, B.H. Bay, H.M. Fan, J. Ding, Adv.
Mater. 27 (2015) 1939.[15] E.A. Rozhkova, V. Novosad, D.-H. Kim, J. Pearson, R. Divan, T. Rajh, S.D. Bader, J.
Appl. Phys. 105 (2009) 07B306.[16] D.-H. Kim, E.A. Rozhkova, I.V. Ulasov, S.D. Bader, T. Rajh, M.S. Lesniak,
V. Novosad, Nat. Mater. 9 (2010) 165 .[17] P. Tiberto, G. Barrera, F. Celegato, G. Conta, M. Coisson, F. Vinai, F. Albertini, J.
Appl. Phys. 117 (2015) 17B304.[18] A. Chalkidou, K. Simeonidis, M. Angelakeris, T. Samaras, C. Martinez-Boubeta,
Ll. Balcells, K. Papazisis, C. Dendrinou-Samara, O. Kalogirou, J. Magn. Magn.
Mater. 323 (2011) 775.[19] M. Kallumadil, M. Tada, T. Nakagawa, M. Abe, P. Southern, Q.A. Pankhurst, J.
Magn. Magn. Mater. 321 (2009) 1509.
M. Coïsson et al. / Journal of Magnetism and Magnetic Materials ∎ (∎∎∎∎) ∎∎∎–∎∎∎6
Please cite this article as: M. Coïsson, et al., Journal of Magnetism and Magnetic Materials (2015), http://dx.doi.org/10.1016/j. jmmm.2015.11.044i
http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref1http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref1http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref2http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref2http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref3http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref3http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref5http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref5http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref5http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref6http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref6http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref8http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref8http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref8http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref9http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref9http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref10http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref10http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref11http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref11http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref11http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref12http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref12http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref12http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref12http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref13http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref13http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref13http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref14http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref14http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref14http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref15http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref15http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref15http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref16http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref16http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref16http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref17http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref17http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref17http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref18http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref18http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref18http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref18http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref19http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref19http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref19http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://dx.doi.org/10.1016/j.jmmm.2015.11.044http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref19http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref19http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref18http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref18http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref18http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref17http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref17http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref16http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref16http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref15http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref15http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref14http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref14http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref13http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref13http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref12http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref12http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref12http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref11http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref11http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref10http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref9http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref8http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref8http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref7http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref6http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref5http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref5http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref3http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref2http://refhub.elsevier.com/S0304-8853(15)30815-5/sbref1