Magne o-mechanical beha io in polyu e hane oams con aining o ien ed
FeCo mic opa icles: A compe i ion be ween bending and s e ching e ec s
A. Lashe as
a,*
, J. G´
omez-Hu ado
a,b
, J.M. Laza
b
, J. Be asa egi
c
, M.M. Bou-Ali
c
,
J. Gu ie ´
ez
d
, J.L. Vilas-Vilela
b,e
, Ana Ca a ina Lopes
b, ,**
a
Dep . o Physics, Science and Technology Facul y, Uni e si y o he Basque Coun y (UPV/EHU), Leioa 48940, Spain
b
Mac omolecula Chemis y G oup (LABQUIMAC), Depa men o Physical Chemis y, Facul y o Science and Technology, Uni e si y o he Basque Coun y (UPV/
EHU), Leioa 48940, Spain
c
Mechanical and Indus ial P oduc ion Depa men , Facul y o Enginee ing, Mond agon Uni e si y, A asa e, Mond agon, Spain
d
Dp . Elec ici y and Elec onics, Science and Technology Facul y, Uni e si y o he Basque Coun y (UPV/EHU), Leioa 48940, Spain
e
BCMa e ials, Basque Cen e o Ma e ials, Applica ions and Nanos uc u es, Leioa 48940, Spain
IKERBASQUE, Basque Founda ion o Science, Plaza Euskadi 5, Bilbao 48009, Spain
ARTICLE INFO
Key wo ds:
Polyu e hane Foam
So composi es
FeCo mic opa icles
Magne os ic ion
Magne o-mechanical beha io
ABSTRACT
So magne o-ac i e composi es a e o pa icula in e es in a eas o biomedical applica ions, wea able senso s
and so obo ic. In his con ex , his wo k p esen s a deep s udy o how he inco po a ion o Fe₇₀Co₃₀ mic o-
pa icles in o oam polyu e hane composi es a ec s i s magne os ic i e esponse. The composi es we e ab i-
ca ed in bo h oam and oam ilm-like s uc u es, esul ing om ee o con ined expansion, espec i ely, and
wi h a ying pe cen ages and o ien a ions o magne ic mic opa icles. All o he ab ica ed oams ha e been
op ically, magne ically, mechanically and he mally cha ac e ized. The inclusion o magne ic mic opa icles had
negligible impac on he mal s abili y and deg ada ion beha io . In con as , mechanical and magne ic p op-
e ies we e highly sensi i e o bo h he concen a ion and alignmen o he pa icles. Magne os ic ion beha io
e ealed a compe i ion be ween bending and s e ching mechanisms, go e ned by he composi e’s s i ness. A
lowe pa icle con en s (≤40 w %), bending domina ed, p oducing nega i e magne os ic ion alues. As pa icle
con en inc eased (>40 w %), he ma e ial s i ened, supp essing bending and allowing s e ching o p e ail,
esul ing in posi i e magne os ic ion, pa icula ly e iden in oam- ilm composi es. These indings demons a e
he unabili y o he magne ic esponse in so composi es h ough s uc u al and composi ional con ol.
1. In oduc ion
The de elopmen o magne o-ac i e ma e ials has expe ienced a
huge g ow h in he las yea s due o hei ele ance in a eas such as
indus ial au oma ion, ag icul u e, and medical obo ics[1,2]. Pa icu-
la ly in e es ing a e he so magne o-ac i e ma e ials, which ha e been
ecen ly employed in biomedical applica ions, wea able senso s and so
obo ics, among o he s[3]. Those a e composed o a so polyme ic
ma ix, such as so elas ome s o hyd ogels, combined wi h dispe sed
magne ic mic o o nanopa icles. These ma e ials a e able o gene a e
la ge mechanical de o ma ion unde he applica ion o an ex e nal
magne ic ield, p o iding a emo e esponse and allowing e e sible and
complex de o ma ions.
In he pa icula case o elas ome s, hei mechanical so ness en-
ables a e e sible de o ma ion, allowing a shape mo phing e ec .
Among he mos employed elas ome s a e silicones[4], ac yla e-based
polyme s[5] and polyu e hanes[6]. Rega ding he magne ic ille ,
NdFeB pa icles[7] and oxides such as Fe
3
O
4
[8] o C O
2
[9] ha e been
al eady used.
Mos o he esea ch in so magne o-ac i e composi es has been
de o ed o imp o e hei magne o heological esponse, mainly by
modi ying he olume, size and dis ibu ion o he illed pa icles[10].
Howe e , he magne os ic i e e ec in hese ma e ials has no been
deeply analysed. Some s udies ha e epo ed he impo ance o he
* Co esponding au ho .
** Co esponding au ho a : Mac omolecula Chemis y G oup (LABQUIMAC), Depa men o Physical Chemis y, Facul y o Science and Technology, Uni e si y o
he Basque Coun y (UPV/EHU), Leioa 48940, Spain.
E-mail add esses: [email p o ec ed] (A. Lashe as), [email p o ec ed] (A.C. Lopes).
Con en s lis s a ailable a ScienceDi ec
Senso s and Ac ua o s: A. Physical
jou nal homepage: www.jou nals.else ie .com/senso s-and-ac ua o s-a-physical
h ps://doi.o g/10.1016/j.sna.2025.116949
Recei ed 29 May 2025; Recei ed in e ised o m 24 July 2025; Accep ed 7 Augus 2025
Senso s & Ac ua o s: A. Physical 394 (2025) 116949
A ailable online 13 Augus 2025
0924-4247/© 2025 The Au ho s. Published by Else ie B.V. This is an open access a icle unde he CC BY-NC license ( h p://c ea i ecommons.o g/licenses/by-
nc/4.0/ ).
pa icles’ shape and size o op imizing he mechanical de o ma ion
[11–13]. In he same way, o he wo ks ha e paid a en ion o he e ec
o he pa icles alignmen in he polyme ic ma ix[14], bu wi hou
p o iding a ull s udy. Mo e ecen ly, Sil a e al. epo ed a gian
magne os ic i e e ec in low-concen a ion iso opic and aniso opic
FeCo–2 V helicoidal pa icles combined wi h he polydime hylsiloxane
so elas ome ma ix[15].
These magne o-ac i e composi es a e usually ab ica ed in a
con inuous ma ix, commonly a silicone s uc u e[16,17]. Howe e , due
o he need o ind ligh weigh ed low-densi y sma ma e ials, he po-
en ial o polyme composi es in he o m o oams has begun o be
ecognized and s udied, coun e ac ing he high densi y o monoli hic
ma e ials[18]. The po osi y in magne o-ac i e composi es educes he
e ec i e Young’s modulus, making he inal s uc u e so e [19,20].
Magne ic oams ha e been al eady used in se e al applica ion such as
mic owa e abso p ion composi es [21] o ene gy gene a ing sys ems
[22]. Among he ma ixes used in oams, he polyu e hane is he mos
common one[23–25], due o i s good shape memo y as well as high
ene gy and shock abso p ion p ope ies[26]. The magne os ic i e
cha ac e is ics o polyu e hane oams illed wi h magne ic pa icles,
such as ca bonyl i on pa icles (CIP)[27], ha e been p e iously in es-
iga ed. Howe e , he in luence o pa icle o ien a ion on he magne-
os ic i e p ope ies o hese s uc u es has ecei ed ela i e li le
a en ion. Mos exis ing s udies ha e p ima ily ocused on hei mag-
ne o heological beha iou , howe e , some s udies ha e al eady shown
ha s uc u es wi h aniso opies can exhibi di e en esponses
depending on he o ien a ion o he magne ic ield [28]. Explo ing he
magne os ic i e e ec in oam-like s uc u es could e eal new insigh s
in o he ma e ial’s beha io unde magne ic ields, which is c ucial o
op imizing hei pe o mance in a ious applica ions.
By in es iga ing how he o ien a ion o he pa icles in luences he
magne ically induced de o ma ion in hese po ous ma e ials, we can
enhance he design o ad anced composi es wi h ailo ed unc ional-
i ies. Such ma e ials could be pi o al in de eloping nex -gene a ion
senso s, ac ua o s, and sma hyb id ma e ials, expanding he po en-
ial o magne os ic i e echnologies in indus ial and echnological
domains.
In his wo k, magne o-ac i e composi es o med by high-
magne iza ion Fe
70
Co
30
mic opa icles embedded in a polyu e hane
ma ix a e in es iga ed in a oam-like s uc u e. In o de o ha e a
b oade unde s anding o he magne ic, mechanical, and s uc u al
p ope ies in he composi es, we ha e explo ed wo di e en ou es o
hei ab ica ion. In he i s app oach, he oam-like s uc u e wi h
magne ic pa icles has been eely g own, o ming a magne ic oam-like
composi e. In a second app oach, he composi e has been ab ica ed in a
es ic ed olume, a oiding he ee expansion o he oam, leading o a
comp essed magne ic oam ilm-like composi e. These wo dis inc
me hodologies will enable us o assess he in luence o s uc u al
con inemen and shape on he composi e’s o e all pe o mance, o e ing
aluable insigh s in o hei po en ial applica ions in lexible,
magne ically- esponsi e de ices. The p ope ies o he ab ica ed com-
posi es ha e been analysed as a unc ion o he pa icle con en pe -
cen age, as well as a unc ion o hei ela i e o ien a ion. We ha e
obse ed a compe i ion be ween bending and s e ching e ec s in he
ma e ial when pa icles a emp o align wi h he magne ic ield. This
esul s in bo h nega i e and posi i e alues o magne os ic ion, is being
highly dependen on he mechanical p ope ies o he ma e ial. These
p ope ies, in u n, a ise om a ying concen a ions and o ien a ions o
he magne ic Fe₇₀Co₃₀ mic opa icles. We belie e ha hese indings
unde sco e he c i ical ole o pa icle o ien a ion and pe cen age in
ailo ing he magne os ic i e esponse o oam-like composi es. This
unde s anding opens up new pe spec i es o designing and op imizing
oam-based magne o-ac i e ma e ials o a ange o applica ions, om
senso s and ac ua o s o adap i e s uc u al componen s.
2. Expe imen al sec ion
2.1. Ma e ials
The polyu e hane based magne ic oam composi es we e p epa ed
by using he comme cial polyu e hane oam Poly oam F3, pu chased
om Fe oca-Poly ek.
Magne ic me allic mic opa icles o composi ion Fe
70
Co
30
we e
syn hesized by using he gas-a omiza ion echnique. The FeCo alloy
shows he highes known magne iza ion alues in he Fe- ich egion [28,
29], and as i will be u he discussed, he Fe
70
Co
30
mic opa icles used
in his wo k show a sa u a ion magne iza ion alue o 230 Am
2
/kg. Due
o he ab ica ion p ocess, hese mic opa icles show a nice, almos
pe ec sphe ical mo phology. Scanning elec on mic oscopy (SEM,
Hi achi TM3000) images o hese mic opa icles a e ep esen ed in Fig 1
(a) and (b), as well as he es ima ed size dis ibu ion in Fig. 1(c).
2.2. P epa a ion o composi es
The nea oam was p epa ed as ins uc ed by he manu ac u e . The
polyol and isocyana e componen s we e mixed in a 2:1 a io. A o al o
1.5 g o ma e ial was p epa ed o he a ious es s, consis ing o 1 g o
polyol and 0.5 g o isocyana e. The magne ic composi es we e p epa ed
in he same way, bu wi h he addi ion o he co esponding amoun o
Fe
70
Co
30
mic opa icles o he polyol componen o achie e 15, 30, 40,
50 and 65 %w o mic opa icles con en . The maximum mic opa icle
con en was es ablished by he poin a which he dis ibu ion o
mic opa icle lines became non-uni o m, wi h isible agglome a ion
occu ing a highe concen a ions, as will be discussed la e .
The composi es we e p epa ed using wo di e en ou es:
1. Foam-like s uc u e (MF: magne ic oam). This s uc u e was
ob ained by mixing bo h componen s in a glass ial, allowing he
oam o expand eely in he e ical di ec ion. Fo he p epa a ion o
magne ic composi e samples, he co esponding amoun o Fe
70
Co
30
Fig. 1. SEM images o Fe
70
Co
30
mic opa icles (a and b) and hei size dis ibu ion (c).
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
2
mic opa icles was p e-mixed wi h he poliol componen . Fo com-
posi es wi h o ien ed pa icles, he ial was p omp ly placed inside
he poles gap o an elec omagne , which gene a ed a 0.5 T magne ic
ield in he ans e se di ec ion o he ial, as shown in Fig. 2(a). This
magne ic ield in ensi y was es ed be o ehand and ound su icien
o ensu e nanopa icle alignmen du ing oam composi e o ma ion.
Fo non-o ien ed composi es, he applica ion o he ex e nal mag-
ne ic ield was emo ed. A e 10 min, he ial was b oken o ex ac
he composi e. Some o he ob ained ma e ials a e shown in Fig. 2(b).
Once he composi e is ex ac ed, di e en o ien a ions a e ob ained
by cu ing he cylind ical s uc u e along di e en planes: a ans e se
cu h ough he cen e o he cylinde and a longi udinal cu along i s
leng h. These cu s will be used o s udy he e ec o he magne ic ield on
he samples applied wi h di e en o ien a ions. This p ocedu e is
g aphically desc ibed in Fig. 3. The cu ing di ec ion had no impac on
he andomly o ien ed pa icles (O 0). Fig. 3(b) illus a es he coo di-
na e sys em used o de ine o ien a ions o pa icles. As an example, O 1
is aligned wi h (0, 0, 1), O 2 wi h (0, 1, 0) and O 3 wi h (1, 0, 0).Table 1
summa izes he p epa ed composi es, along wi h he co esponding
quan i ies o Fe
70
Co
30
mic opa icles.
2. Foam Film-like s uc u e (MFF: magne ic oam ilm). Fo his
second s uc u e, he polyol and he app op ia e amoun o mic o-
pa icles we e added o a beake and manually mixed wi h a spa ula,
ollowed by he addi ion o isocyana e. The mix u e was hen pou ed
in o a Te lon-coa ed mold, co e ed wi h a Te lon shee , and sand-
wiched be ween wo non-magne ic me al pla es. Tha is, in his se up
Fig. 2. Diag am o he employed p ocedu e o ab ica e he oam-like s uc u e (a). Pic u e o oam-like composi es wi h 0, 40 and 65 %w o Fe
70
Co
30
mic o-
pa icles (b).
Fig. 3. Diag am o he cu ing planes used o ob ain he di e en sample o ien a ions o MF (a). Scheme o he e e ence coo dina e sys em (b).
Table 1
Summa y o all he MFs ab ica ed wi h polyu e hane ma ix and Fe
70
Co
30
mic opa icles.
Sample % w o Fe
70
Co
30
O ien a ion o Fe
70
Co
30
MF
0 %
o 0 0 -
MF
10 %
o 1 10
O 1
MF
30 %
o 1 30
MF
40 %
o 1 40
MF
50 %
o 1 50
MF
65 %
o 1 65
MF
65 %
o 0 40 O 0
MF
40 %
o 2 40 O 2
MF
40 %
o 3 40 O 3
Fig. 4. Diag am o he employed p ocedu e o ab ica e he po ous polyme ilm (a). Pic u e o oam ilm-like composi es wi h 40 %w o Fe
70
Co
30
mic opa icles (b).
Table 2
Summa y o he po ous polyme ilms ab ica ed wi h polyu e hane ma ix and
Fe
70
Co
30
mic opa icles.
Sample % w o Fe
70
Co
30
O ien a ion o Fe
70
Co
30
MFF
0 %
o 0 40 O 0
MFF
10 %
o 1 10
O 1
MFF
30 %
o 1 30
MFF
40 %
o 1 40
MFF
50 %
o 1 50
MFF
65 %
o 1 65
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
3
he ma e ial was con ined and did no expand eely. The s uc u e
was placed on a magne gene a ing a pe pendicula ( o he ilm
plane) 0.45 T ield, and a non-magne ic weigh was placed on he op
o main ain p essu e and p e en he ma e ial om expanding. A
non-magne ic weigh o app oxima ely 5 kg was used, which was
su icien o apply he necessa y p essu e o p e en he ma e ial
om expanding and o ensu e i con o med o he hickness o he
Te lon mold. This p ocedu e is g aphically desc ibed in Fig. 4. A e
10 min, he composi e was emo ed om he mold. In Table 2, he
p epa ed MFF composi es a e summa ized, along wi h he co e-
sponding quan i ies o Fe
70
Co
30
mic opa icles.
2.3. Cha ac e iza ion
A e he ab ica ion o he composi es, hey we e op ically,
magne ically, mechanically and he mally cha ac e ized by using scan-
ning elec on mic oscopy, hys e esis loop and magne os ic ion mea-
su emen s, mechanical es s and he mog a ime ic analysis,
espec i ely.
To s udy he mo phology o he samples, scanning elec on mic o-
scopy (SEM, JEOL JSM-7000F) was pe o med using an accele a ing
ol age o 5 kV. The samples we e ac u ed a e imme sion in liquid
ni ogen o c oss-sec ional analysis.
A SDT Q600 (TA-Ins umen s) he mobalance was employed o
e alua e he he mal s abili y o he p epa ed composi es wi h a ying
concen a ions o magne ic mic opa icles. The mog a ime ic analysis
(TGA) was ca ied ou unde ni ogen a mosphe e and hea ing up om
25 o 800 ◦C a a a e o 10 ◦C ⋅min
−1
. The ini ial deg ada ion empe -
a u e (Ti) was de e mined a he poin whe e he mass loss eached 2 w
%, while he maximum deg ada ion empe a u e (Td) o each deg a-
da ion phase was de i ed om he minimum o he i s de i a i e
cu es. TGA expe imen s we e conduc ed in duplica e.
Comp ession es s (Me o ec FTM-50) we e ca ied ou by employing
a 20 N cell a oom empe a u e wi h a speed o 0.5 mm/min. Samples
we e p epa ed wi h an ini ial hickness o 5 mm and a diame e o
1.2 cm. The Young’s modulus was calcula ed by linea eg ession om
he slope o he s ess-s ain cu es in he linea de o ma ion zone and
he pla eau s ess om he s ess alue in he plas ic egion.
Room- empe a u e M(H) hys e esis loop measu emen s we e ca ied
ou using a ib a ing sample magne ome e (VSM), wi h an applied
ex e nal magne ic ield anging be ween −1.7 and 1.7 T. Magne o-
s ic ion measu emen s λ(H) we e pe o med by using ec angle shaped
s ain gauges wi h a gauge ac o o 2.075 and a esis ance o 120 Ω.
These we e connec ed o a Whea s one b idge wo king in hal -b idge
con igu a ion, and including a passi e gauge as e e ence. The s ain
gauges we e glued on he composi es using a M-Bond 600 adhesi e
(pu chased om Mic o-Measu emen s).
Dynamic Mechanical The mal Analysis (DMTA) was pe o med in
bending mode on a DMA 1 om Me le Toledo. Magne ic oam ilms
(MFF), wi h samples dimensions app oxima ely 1 mm hick, 5 mm wide
and 30 mm long, we e measu ed using he dual can ile e clamp.
Magne ic oams (MF), wi h samples dimensions app oxima ely 4 mm
hick, 6 mm wide and 20 mm long, we e measu ed using he single
can ile e clamp. Bo h measu emen s we e pe o med a oom em-
pe a u e (25◦C) and 1 Hz equency measu ing he o ce necessa y o
de o m he sample 900 µm (in s eps o 10 µm).
3. Resul s and discussion
3.1. Magne ic oam (MF)
As p e iously men ioned, di e en MF composi es we e p epa ed
wi h di e en pe cen ages o mic opa icles and o ien a ions. The ob-
ained composi es we e i s ly cha ac e ized in e ms o hei
mo phology. Fig. 5 shows samples o he ab ica ed MF wi h di e en
pe cen ages o Fe₇₀Co₃₀ magne ic pa icles, p epa ed unde he appli-
ca ion o a magne ic ield. The ci cula disks shown in Fig. 5(a) esul
om a ans e se cu h ough he cen e o he cylind ical ma e ial,
which co espond o he planes used o s udy he e ec o he applied
Fig. 5. View o o ien ed MF composi es o 0, 10, 30, 40, 50 and 65 % w
con en o Fe
70
Co
30
(a), and SEM images o he composi es wi h 0, 40 and 65 %
w o Fe
70
Co
30
mic opa icles (b, c and d, espec i ely). All SEM images a e
shown a he same scale.
Fig. 6. TGA measu emen s o he MF composi es o di e en Fe
70
Co
30
con en (a). Table wi h ini ial deg ada ion empe a u e (T
i
) and empe a u e a he maximum
weigh loss a e (T
d
) alues o he oams, along wi h esidual weigh pe cen ages. (b).
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
4
magne ic ield in o ien a ions O 2 and O 3.
As i can be obse ed, he pa icle o ien a ion p ocess was success ul,
as he magne ic mic opa icles lines a e clea ly iden i ied, e en o he
naked eye. The o ien a ion was con i med h ough SEM analysis, wi h
images o composi es con aining 40 and 65 % w o mic opa icles
shown in Fig. 5(c) and (d), espec i ely. Howe e , i can be also
app ecia ed he agg ega ion o he mic opa icle chains o he 65 % w
con en , which is no obse ed a lowe pe cen ages. This agg ega ion
could impac he ma e ial’s pe o mance.
Fu he , he ma e ials we e cha ac e ized ega ding o hei deg a-
da ion empe a u es. The he mal cha ac e iza ion o he composi es
was pe o med h ough TGA measu emen s o he MF wi h di e en
pe cen ages o magne ic mic opa icles. The esul s a e shown in Fig. 6.
The he mog a ime ic analysis e eals wo p ima y s ages o mass
loss, associa ed wi h deg ada ion p ocesses: he i s occu s be ween
290◦C and 310◦C, and he second, akes place be ween 350◦C and
450◦C. As epo ed in he li e a u e[30], hese s ages co espond o he
b eakdown o he ha d and so segmen s o he polyu e hane (PU)
chains, espec i ely. Table p esen ed in he Fig. 6(b) summa izes he
ini ial decomposi ion (T
i
) and he weigh pe cen ages o he esidue
emaining a he end o deg ada ion (% esidual weigh ).
The ini ial deg ada ion empe a u e (Ti) inc eases as he mic opa -
icle con en ises and he polyme con en dec eases, indica ing ha he
pa icles do no accele a e he ma e ial’s deg ada ion. In any case, hey
imp o e i s s abili y. The empe a u e a which he maximum weigh
loss a e (T
d
) occu s emains app oxima ely 390◦C ac oss all samples,
ega dless o mic opa icle concen a ion. Con e sely, he inal esidual
mass inc eases wi h a highe pe cen age o Fe
70
Co
30
magne ic pa icles,
as hey do no deg ade e en a empe a u es as high as 800◦C[31].
The magne ic p ope ies o he composi es we e e alua ed by
measu ing he magne ic hys e esis loops and magne os ic ion cu es.
The magne ic ield was applied wi h he o ien a ion (1, 0, 0). The
magne ic hys e esis loops o samples wi h di e en pa icles pe cen age,
wi h o ien a ion O 1 (0, 0, 1), as well as o pu e Fe
70
Co
30
, a e ep e-
sen ed in Fig. 7(a).
As expec ed, he sa u a ion magne iza ion o he MF inc ease as he
pe cen age o he Fe
70
Co
30
con en does, eaching a maximum alue
144 emu/g o he MF o 65 % w o mic opa icle, being he coe ci i y
negligible. I can be no ed ha o he 50 % w and 65 % w samples,
b anches o he espec i e hys e esis loops do no o e lap. Since his
beha iou only appea s a hese high mic opa icles con en pe cen -
ages, i may be a ibu ed o mo emen o he sample caused by he
applied magne ic ield a he han o a s uc u al p ope y. This
displacemen is much mo e p onounced a highe pe cen ages, as he
sample ends o espond mo e s ongly o he applied ield. This mo e-
men al e s he sample’s o ien a ion in a ou o he ield di ec ion,
esul ing in a cu e ha eaches sa u a ion ea lie han expec ed.
Consequen ly, he e ec o he o ien a ion o he MF wi h espec o he
applied magne ic ield was s udied o he MF o 40 %w con en o
mic opa icle. Those esul s a e ep esen ed in Fig. 7(c).
F om his Fig. 7(c), i is clea ha he way he sa u a ion magne i-
za ion is eached is consis en ac oss all samples. As expec ed, he
Fig. 7. Scheme o he o ien a ion o he magne ic ield du ing hys e esis loop measu emen s in ela ion o he alignmen o he magne ic mic opa icles (a). Hys-
e esis loops o MF
O 1
o 10, 30, 40, 50 and 65 % con en o Fe
70
Co
30
as well as he aw mic opa icles (b), and o MF wi h 40 % con en o Fe
70
Co
30
wi h di e en
alignmen s o he magne ic mic opa icles (c).
Fig. 8. Scheme o he o ien a ion o he magne ic ield du ing hys e esis loop measu emen s in ela ion o he alignmen o he magne ic mic opa icles and he
piezoelec ic s ain gauge (a). Magne os ic ion cu es o MF O 1 o ien a ion o 10, 30, 40, 50 and 65 %w con en o Fe
70
Co
30
(b), and o MF 40 %w con en wi h
di e en o ien a ions (c).
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
5
samples aligned wi h he applied magne ic ield (O 3) equi e he
lowes alue o applied magne ic ield o each sa u a ion, abou 0.7 T.
Among he o he o ien a ions, he MF wi h andomly o ien ed pa icles
(O 0) sa u a es a he applied magne ic ield o 1.0 T, while he ones
wi h o ien a ions O 1 and O 2 sa u a e abou a magne ic ield o 1.4 T.
These measu emen s e idence ha hese composi es a e highly aniso-
opic magne ic ma e ials, since hei hys e esis loops depend s ongly
on he di ec ion o he applied ield. Chains o magne ic pa icles exhibi
a single magne ic easy axis aligned wi h he chain di ec ion, esul ing
om s ong dipola in e ac ions be ween Fe₇₀Co₃₀ mic opa icles wi hin
he chain. Al hough he indi idual pa icles a e magne ically iso opic,
he collec i e dipola coupling induces aniso opy a he chain le el,
which domina es he magne ic esponse.
Fig 8(b) and (c) show he measu ed magne os ic ion cu es o he
MF unde wo di e en condi ions: (b) a ying Fe₇₀Co₃₀ con en , wi h
magne ic mic opa icles aligned pe pendicula ly o bo h he applied
magne ic ield and he magne os ic ion measu emen di ec ion (O 1);
and (c) a ixed Fe₇₀Co₃₀ concen a ion o 40 %, while he o ien a ion o
he applied magne ic ield a ies. The sample is ixed along one o i s
edges, as shown in Fig. 8(a).
The analysis o magne os ic ion cu es o MF oam wi h O 1 e-
eals a clea ela ionship be ween he Fe
70
Co
30
pa icle con en and he
magne os ic i e esponse. A low pa icle concen a ion o 10 %w ,
magne os ic ion alues a e low and posi i e. As he concen a ion in-
c eases, he absolu e magne os ic ion alue also inc eases bu becomes
nega i e, indica ing ma e ial comp ession. Fo he MF
30 %
O 1 sample,
he alue eaches –55 ppm and a peak nea –500 ppm is obse ed o he
MF
40 %
O 1. Howe e , when he mic opa icle concen a ion ises
u he ( o 50 and 65 %w ), he absolu e magne os ic ion alue de-
c eases bu emains nega i e (a ound –200 ppm). Building on hese
obse a ions, he in luence o magne ic pa icle o ien a ion on he
composi e’s magne os ic i e esponse was u he in es iga ed o he
MF
40 %
sample (Fig. 8(c)). The MF wi h andomly o ien ed pa icles
(O 0) does no exhibi any signi ican de o ma ion. In con as , he MF
wi h o ien a ion O 2 and O 3 exhibi s a posi i e magne os ic ion. In he
case o O 2, i eaches a alue o 30 ppm. Finally, MF wi h O 1 o ien-
a ion, as p e iously discussed, shows he highes nega i e de o ma ion
le els, nea ly –500 ppm.
This obse ed beha iou can be explained as a compe ing e ec
be ween he alignmen o he pa icles wi h he magne ic ield h ough
polyme ic oam s e ching, and hei alignmen due o ma e ial bending.
The comp ession unde gone by he MF ( e lec ed in a nega i e magne-
os ic ion) can be associa ed wi h a bending mechanism o he sample,
while he s e ching is expec ed o esul om he o que exe ed on he
chains o magne ic pa icles embedded wi hin he polyme oam, as hey
a emp o align wi h he applied magne ic ield. These compe ing
mechanisms ha e o be di ec ly co ela ed wi h he ma e ial’s me-
chanical beha iou . Thus, seeking o a be e unde s anding o he
obse ed phenomenon, he samples we e deeply analysed wi h espec
o hei mechanical p ope ies h ough bo h comp ession and DMA
measu emen s.
The esul s o he comp ession es s pe o med on a ious oam
samples a e p esen ed in Fig. 9. These es s we e conduc ed on samples
wi h he same mic opa icle concen a ion (40 w %) bu di e en o i-
en a ions (see Fig. 9(a)). Foam like s uc u es comp ession es s a e
ypically cha ac e ized by h ee dis inc egions [34]. The i s egion
exhibi s linea elas ic de o ma ion. Du ing he second egion, he po ous
s uc u e collapses due o plas ic bending. Finally, he hi d egion in-
ol es plas ic de o ma ion, whe e he po e walls s a in e ac ing as
po osi y is minimized.
Fig. 9 shows a s ong dependence o he mechanical beha iou
exhibi ed by he composi es on pa icle o ien a ion. Samples wi hou
pa icles and andomly o ien ed pa icles (RP case) show he ypical
beha iou o oam s uc u es desc ibed be o e. Ne e heless, he addi-
ion o he Fe
70
Co
30
mic opa icles inc eases he s i ness o he ma e ial
in he ini ial elas ic egion (Fig. 9(c)) and enhances he pla eau s ess in
Fig. 9. Scheme o he o ce di ec ion and mic opa icle chain o ien a ion du ing comp ession es s o MF wi h 40 %w magne ic pa icles (a). Rep esen a i e
s ess–s ain cu es om he comp ession es s (b). Young’s modulus in he elas ic egion (c), and pla eau s ess in he plas ic egion (d).
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
6
he plas ic egion (Fig. 9(d)), indica ing an o e all ein o cemen e ec .
Fo samples wi h pa icles aligned in he di ec ion o he applied o ce
(OP
II
case), he h ee dis inc egions a e e en mo e p onounced.
Ini ially, he samples a e s i e due o he alignmen o pa icle chains
wi h he applied o ce. As he s uc u e collapses, i ansi ions in o e-
gion 2, whe e plas ic de o ma ion occu s, esul ing in a pla eau wi h a
highe s ess han he samples wi hou pa icles and wi h andomly
o ien ed pa icles. Finally, as he oam cells begin o collapse and
in e ac , he s ess inc eases again, en e ing egion 3. In con as , o
samples wi h pa icles o ien ed pe pendicula ly o he o ce di ec ion
(OP
⊥
case), he ma e ial appea s o immedia ely en e egion 2, as he e
is li le o null esis ance a he beginning. While egion 1 is likely p e-
sen , i s con ibu ion is minimal and may be neglec ed, as he s ess
alues a e much lowe compa ed o he o he cases o o he alues
obse ed in egion 3 o he pa allel o ien a ion.
To he ligh o he p e iously ob ained da a and plausible explana-
ion, he impo ance o pa icle o ien a ion in he mechanical p ope ies
o oam composi es, and consequen ly in hei magne os ic i e
esponse o magne ic ields, becomes e iden .
Pa icles wi h he same o ien a ion as he magne ic ield (O 3)
exhibi li le o no de o ma ion. Since he pa icle chains a e al eady
aligned wi h he ield, hey do no exe any o que on he polyme
ma ix o eo ien hemsel es. Fo pa icles o ien ed along he O 2 di-
ec ion, he a emp o align wi h he magne ic ield induces s e ching
wi hin he ilm, which esul s in posi i e magne os ic ion. Con e sely,
o pa icles aligned along he O 1 di ec ion, alignmen wi h he applied
magne ic ield is mo e easily achie ed h ough bending a he han
s e ching. This is due o he o ien a ion o he pa icles, which me-
chanically a o bending as he dominan ealignmen mechanism.
When he wo-laye ed specimen bends, comp essi e s ess ac s on he
magne os ic i e ma e ial, causing i o sh ink. Is is ansla ed in o a
nega i e magne os ic ion alue. This beha io is obse ed because, a
Fig. 10. Illus a ion o he bending e ec (nega i e magne os ic ion) and s e ching p ocess (posi i e magne os ic ion) showed by MF unde he applica ion o a
magne ic ield in he samples wi h magne ic mic opa icles’s line in he di ec ion O 1 (a), O 2 (b) and O 3 (c).
Fig. 11. DMA esul s ob ained in single can ile e bending mode o MF wi h
magne ic mic opa icles aligned along O 1 and a ying pa icle concen a ions.
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
7
he s udied concen a ions, he mechanical p ope ies o he polyme
ma ix s ill suppo such de o ma ion modes, as will be u he discussed
in he ollowing sec ions. A schema ic ep esen a ion o his beha io is
shown in Fig. 10.
Nex essen ial s ep u ns ou o be he s udy o he e ec o pa icle
concen a ion in de ail. This analysis was ca ied ou wi h DMA
echnique and using a single can ile e clamp, aiming o unde s and
how he in oduc ion o pa icles a ec s he ma e ial’s bending
capabili y.
DMA measu emen s (see Fig. 11) indica e ha he addi ion o mag-
ne ic mic opa icles enhances he s i ness o he magne ic oam. When
he pa icle concen a ion anges be ween 10 % and 40 %w , he
Fig. 12. Image o he ob ained MFFs o he di e en Fe
70
Co
30
concen a ions.
Fig. 13. SEM images ob ained o he MFF wi h di e en mic opa icle con en : 0, 30, 50 and 65 %, ep esen ed in (a), (b), (c) and (d), espec i ely. (e) and ( ) a e
magni ied iews o speci ic a eas om images (c) and (d), espec i ely.
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
8
ma e ial emains su icien ly lexible o a ou he alignmen o pa icles
wi h he magne ic ield h ough bending a he han di ec s e ching.
This bending beha iou con ibu es o he obse ed nega i e magne o-
s ic ion. Howe e , as he concen a ion inc eases o 50 %w and espe-
cially o 65 %w , he ma e ial becomes signi ican ly s i e , educing i s
abili y o bend. Consequen ly, he absolu e alues o magne os ic ion
dec ease a hese highe concen a ions, al hough he magne os ic ion
emains nega i e.
3.2. Magne ic oam ilms (MFF)
Finally, a new se o magne ic composi es was p epa ed using wi h
he oam ilm s uc u e (MFF): ollowing he p ocedu e p e iously
desc ibed in Sec ion 2, MFFs we e p epa ed wi h a ied Fe
70
Co
30
con-
en (10, 30, 40, 50 and 65 %w ). Fig. 12 shows he ob ained MFFs o
he di e en mic opa icle con en .
SEM images showed in Fig. 13 e eal he high pe cen age o po ous
su ace in all hese ma e ials, con i ming he expec ed ou come. Addi-
ionally, i is obse ed ha wi h inc easing concen a ions o o ien ed
mic opa icles, up o 50 %w , he pa icles align in chains along he
di ec ion o he applied ield (Fig. 12(b) and (c)). Howe e , a highe
concen a ions, he mic opa icles begin o agglome a e, o ming
hicke dend i e-like s uc u es and esul ing in a less homogeneous
ma e ial (Fig. 12(d)). These esul s ag ee wi h he obse a ions made
wi h MF, whe e simila Composi es wi h highe amoun o Fe
70
C0
30
pa icles exhibi ed phase seg ega ion be ween he polyme and mag-
ne ic ille componen o he hyb id ma e ial.
Magne os ic ion measu emen s we e ca ied ou in MFF wi h mag-
ne ic mic opa icles in O 3 o ien a ion, as he magne os ic ion esul s
o MF was maximum a ha pa icula o ien a ion. The esul s o he
di e en concen a ions o Fe
70
Co
30
magne ic ille a e shown in Fig. 14.
As i happened o he MF, he magne os ic ion cu es o MFF a e
highly dependen on Fe
70
Co
30
mic opa icle con en . A low concen-
a ions abou a 10 %w , magne os ic ion alues a e low (∼12 ppm)
and posi i e. As he mic opa icle concen a ion inc eases, magne o-
s ic ion becomes nega i e, bu wi h highe absolu e alues, indica ing
ma e ial comp ession. Fo ille concen a ions be ween 30 % and 40 %
w , he magne os ic ion eaches alues abou –20 and –118 ppm,
espec i ely.
Howe e , o concen a ions abo e 50 %w , he magne os ic i e
alues become posi i e, sugges ing he concu ence o a s e ching
p ocess. Fo he concen a ion o 65 %w o mic opa icles, he
magne os ic ion eaches a alue o +80 ppm. Once again, i appea s o
be a compe i ion be ween wo mechanisms: he alignmen o he mag-
ne ic pa icles wi h he magne ic ield h ough polyme ic oam
s e ching which leads o posi i e magne os ic ion alues, s. hei
alignmen ia ma e ial bending, which causes local ilm comp ession
and esul s in nega i e magne os ic ion. The mechanical beha iou will
ul ima ely de e mine which e ec is uling, o each composi e.
DMA measu emen s using a dual can ile e clamp (see Fig. 15)
e eal ha he inco po a ion o magne ic mic opa icles inc eases he
igidi y o he oam ilm. Fo pa icle concen a ions be ween 10 % and
40 %w , he ma e ial emains lexible enough o a ou bending e ec
o e di ec s e ching, leading as a whole o he obse a ion o a nega-
i e magne os ic ion alue. Howe e , as he concen a ion eaches 50
and pa icula ly a 65 %w , s i ness inc eases signi ican ly. A hese
highes concen a ions, bending is la gely supp essed, and he alignmen
o magne ic pa icles wi h he applied ield p ima ily occu s h ough he
s e ching o he polyme ic oam. This is due o he magne ic o que
su e ed by he pa icles[32] as hey a emp o align wi h he ield,
inducing s ess in he polyme ma ix and esul ing in a o al, global
posi i e magne os ic ion alue. This ansi ion om bending-d i en o
s e ching-d i en beha iou is a di ec consequence o he inc easing
s i ness, as con i med by DMA es s. A g aphic scheme o hese wo
di e en e ec s is p esen ed in Fig. 16.
4. Conclusions
In his s udy, we analyzed he magne ic esponse o so magne ic
polyu e hane oams loaded wi h di e en amoun s and o ien a ions o
Fe₇₀Co₃₀ magne ic mic opa icles. The obse ed inal s uc u e o he
p epa ed ma e ial is clea ly dependen on whe he he oam was
allowed o expand eely (MF) o was con ined wi hin a es ic ed ol-
ume (MFF). Composi es we e p epa ed and cha ac e ized in e ms o
hei mo phological, he mal, mechanical, and magne ic p ope ies.
I has been ound ha he in oduc ion o magne ic mic opa icles
does no signi ican ly a ec he he mal p ope ies o he ma e ial, wi h
no signi ican changes eco ded in he he mal deg ada ion p ocesses.
On he o he hand, bo h magne ic and mechanical p ope ies a e
g ea ly a ec ed by he amoun and o ien a ion o he mic opa icles,
being ha magne ic pa icles chains p esen a single magne ic easy axis
o ien ed along he chain axis.
The magne os ic ion es s a e highly dependen on bo h he o ien-
a ion and concen a ion o mic opa icles. The e is a compe ing e ec
be ween he bending and s e ching o he ma e ial as pa icle chains
a emp o align wi h he magne ic ield. Bending leads o ma e ial
comp ession, esul ing in nega i e magne os ic ion alues, while
Fig. 14. Magne os ic ion cu es o MFF wi h Fe₇₀Co₃₀ mic opa icles o ien ed
along he O 1 di ec ion, o 10, 30, 40, 50, and 65 w % concen a ions.
Fig. 15. DMA esul s ob ained in dual can ile e bending mode o MFF wi h
magne ic mic opa icles aligned along O 1 and a ying pa icle concen a ions.
A. Lashe as e al.
Senso s and Ac ua o s: A. Physical 394 (2025) 116949
9
