Ci a ion: Salaheldeen, M.; Wede ni,
A.; Ipa o , M.; Zhuko a, V.; Lopez
An on, R.; Zhuko , A. Enhancing he
Squa eness and Bi-Phase Magne ic
Swi ching o Co2FeSi Mic owi es o
Sensing Applica ion. Senso s 2023,23,
5109. h ps://doi.o g/10.3390/
s23115109
Academic Edi o : Ch is e
Johansson
Recei ed: 11 Ap il 2023
Re ised: 13 May 2023
Accep ed: 25 May 2023
Published: 26 May 2023
Copy igh : © 2023 by he au ho s.
Licensee MDPI, Basel, Swi ze land.
This a icle is an open access a icle
dis ibu ed unde he e ms and
condi ions o he C ea i e Commons
A ibu ion (CC BY) license (h ps://
c ea i ecommons.o g/licenses/by/
4.0/).
senso s
A icle
Enhancing he Squa eness and Bi-Phase Magne ic Swi ching o
Co2FeSi Mic owi es o Sensing Applica ion
Mohamed Salaheldeen 1,2,3,4,* , Asma Wede ni 1,2,4 , Mihail Ipa o 1,2, Valen ina Zhuko a 1,2,4 ,
Rica do Lopez An on 5,* and A cady Zhuko 1,2,4,6
1Depa men o Polyme s and Ad anced Ma e ials, Facul y o Chemis y, Uni e si y o he Basque Coun y,
UPV/EHU, 20018 San Sebas ián, Spain
2Depa men o Applied Physics I, EIG, Uni e si y o he Basque Coun y, UPV/EHU,
20018 San Sebas ián, Spain
3Physics Depa men , Facul y o Science, Sohag Uni e si y, Sohag 82524, Egyp
4EHU Quan um Cen e , Uni e si y o he Basque Coun y, UPV/EHU, 20018 San Sebas ián, Spain
5Depa men o Applied Physics, Regional Ins i u e o Applied Scien i ic Resea ch (IRICA),
Uni e si y o Cas illa-La Mancha, 13071 Ciudad Real, Spain
6IKERBASQUE, Basque Founda ion o Science, 48011 Bilbao, Spain
*Co espondence: [email p o ec ed] (M.S.); [email p o ec ed] (R.L.A.)
Abs ac :
In he cu en s udy we ha e ob ained Co
2
FeSi glass-coa ed mic owi es wi h di e en
geome ical aspec a ios,
ρ
= d/D
o
(diame e o me allic nucleus, d and o al diame e , D
o
). The
s uc u e and magne ic p ope ies a e in es iga ed a a wide ange o empe a u es. XRD analysis
illus a es a no able change in he mic os uc u e by inc easing he aspec a io o Co
2
FeSi-glass-
coa ed mic owi es. The amo phous s uc u e is de ec ed o he sample wi h he lowes aspec
a io (
ρ
= 0.23), whe eas a g ow h o c ys alline s uc u e is obse ed in he o he samples (aspec
a io
ρ
= 0.30 and 0.43). This change in he mic os uc u e p ope ies co ela es wi h d ama ic
changing in magne ic p ope ies. Fo he sample wi h he lowes
ρ
- a io, non-pe ec squa e loops a e
ob ained wi h low no malized emanen magne iza ion. A no able enhancemen in he squa eness
and coe ci i y a e ob ained by inc easing
ρ
- a io. Changing he in e nal s esses s ongly a ec s he
mic os uc u e, esul ing in a complex magne ic e e sal p ocess. The he momagne ic cu es show
la ge i e e sibili y o he Co
2
FeSi wi h low
ρ
- a io. Meanwhile, i we inc ease he
ρ
- a io, he sample
shows pe ec e omagne ic beha io wi hou i e e sibili y. The cu en esul illus a es he abili y
o con ol he mic os uc u e and magne ic p ope ies o Co
2
FeSi glass-coa ed mic owi es by changing
only hei geome ic p ope ies wi hou pe o ming any addi ional hea ea men . The modi ica ion
o geome ic pa ame e s o Co
2
FeSi glass-coa ed mic owi es allows o ob ain mic owi es ha exhibi
an unusual magne iza ion beha io ha o e s oppo uni ies o unde s and he phenomena o a ious
ypes o magne ic domain s uc u es, which is essen ially help ul o designing sensing de ices based
on he mal magne iza ion swi ching.
Keywo ds:
Heusle alloys; glass-coa ed mic owi es; mul i-s ep magne ic beha io ; sensing applica ions
1. In oduc ion
The use o e omagne ic ma e ials in spin onic applica ions has ga ne ed inc easing
a en ion in ecen yea s due o hei unique magne ic p ope ies ha enable he con ol
and manipula ion o spin cu en s. Among he di e en ypes o e omagne ic ma e ials,
mic o/nano-s uc u ed ma e ials ha e eme ged as p omising candida es o enhancing
spin onic de ices’ pe o mance [
1
–
9
]. One o he mos p omising mul idisciplina y e-
sea ch ields is spin onics, which enables he c ea ion o he nex gene a ion o nano &
mic ode ices wi h imp o ed p ocessing and memo y capabili y while consuming less
powe [
10
]. To add ess he a ious equi ed c i e ia, such as high spin pola iza ion o high
Senso s 2023,23, 5109. h ps://doi.o g/10.3390/s23115109 h ps://www.mdpi.com/jou nal/senso s
Senso s 2023,23, 5109 2 o 14
Cu ie empe a u e, Tc, a new gene a ion o ma e ials wi h mul i unc ion uses has o be c e-
a ed [
11
]. These Heusle compounds a e well sui ed o spin onic and magne o-elec onic
applica ions [
12
]. Be ween he ad an ages o hese compounds, we can highligh se e al
ones: good la ice ma ching wi h he mos ypical subs a es, Tc abo e oom empe a u e,
and he possibili y o ob aining close o 100% o spin pola ized nea he Fe mi le el [
11
–
15
].
In pa icula , Co
2
-based ull-Heusle compounds a e among he mos p omis-
ing hal -me allic alloys due o hei high he mal s abili y, high Cu ie empe a u es
(
Tc ≈1100 K
) in bulk o m, high magne ic momen (~6
µB
/ .u.), and low Gilbe damp-
ing cons an (
α
= 0.004) [
14
,
16
,
17
]. Addi ionally, hey exhibi in e es ing anspo p op-
e ies and high magne ic momen s. I is no ewo hy ha hese Co
2
-based Heusle alloys
p esen a signi ican anomalous Hall linked o he eno mous Be y cu a u e associa ed
wi h hei band s uc u e [
16
,
18
]. All he p eceden e idence why he scien i ic commu-
ni y is so in e es ed nowadays in Co-based ull-Heusle alloys. Hence, hese alloys a e
ex ensi ely esea ched in se e al con igu a ions: nanopa icles [
19
], hin ilms [
15
,
17
,
20
],
and nano/mic owi es [
21
–
24
]. I is ele an o no e ha he ab ica ion o Heusle alloys
nanopa icles and hin ilms aces se e al di icul ies o applica ion pu poses, including
he high cos o p epa a ion me hods, chemical composi ion inhomogenei y, and ease
o oxida ion [
20
]. The di usion o subs a e a oms in o he ilm esul s in he exis ence
o he a omic diso de and phase sepa a ions, which a e commonly obse ed [
25
], in
addi ion o he la ice misma ch be ween he alloy and he subs a e. Fu he mo e,
in o de o s a he equisi e s uc u al o de ing, he a c-mel ed o hin- ilm- o med
Heusle alloys need leng hy, high- empe a u e annealing p ocedu es [26].
Magne ic wi e esea ch has ecei ed a lo o in e es du ing he las se e al decades [
27
].
The ocus is on amo phous magne ic wi es, which can exhibi unusual magne ic ea-
u es such as spon aneous magne ic bis abili y o he Gian magne oimpedance phe-
nomenon [
27
,
28
]. Se e al manu ac u ing p ocesses in ol ing as solidi ica ion can be
used o c ea e magne ic wi es con aining amo phous and/o nanoc ys alline phases [
27
,
28
].
Ne e heless, only he Taylo -Uli o sky manu ac u ing app oach allows he p epa a ion o
magne ic mic owi es wi h he wides diame e ange ( om 0.2 o 100
µ
m) [
27
,
28
]. Such
mic owi es a e composi es consis ing o me allic nuclei (wi h 0.2
≤
d
≤
100
µ
m) usually
comp ised o i on, cobal , nickel, o hei alloys, co e ed by hin, lexible, and insula ing
glass ( ypically Py ex o Du an) coa ing ( ypically wi h hickness om 0.5 o 10
µ
m) [
27
,
28
].
As a esul , he p ospec i e applica ions o glass-coa ed mic owi es in sensing, ac ua ion,
and biomedical enginee ing ha e been expanded. The insula ing and lexible glass coa -
ing p o ec s he mic owi es om oxida ion, co osion, and o he en i onmen al ac o s
while simul aneously gi ing hem ou s anding mechanical s abili y. Mo eo e , he glass
laye and he magne ically lexible amo phous me allic nucleus p o ide high sensi i i y
o ex e nal s imuli including magne ic ields, empe a u e luc ua ions, and mechanical
s ess [
27
–
35
]. Such sensi i i y is connec ed o he e omagne ic o igin o he me allic
nucleus, which esponds o he applied s imulus. Inno a i e senso s ha moni o magne ic
ields, empe a u e, and s ess ha e been de eloped using glass-coa ed mic owi es o
a ange o applica ions [
27
–
29
]. Addi ionally, hey ha e shown po en ial cha ac e is ics
o ac ua o s and in medical applica ions, including cance ea men ( h ough magne ic
hype he mia) [
29
] and medicine adminis a ion. Fu u e echnological ad ancemen s can
use glass-coa ed mic owi es because o hei dis inc i e combina ion o p ope ies [27,29].
In his a icle, we epo an a emp o p epa e Co2FeSi glass-coa ed mic owi es wi h
a iable geome ical aspec a ios
ρ
= d/D
o
(being d-diame e o he me allic nucleus
and D
o
— o al diame e ). The ab ica ion me hod was chosen because o he in e es -
ing ela ionship be ween he magne ic and s uc u al p ope ies in he case o Heusle
alloys in he o m o glass-coa ed mic owi es, coupled wi h he p ope ies p o ided by
his ab ica ion me hod: excellen mechanical p ope ies, insula ing beha io , hin and
lexible glass-coa ing, and small dimensionali y [
27
,
29
–
35
]. As a esul , we ha e p epa ed
Co
2
FeSi glass-coa ed mic owi es using he Taylo -Uli o sky p ocedu e, which is de ailed
p e iously [
27
,
36
,
37
]. The Taylo -Uli o sky me hod, which has been ai ly u ilized since
Senso s 2023,23, 5109 3 o 14
he 1960s [
37
], is p obably he mos used ab ica ion me hod o make Heusle alloys glass-
coa ed mic owi es wi h a wide a ie y o geome ic cha ac e is ics [
21
,
22
,
24
,
27
–
35
]. The
p ima y bene i o his non-expensi e echnique is ha i allows he p oduc ion o hin
and long (up o se e al kilome e s long) mic owi es wi h a wide diame e ange ( om
0.2
µ
m up o 100
µ
m) a a high a e (up o some hund ed me e s pe minu e) [
36
–
38
].
This p ocess is also used o p epa e glass-coa ed mic owi es wi h excellen mechanical
p ope ies [
21
,
39
–
41
]. Addi ional bene i s o glass coa ing on mic owi es a e be e isola-
ion and p o ec ion om he su oundings. Mo eo e , he ac ha he glass coa ing is
biocompa ible, coupled wi h he commen ed p ope ies, make his app oach well-sui ed
o biological applica ions [
29
,
42
,
43
]. The e o e, Heusle mic owi es o Co
2
FeSi a e an
in e es ing ma e ial o a b oad ange o applica ions and de ices. As a as we know, he e
is no epo up o da e on he p oduc ion and s uc u al, mechanical, o magne ic p ope ies
o Co
2
FeSi-based glass-co e ed Heusle mic owi es wi h a ied
ρ
- a ios, as well as he
in es iga ion o i s in luence on magne o-s uc u e beha io .
2. Ma e ials and Me hods
A c mel ing is a me hod o manu ac u ing Co
2
FeSi alloys ha in ol es mel ing he p e-
cu so componen s oge he in an elec ic a c u nace. Typically, he ollowing p ocedu es
a e used o c ea e Co
2
FeSi alloys by a c mel ing: (i) p epa ing he p ecu so ing edien s. The
p ecu so elemen s o he Co
2
FeSi alloy a e weighed and deposi ed in a g aphi e c ucible,
con aining cobal (powde ) (99.99%), i on (powde ) (99.9%), and silicon (powde ) (99.99%)
supplied by Technoamo S.R.L. Co. (Cisineu, Molda ia). (ii) The ma e ials mel ing. The
c ucible con aining he p ecu so ma e ials is pu in an elec ic a c u nace, and an elec ical
cu en is ed h ough he ma e ials o s a he mel ing p ocess in a acuum and a gon a mo-
sphe e. The u nace empe a u e is p ecisely egula ed o ensu e ha he ing edien s mel
and mix equally. (iii) The cooling and solidi ica ion p ocesses. The c ucible is wi hd awn
om he u nace and allowed o cool once he componen s ha e mel ed and combined.
The Co
2
FeSi alloy (ingo ) is c ea ed as he ing edien s consolida e. This p ocess was hen
epea ed i e imes o achie e pe ec homogenei y and a homogeneous mic os uc u e.
Once he Co
2
FeSi alloy has solidi ied and o med an ingo , he ingo is used o p epa e
Co
2
FeSi glass-coa ed mic owi es using he Taylo -Uli o sky p ocess. As desc ibed in he
in oduc ion, he Taylo -Uli o sky p epa a ion echnique o e s signi ican bene i s o e
al e na i e p ocedu es o manu ac u ing glass-coa ed mic owi es. One ad an age is ha i
enables he ab ica ion o mic owi es wi h a he hin glass coa ings, gene ally up o a ew
mic ome e s hick. This hin insula ing coa ing pe mi s he elec ical and magne ic cha ac-
e is ics o he mic owi e me allic nucleus o be p ese ed, making he esul an mic owi es
aluable o a wide ange o applica ions. Many p io publica ions [
21
,
22
,
24
,
27
–
35
] explain
he manu ac u ing me hod in de ail. To summa ize i , a glass capilla y was illed wi h
Co
2
FeSi alloy, mol en using a high equency induc o o hea ing an ingo o e i s mel ing
empe a u e. The a ia ion o he speed o wi e d awing, alloy empe a u e, glass ube
eed a e and o he o a ion o he pick-up bobbin we e he pa ame e s used o con ol he
diame e o he me allic nuclei, dme al (µm), and o al diame e D o al (µm) as explained in
de ail elsewhe e [
38
]. Finally, he mic owi e is cooled wi h a coolan s eam o comple e he
apid mel quenching p ocess. All geome ic pa ame e s o samples in es iga ed in cu en
s udy a e lis ed in Table 1, also including a simila sample p e iously s udied (in e . [
24
]),
whose esul s will be also discussed in he ollowing sec ion.
Senso s 2023,23, 5109 4 o 14
Table 1.
The geome ical pa ame e s d
me al
(
µ
m), D
o al
(
µ
m), aspec a io, and a e age (A .) o a omic
pe cen age o Co, Fe, and Si elemen al composi ion in Co2FeSi glass-coa ed mic owi es.
Sample dme al (µm) D o al (µm) Aspec Ra io (ρ) Chemical Composi ion
GCMWA5.1 ±0.1 22.2 ±0.1 0.23 ±0.01 Co44Fe23Si33
GCMW** 4.4 ±0.1 17.6 ±0.1 0.25 ±0.01 Co44Fe23Si33
GCMWB6.4 ±0.1 21.3 ±0.1 0.30 ±0.01 Co44Fe23Si33
GCMWC7.7 ±0.1 17.9 ±0.1 0.43 ±0.01 Co44Fe23Si33
GCMW**: Co2FeSi glass-coa ed mic owi es wi h (ρ= 0.25) [24].
We used Scanning Elec on Mic oscopy (SEM) and Ene gy Dispe si e X- ay (EDX)
(JEOL-6610LV, JEOL L d., Tokyo, Japan) o de e mine he aspec
ρ
- a io o Co
2
FeSi glass-
coa ed mic owi es samples and i s ela ed nominal chemical composi ion.
The XRD s uc u e analysis was ca ied on by using X- ay di ac ion (XRD) BRUKER
(D8 Ad ance, B uke AXS GmbH, Ka ls uhe, Ge many).
The magne ic beha io was s udied in wo di e en ways: hys e esis loops a empe a-
u es be ween 5 and 350 K, and he momagne ic cu es ollowing h ee di e en p o ocols,
ze o ield cooling (ZFC), ield cooling (FC), and ield hea ing (FH) a he low magne ic
ield (H = 200 Oe). All magne iza ion cu es we e measu ed using a PPMS (Physical
P ope y Magne ic Sys em, Quan um Design Inc., San Diego, CA, USA) ib a ing-sample
magne ome e a empe a u es, T, be ween 5 and 400 K o ZFC, FC, and FH magne ic
cu es. Fo he hys e esis loops, we only ocus on he in-plane con igu a ion whe e he
applied magne ic ield is pa allel o he wi e axis. The esul s a e p o ided in e ms o he
no malized magne iza ion, M/M
5K
, whe e M
5K
is he magne ic momen ob ained a 5 K
o a oid misleading o he es ima ion o he e o s in he es ima ion o he magne iza ion
sa u a ion alues.
3. Resul s
3.1. Analysis o Chemical and S uc u al Da a
The geome ies (
ρ
- a ios) and chemical composi ions o p epa ed samples a e shown
in Table 1. The a ia ion o he mic owi es diame e s (d
me al
and D
o al
) is achie ed by
con olling he d awing a e, alloy empe a u e, glass ube eed a e, and he ecei ing
bobbin o a ion speed [
38
]. Using he EDX da a om Table 1, i was e ealed ha he
me allic nucleus composi ion di e ed conside ably om he s oichiome ic one (Co
2
FeSi).
The ea u es o he p epa a ion p ocess, which in ol ed alloy mel ing and d awing, we e
he cause o his sligh a ia ion. To quan i y he di e ence, we checked he nominal
composi ion o eigh si es as illus a ed in Figu e 1a. An a omic a e age o Co
44
Fe
23
Si
33
was used o con i m ha he ue 2:1 a io o Co and Fe was applied in all si es. A high Si
a io was ound because o he in e acial laye ha exis s be ween he me allic nucleus and
he glass co e ing.
Senso s 2023, 23, 5109 4 o 14
Table 1. The geome ical pa ame e s d
me al
(µm), D
o al
(µm), aspec a io, and a e age (A .) o a omic
pe cen age o Co, Fe, and Si elemen al composi ion in Co
2
FeSi glass-coa ed mic owi es.
Sample d
me al
(µm) D
o al
(µm) Aspec Ra io (ρ) Chemical Composi ion
GCMW
A
5.1 ± 0.1 22.2 ± 0.1 0.23 ± 0.01 Co
44
Fe
23
Si
33
GCMW** 4.4 ± 0.1 17.6 ± 0.1 0.25 ± 0.01 Co
44
Fe
23
Si
33
GCMW
B
6.4 ± 0.1 21.3 ± 0.1 0.30 ± 0.01 Co
44
Fe
23
Si
33
GCMW
C
7.7 ± 0.1 17.9 ± 0.1 0.43 ± 0.01 Co
44
Fe
23
Si
33
GCMW**: Co
2
FeSi glass-coa ed mic owi es wi h (ρ = 0.25) [24].
We used Scanning Elec on Mic oscopy (SEM) and Ene gy Dispe si e X- ay (EDX)
(JEOL-6610LV, JEOL L d., Tokyo, Japan) o de e mine he aspec ρ- a io o Co
2
FeSi glass-
coa ed mic owi es samples and i s ela ed nominal chemical composi ion.
The XRD s uc u e analysis was ca ied on by using X- ay diff ac ion (XRD) BRUKER
(D8 Ad ance, B uke AXS GmbH, Ka ls uhe, Ge many).
The magne ic beha io was s udied in wo diffe en ways: hys e esis loops a em-
pe a u es be ween 5 and 350 K, and he momagne ic cu es ollowing h ee diffe en p o-
ocols, ze o ield cooling (ZFC), ield cooling (FC), and ield hea ing (FH) a he low mag-
ne ic ield (H = 200 Oe). All magne iza ion cu es we e measu ed using a PPMS (Physical
P ope y Magne ic Sys em, Quan um Design Inc., San Diego, CA, USA) ib a ing-sample
magne ome e a empe a u es, T, be ween 5 and 400 K o ZFC, FC, and FH magne ic
cu es. Fo he hys e esis loops, we only ocus on he in-plane con igu a ion whe e he
applied magne ic ield is pa allel o he wi e axis. The esul s a e p o ided in e ms o he
no malized magne iza ion, M/M
5K
, whe e M
5K
is he magne ic momen ob ained a 5 K o
a oid misleading o he es ima ion o he e o s in he es ima ion o he magne iza ion
sa u a ion alues.
3. Resul s
3.1. Analysis o Chemical and S uc u al Da a
The geome ies (ρ- a ios) and chemical composi ions o p epa ed samples a e shown
in Table 1. The a ia ion o he mic owi es diame e s (d
me al
and D
o al
) is achie ed by con-
olling he d awing a e, alloy empe a u e, glass ube eed a e, and he ecei ing bobbin
o a ion speed [38]. Using he EDX da a om Table 1, i was e ealed ha he me allic
nucleus composi ion diffe ed conside ably om he s oichiome ic one (Co
2
FeSi). The ea-
u es o he p epa a ion p ocess, which in ol ed alloy mel ing and d awing, we e he
cause o his sligh a ia ion. To quan i y he diffe ence, we checked he nominal compo-
si ion o eigh si es as illus a ed in Figu e 1a. An a omic a e age o Co
44
Fe
23
Si
33
was used
o con i m ha he ue 2:1 a io o Co and Fe was applied in all si es. A high Si a io was
ound because o he in e acial laye ha exis s be ween he me allic nucleus and he glass
co e ing.
Figu e 1. The c oss sec ion o selec ed Co
2
FeSi glass-coa ed mic owi es wi h aspec a io 0.30 images
(a) and he chemical composi ion spec a o EDX o one o he poin s (b).
Figu e 1.
The c oss sec ion o selec ed Co
2
FeSi glass-coa ed mic owi es wi h aspec a io 0.30 images
(a) and he chemical composi ion spec a o EDX o one o he poin s (b).
Senso s 2023,23, 5109 5 o 14
In o de o s udy he o de s a e o ou p oduced Co
2
FeSi glass-coa ed mic owi es,
and o elucida e he e ec o he aspec a io modi ica ion on he c ys alline s uc u e, XRD
s uc u e analysis was ca ied on by using X- ay di ac ion (XRD).
As illus a ed in Figu e 2, he change in he geome ic
ρ
- a io has a s ong in luence
on he s uc u e o Co
2
FeSi glass-coa ed mic owi es. Fo he sample wi h he lowes
ρ
- a io, i.e.,
ρ
= 0.25, he sample shows an amo phous s uc u e whe e no c ys alline
peaks a e de ec ed. The wide halo a 2
θ
= 22.3
◦
is ela ed o he glass coa ing laye ,
as epo ed in ou p e ious wo ks [
21
,
22
,
24
,
27
–
35
]. By inc easing he geome ic aspec
a io, a c ys alline s uc u e o he me allic nucleus becomes e iden wi h a no able peak
a 2
θ
= 46.2
◦
, a ibu ing o he (220) e lec ion. Fu he inc ease o geome ic
ρ
- a io
esul s in he pe ec c ys alline s uc u e o samples s udied, whe e he c ys alline peak
in ensi y inc eases and an addi ional peak appea s a 2
θ
= 85.4
◦
, co esponding o he
(422) e lec ion. The analysis o XRD p o iles o he wo c ys alline Co
2
FeSi samples, i.e.,
GCMW
C
(
ρ
= 0.30) and GCMW
B
(
ρ
= 0.43), indica es an A2 single-phase s uc u e wi h a
small e agonal dis o ion ( aces o e agonal ma ensi e phase), and a b oadened peak
a ound 22
◦
a ibu ed o an amo phous s a e o GCMW
C
and mixed L2
1
o B2 phases wi h
he amo phous s a e o GCMWBsample [34,35].
Senso s 2023, 23, 5109 5 o 14
In o de o s udy he o de s a e o ou p oduced Co
2
FeSi glass-coa ed mic owi es,
and o elucida e he effec o he aspec a io modi ica ion on he c ys alline s uc u e, XRD
s uc u e analysis was ca ied on by using X- ay diff ac ion (XRD).
As illus a ed in Figu e 2, he change in he geome ic ρ- a io has a s ong in luence
on he s uc u e o Co
2
FeSi glass-coa ed mic owi es. Fo he sample wi h he lowes ρ-
a io, i.e., ρ = 0.25, he sample shows an amo phous s uc u e whe e no c ys alline peaks
a e de ec ed. The wide halo a 2Ө = 22.3° is ela ed o he glass coa ing laye , as epo ed
in ou p e ious wo ks [21,22,24,27–35]. By inc easing he geome ic aspec a io, a c ys al-
line s uc u e o he me allic nucleus becomes e iden wi h a no able peak a 2Ө = 46.2°,
a ibu ing o he (220) e lec ion. Fu he inc ease o geome ic ρ- a io esul s in he pe -
ec c ys alline s uc u e o samples s udied, whe e he c ys alline peak in ensi y inc eases
and an addi ional peak appea s a 2Ө = 85.4°, co esponding o he (422) e lec ion. The
analysis o XRD p o iles o he wo c ys alline Co
2
FeSi samples, i.e., GCMW
C
(ρ = 0.30)
and GCMW
B
(ρ = 0.43), indica es an A2 single-phase s uc u e wi h a small e agonal dis-
o ion ( aces o e agonal ma ensi e phase), and a b oadened peak a ound 22
⁰
a ibu ed
o an amo phous s a e o GCMW
C
and mixed L2
1
o B2 phases wi h he amo phous s a e
o GCMW
B
sample [34,35].
Figu e 2. XRD analysis o Co
2
FeSi glass-coa ed mic owi es wi h diffe en aspec a io measu ed a
oom empe a u e. The inse o Figu e 2 indica es he A2- ype cubic s uc u e.
The (220) and (422) e lec ions in GCMW
C
sample a e spli due o some e agonal
dis o ions o he c ys al la ice. A simila phenomenon was seen and discussed elsewhe e
[44]. I is known ha a spli in he b ag diff ac ion pa e ns leads o a small dis o ion o
he c ys alline s uc u e [45]. The absence o a (400) peak a ound 85°, which is expec ed o
be p esen in he A2 s uc u e, inc eases he possibili y ha he c ys alli es a e oo ine o
be de ec ed by X- ays, as epo ed elsewhe e [46]. In addi ion, he absence o some peaks
can be caused by a simila sca e ing ac o o he cons i uen elemen s (Co, Fe, and Si)
Figu e 2.
XRD analysis o Co
2
FeSi glass-coa ed mic owi es wi h di e en aspec a io measu ed a
oom empe a u e. The inse o Figu e 2indica es he A2- ype cubic s uc u e.
The (220) and (422) e lec ions in GCMW
C
sample a e spli due o some e agonal dis-
o ions o he c ys al la ice. A simila phenomenon was seen and discussed elsewhe e [
44
].
I is known ha a spli in he b ag di ac ion pa e ns leads o a small dis o ion o he
c ys alline s uc u e [
45
]. The absence o a (400) peak a ound 85
◦
, which is expec ed o
be p esen in he A2 s uc u e, inc eases he possibili y ha he c ys alli es a e oo ine
Senso s 2023,23, 5109 6 o 14
o be de ec ed by X- ays, as epo ed elsewhe e [
46
]. In addi ion, he absence o some
peaks can be caused by a simila sca e ing ac o o he cons i uen elemen s (Co, Fe, and
Si) [
47
]. O he wise, acco ding o he heo e ical ou comes o Zhang e al., he diso de ed
A2 s a e is mo e ene ge ically p e e able han hose o he o de ed L2
1
o B2 phases [
48
,
49
].
Ne e heless, he well-de ined and sha p di ac ion pa e ns in his sample (GCMW
C
sample) indica e a high c ys allini y, as compa ed wi h he o he wo XRD spec a. As he
de elopmen o aces o he seconda y phase ( e agonal ma ensi e) can a ec magne ic
beha io , his will be explo ed in mo e de ail in he ollowing sec ions.
We es ima ed he la ice pa ame e s o he wo c ys alline Co
2
FeSi glass-coa ed mi-
c owi es, and hen we employed he Debye-Sche e ’s equa ion, as p esen ed in ou p e-
ious wo k [
23
], o in es iga e he mic os uc u e o Co
2
FeSi in g ea e dep h. Using his
me hodology, we can es ima e he a e age g ain size, D
g
, associa ed wi h he p incipal
peaks, which is app oxima ely 17.8 m, 37.6 nm, and 45.8 nm o GCMW**, GCMW
B
, and
GCMW
C
o Co
2
FeSi mic owi es, espec i ely, as illus a ed in Table 2. Thus, D
g
has a
mono onic inc ease wi h inc easing he aspec a io.
Table 2.
The a e age g ain size and la ice pa ame e s o Co
2
FeSi glass-coa ed mic owi es wi h
di e en aspec a ios.
Sample A e age G ain Size (nm) La ice Pa ame e s (Å)
GCMWA- -
GCMW** 17.8 ±0.1 5.64 ±0.01
GCMWB37.6 ±0.1 5.63 ±0.01
GCMWC45.8 ±0.1 2.81 ±0.01
GCMW**: Co2FeSi glass-coa ed mic owi es wi h (ρ= 0.25) [24].
3.2. Magne ic Cha ac e iza ion
3.2.1. Room Tempe a u e Magne ic P ope ies
Figu e 3shows he magne ic hys e esis loops o Co
2
FeSi-glass-coa ed mic owi es wi h
di e en
ρ
- a ios, ob ained a oom empe a u e wi h an applied magne ic ield pa allel
o he mic owi e axis. All samples exhibi ypical e omagne ic beha iou , due o he
high Cu ie poin o Co
2
FeSi alloy g ea e han 1100 K [
46
]. The sample wi h a low
ρ
- a io
exhibi s so magne ic p ope ies wi h coe ci i y, H
c
, a ound 14 Oe, and a non-squa e
hys e esis loop shape (Figu e 3a). Howe e , he sample wi h he la ges
ρ
- a io shows
almos pe ec ly squa e hys e esis loops wi h highe H
c
(abou 87 Oe), han Co
2
FeSi wi h
a low
ρ
- a io (see Figu e 3b,c). In addi ion, he hys e esis loop shows mul is ep magne ic
beha io (indica ed wi h a ows in Figu e 3c). The almos squa e hys e esis loops o he
GCMW
C
mic owi e wi h no malized emanen , M
, nea 0.96 indica es he axial cha ac e o
magne ic aniso opy wi h he easy axis o magne iza ion along he di ec ion o he applied
magne ic ield. Thus, he inc ease in
ρ
- a io a ec s he magne oc ys alline aniso opy, and
i s di ec ion has he same di ec ion o (220) and (420), as illus a ed in he s uc u al sec ion.
Howe e , in he sample GCMW
B
wi h a c ys alline s uc u e, non-pe ec ly squa e loops
a e obse ed. Such change in he hys e esis loop shape mus be ela ed o he p esence
o a conside able amoun o amo phous phase beside he diso de ed B2 o li le-o de ed
L2
1
s uc u es. In ou p e ious wo k a he same alloys, bu wi h a low
ρ
- a io (
ρ
= 0.26),
he enhancemen o he magne oc ys alline aniso opy, he squa eness, and coe ci i y o
Co
2
FeSi glass-coa ed mic owi es a e annealing was obse ed [
21
,
22
,
24
]. As we illus a ed
in ou p e ious wo k, he wo main ac o s a ec ing he magne ic aniso opy beha io
in Heusle -based glass-coa ed mic owi es a e uniaxial magne ic aniso opy and cubic
magne oc ys alline aniso opy [
21
,
22
,
24
]. By inc easing he
ρ
- a io, an enhancemen in
he c ys alline phase con en co ela es wi h he magne ic p ope y modi ica ion, i.e., he
main ac o con olling he magne ic aniso opy is he cubic magne oc ys alline aniso opy.
Un o una ely, cu en ly, we a e no able o measu e his ype o aniso opy expe imen ally,
bu he pe ec ly squa e loop indica es i s s ong e ec on he GCMW
B
and GCMW
C
samples. As seen in Figu e 4, he GCMWc sample shows he highes aniso opy ield
Senso s 2023,23, 5109 7 o 14
H
k
, coe ci i y H
c
, and no malized emnan M
. The odd beha io o H
k
is likely ela ed
o he big amo phous phase p esen in GCMW
A
and GCMW
B
samples, as he beha io
o Hc o hese wo samples is also qui e simila ( he e is no a dec ease, as in he case
o he H
k
, bu he alues a e almos he same) and maybe he g ow h o he c ys alline
s uc u e eases ini ially he educ ion o he aniso opy ield. In addi ion, he di e en ypes
o mic os uc u es (L21, B2, and A2) can also s ongly a ec he Hkbeha io .
Senso s 2023, 23, 5109 7 o 14
ield Hk, coe ci i y Hc, and no malized emnan M . The odd beha io o Hk is likely e-
la ed o he big amo phous phase p esen in GCMWA and GCMWB samples, as he beha -
io o Hc o hese wo samples is also qui e simila ( he e is no a dec ease, as in he case
o he Hk, bu he alues a e almos he same) and maybe he g ow h o he c ys alline
s uc u e eases ini ially he educ ion o he aniso opy ield. In addi ion, he diffe en
ypes o mic os uc u es (L21, B2, and A2) can also s ongly affec he Hk beha io .
Figu e 3. Room empe a u e hys e esis loops o Co2FeSi glass-coa ed mic owi es (a) GCMWA, (b)
GCMWB, and (c) GCMWC. The a ows in (c) pinpoin s he mul is ep magne ic beha io .
-200 -100 0 100 200
-1
0
1
M/M5K
Magne ic Fi eld ( Oe)
GCMW
C
(c)
-200 -100 0 100 200
-1
0
1
M/M5K
Magne ic Fi eld ( Oe)
GCMW
B
(b)
-200 -100 0 100 200
-1
0
1
M/M5K
Magne ic Fi eld ( Oe)
GCMW
A
(a)
Inc easing Aspec a io
0.3 0.4
0
26
52
78
0.51
0.68
0.85
1.02
70
84
98
112
Hc (Oe)
Hc
M
M
Hk (Oe)
H
k
Aspec a io
Figu e 3.
Room empe a u e hys e esis loops o Co
2
FeSi glass-coa ed mic owi es (
a
) GCMW
A
,
(b) GCMWB, and (c) GCMWC. The a ows in (c) pinpoin s he mul is ep magne ic beha io .
Senso s 2023,23, 5109 8 o 14
Senso s 2023, 23, 5109 7 o 14
ield Hk, coe ci i y Hc, and no malized emnan M . The odd beha io o Hk is likely e-
la ed o he big amo phous phase p esen in GCMWA and GCMWB samples, as he beha -
io o Hc o hese wo samples is also qui e simila ( he e is no a dec ease, as in he case
o he Hk, bu he alues a e almos he same) and maybe he g ow h o he c ys alline
s uc u e eases ini ially he educ ion o he aniso opy ield. In addi ion, he diffe en
ypes o mic os uc u es (L21, B2, and A2) can also s ongly affec he Hk beha io .
Figu e 3. Room empe a u e hys e esis loops o Co2FeSi glass-coa ed mic owi es (a) GCMWA, (b)
GCMWB, and (c) GCMWC. The a ows in (c) pinpoin s he mul is ep magne ic beha io .
-200 -100 0 100 200
-1
0
1
M/M5K
Magne i c Field ( Oe)
GCMW
C
(c)
-200 -100 0 100 200
-1
0
1
M/M5K
Magne i c Field ( Oe)
GCMW
B
(b)
-200 -100 0 100 200
-1
0
1
M/M5K
Magne i c Field ( Oe)
GCMW
A
(a)
Inc easing Aspec a io
0.3 0.4
0
26
52
78
0.51
0.68
0.85
1.02
70
84
98
112
Hc (Oe)
Hc
M
M
Hk (Oe)
H
k
Aspec a io
Figu e 4.
Aspec a io dependence on coe ci i y (H
c
), no malized emanence (M
), and in –plane
aniso opy ield (Hk) o Co2FeSi glass-coa ed mic owi es (lines o eye guide).
3.2.2. The momagne ic P ope ies
I is wo h no ing ha he e omagne ic ma e ials empe a u e s abili y is a c ucial
cha ac e is ic o hei possible applica ions in spin onic and sensing de ices. Hence, o a
wide ange o measu emen empe a u es, 5–350 K, we in es iga ed he magne ic beha io
o Co
2
FeSi glass-coa ed mic owi es wi h di e en
ρ
- a ios. The shape o he loops ollows
he same end obse ed a oom empe a u e: non-squa e o he GCMWAsample, qui e
squa e o he GCMW
B
one, and almos squa e o he GCMW
C
one (loops no shown).
In Figu e 5, he e olu ion o H
c
and M
wi h he empe a u e is shown. This beha io
demons a es ha o he GCMW
C
sample, cubic magne oc ys alline aniso opy p e ails
up o 350 K.
Senso s 2023,23, 5109 9 o 14
Senso s 2023, 23, 5109 8 o 14
Figu e 4. Aspec a io dependence on coe ci i y (Hc), no malized emanence (M ), and in –plane
aniso opy ield (Hk) o Co2FeSi glass-coa ed mic owi es (lines o eye guide).
3.2.2. The momagne ic P ope ies
I is wo h no ing ha he e omagne ic ma e ials empe a u e s abili y is a c ucial
cha ac e is ic o hei possible applica ions in spin onic and sensing de ices. Hence, o
a wide ange o measu emen empe a u es, 5–350 K, we in es iga ed he magne ic be-
ha io o Co2FeSi glass-coa ed mic owi es wi h diffe en ρ- a ios. The shape o he loops
ollows he same end obse ed a oom empe a u e: non-squa e o he GCMWA sam-
ple, qui e squa e o he GCMWB one, and almos squa e o he GCMWC one (loops no
shown). In Figu e 5, he e olu ion o Hc and M wi h he empe a u e is shown. This be-
ha io demons a es ha o he GCMWC sample, cubic magne oc ys alline aniso opy
p e ails up o 350 K.
Figu e 5. Tempe a u e dependence o he coe ci i y (a) and no malized emanence (b) o Co2FeSi
glass-coa ed mic owi es wi h diffe en aspec a io (lines o eye guide). The e o ba is as big o
smalle han he size o he symbols.
By analyzing he hys e sis loops measu ed a empe a u e ange, 5–350 K o Co2FeSi
glass-coa ed mic owi es wi h diffe en ρ- a io, an in e es ing magne ic beha io is ound
o bo h he empe a u e dependence o Hc and o he no malized emanence, M . GCMWC
sample shows he highes alue o he coe ci i y a he all measu ing ange o empe a u e
ange, wi h an a e age alue o Hc six imes highe han hose o he GCMW**, GCMWA
and GCMWB samples. GCMW**, GCMWA, and GCMWB samples show qui e simila al-
ues o he Hc whe e he diffe ence be ween he a e age alue o coe ci i y is abou 2 Oe.
By es ima ing he diffe ences in he coe ci i y (ΔHc) be ween he maximum alue o co-
e ci i y (Hc (max)) and he lowes alue o he coe ci i y (Hc (min)) o all samples, we p e end
o show i s s abili y wi h empe a u e. The samples wi h a clea c ys alline phase,
GCMW**, GCMWB, and GCMWC samples, show highe empe a u e s abili y han he
amo phous GCMWA sample. Hence, he ΔHc is 11 Oe, 3.5, and 9 Oe o GCMW**,
GCMWB, and GCMWC samples, espec i ely, whe eas ΔHc is 15 Oe o he GCMWA one.
The magne ic s abili y is clea e in he case o M endency wi h he empe a u e o
Co2FeSi glass-coa ed mic owi es wi h diffe en ρ- a ios. As shown in Figu e 5b, bo h
GCMWB and GCMWC samples show high s abili y wi h empe a u e, wi h ΔM 0.05 and
0.06, espec i ely (see Table 3). Meanwhile, he beha io o M o GCMWA is a he diffe -
en , compa ed o he o he samples wi h highe ρ- a ios, whe e a mono onic inc ease wi h
dec easing he empe a u e has been obse ed.
0 50 100 150 200 250 300 350
0
20
40
60
80
100
Hc (Oe)
T (K)
GCMWA
GCMWB
GCMWC
(a)
0 50 100 150 200 250 300 350
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
M
T (K)
GCMWA
GCMWB
GCMWC
(b)
Figu e 5.
Tempe a u e dependence o he coe ci i y (
a
) and no malized emanence (
b
) o Co
2
FeSi
glass-coa ed mic owi es wi h di e en aspec a io (lines o eye guide). The e o ba is as big o
smalle han he size o he symbols.
By analyzing he hys e sis loops measu ed a empe a u e ange, 5–350 K o Co
2
FeSi
glass-coa ed mic owi es wi h di e en
ρ
- a io, an in e es ing magne ic beha io is ound
o bo h he empe a u e dependence o H
c
and o he no malized emanence, M
. GCMW
C
sample shows he highes alue o he coe ci i y a he all measu ing ange o empe a u e
ange, wi h an a e age alue o H
c
six imes highe han hose o he GCMW**, GCMW
A
and GCMW
B
samples. GCMW**, GCMW
A
, and GCMW
B
samples show qui e simila
alues o he H
c
whe e he di e ence be ween he a e age alue o coe ci i y is abou
2 Oe. By es ima ing he di e ences in he coe ci i y (
∆
Hc) be ween he maximum alue
o coe ci i y (H
c (max)
) and he lowes alue o he coe ci i y (H
c (min)
) o all samples,
we p e end o show i s s abili y wi h empe a u e. The samples wi h a clea c ys alline
phase, GCMW**, GCMW
B,
and GCMW
C
samples, show highe empe a u e s abili y han
he amo phous GCMW
A
sample. Hence, he
∆
Hc is 11 Oe, 3.5, and 9 Oe o GCMW**,
GCMW
B,
and GCMW
C
samples, espec i ely, whe eas
∆
Hc is 15 Oe o he GCMW
A
one.
The magne ic s abili y is clea e in he case o M endency wi h he empe a u e o Co
2
FeSi
glass-coa ed mic owi es wi h di e en
ρ
- a ios. As shown in Figu e 5b, bo h GCMW
B
and GCMW
C
samples show high s abili y wi h empe a u e, wi h
∆
M
0.05 and 0.06,
espec i ely (see Table 3). Meanwhile, he beha io o M o GCMW
A
is a he di e en ,
compa ed o he o he samples wi h highe
ρ
- a ios, whe e a mono onic inc ease wi h
dec easing he empe a u e has been obse ed.
Table 3.
The geome ical pa ame e s and a e age (A .) o Co
2
FeSi glass-coa ed mic owi es wi h
di e en aspec a ios.
Sample ∆Hc(Hc (max) −Hc (min))∆M (M (max) −M (min))
GCMWA15 ±2 Oe 0.7 ±0.1
GCMW** 11 ±1 Oe 0.6 ±0.1
GCMWB3.5 ±0.5 Oe 0.06 ±0.01
GCMWC9±2 Oe 0.05 ±0.01
GCMW**: Co2FeSi glass-coa ed mic owi es wi h (ρ= 0.25) [24].
Figu e 6shows he comple e he momagne ic beha io o Co
2
FeSi glass-coa ed mi-
c owi es wi h di e en
ρ
- a ios. We pe o med he ZFC, FC, and FH magne ic empe a u e
dependence o check any possible phase ansi ion. Thus, he measu emen s we e pe -
o med a a low magne ic ield o 200 Oe. Fo he GCMW
A
sample, he ZFC, FC, and FH
magne iza ions cu es show non-homogonous beha io , besides an i e e sible magne ic
beha io a T = 150 K. Such i e e sibili y has been obse ed in ou p e ious wo k deal-
