P. PIETRUSIEWICZ et al.: THE INFLUENCE OF AN ISOTHERMAL ANNEALING PROCESS ON THE STRUCTURE ...
157–162
THE INFLUENCE OF AN ISOTHERMAL ANNEALING PROCESS
ON THE STRUCTURE AND MAGNETIC PROPERTIES OF THE
BULK AMORPHOUS ALLOY FeCoBYMo
VPLIV IZOTERMNEGA @ARJENJA NA STRUKTURO IN
MAGNETNE LASTNOSTI MASIVNE AMORFNE ZLITINE
FeCoBYMo
Pawe³ Pietrusiewicz1, Marcin Nabia³ek1, Jacek Olszewski1, Sabina Lesz2
1Czestochowa University of Technology, Institute of Physics, 19 Armii Krajowej Av., 42-200 Czestochowa, Poland
2Silesian Technical University, Institute of Engineering Materials and Biomaterials, Konarskiego St. 18a, 44-100 Gliwice, Poland
pietrusiewicz@wip.pcz.pl, pawelpietrusiewicz@wp.pl
Prejem rokopisa – received: 2015-06-30; sprejem za objavo – accepted for publication: 2015-12-24
doi:10.17222/mit.2015.151
This paper presents the results of research into a bulk amorphous alloy based on Fe. Samples with the composition
Fe61Co10Y8Mo1B20 were prepared in the form of plates using an injection-casting method. The samples were then subjected to an
isothermal annealing process (at less than the crystallization temperature) of 700 K for 1 h and 770 K for 3.5 h The structures of
the samples were investigated, both in the state after solidification and following the heat treatment, using X-ray diffraction
(XRD) and Mössbauer spectroscopy. The results confirmed that the samples, both after solidification and after annealing, were
amorphous. Magnetic measurements were carried out using a vibrating-sample magnetometer (VSM) with magnetic fields of up
to 2 T. Based on these measurements, the effect of the isothermal annealing process on the magnetic properties was defined,
including the saturation magnetization μ0Ms and coercive field Hc. Using the Kronmüller theory, the initial magnetization curves
were analysed in the area of approach to ferromagnetic saturation. On the basis of this theory, the quantity and quality of the
structural defects were defined; these defects play a critical role in the magnetization process in high magnetic fields. Following
this study, the sample annealed at 770 K for 1 h was found to feature a relatively low coercive field and the higher value of
magnetization saturation. Linear defects, the so-called quasidislocational dipoles, played the leading role in the process of
magnetization of the test samples.
Keywords: bulk amorphous alloys, structure, soft magnetic properties, defects
^lanek predstavlja rezultate raziskave masivne amorfne zlitine na osnovi Fe. Vzorci s sestavo Fe61Co10Y8Mo1B20 so bili
pripravljeni v obliki plo{~, s pomo~jo tla~nega litja. Vzorci so bili izotermno `arjeni 1 h (pri temperaturi ni`ji od temperature
kristalizacije) na 700 K in 3,5 h na 770 K. Preiskana je bila struktura vzorcev, v stanju po strjevanju in po toplotni obdelavi.
Uporabljena je bila rentgenska difrakcija (XRD) in Mössbauerjeva spektroskopija. Rezultati so potrdili, da so bili vzorci po
strjevanju in po `arjenju v amorfnem stanju. Magnetne meritve so bile izvedene s pomo~jo magnetometra z vibriranjem vzorca
(VSM) v magnetnih poljih jakosti do 2 T. Na osnovi meritev je bil dolo~en vpliv izotermnega `arjenja na magnetne lastnosti,
vklju~no z nasi~eno magnetizacijo μ0Ms in koercitivnim poljem Hc. Z uporabo Kronmüllerjeve teorije so bile analizirane za~etne
krivulje magnetizacije blizu podro~ja feromagnetnega nasi~enja. Na osnovi te teorije je bila dolo~ena koli~ina in kakovost
strukturnih napak; te napake igrajo klju~no vlogo pri procesu magnetizacije v mo~nih magnetnih poljih. Na podlagi te {tudije je
bilo ugotovljeno, da vzorci `arjeni 1 h ka`ejo relativno {ibko koercitivno polje in visoko vrednost nasi~ene magnetizacije.
Linearne napake, imenovane kvazi-dislokacijski dipoli, igrajo vodilno vlogo pri procesu magnetizacije preizku{anih vzorcev.
Klju~ne besede: masivne amorfne zlitine, struktura, mehko magnetne lastnosti, napake
1 INTRODUCTION
Amorphous soft magnetic materials are investigated
in many research centres around the world. These ma-
terials are characterized by a low coercive field and high
saturation magnetization.1–3 From a thermodynamic
point of view, the structure of these materials is meta-
stable. Nevertheless, such materials can be applied in
devices such as electronic measuring and surveillance
systems, magnetic wires, magnetic sensors, band-pass
filters, magnetic shielding, energy-saving electric power
transformers and other applications.4,5 During the past 20
years, intensive research has been conducted on amor-
phous alloy groups having a thickness or diameter
exceeding 100 μm; these are called bulk metallic glasses
(BMGs).6,7 These materials have good soft magnetic pro-
perties and a high mechanical strength.8
As mentioned previously, rapidly cooled amorphous
materials are thermodynamically unstable; they exhibit
instability in their physical properties with respect to
time and temperature. In general, their thermodynamic
stability can be improved by annealing for a specified
time at appropriate temperatures.9–12
As shown in the literature, the magnetic properties of
amorphous alloys depend strongly on the annealing tem-
perature.13–16 During the earlier sample production pro-
cess, free volumes are created; annealing the samples at
low temperatures leads to the diffusion of these free
volumes to the surface of the material. Thus, the soft
magnetic properties of these alloys can be improved
Materiali in tehnologije / Materials and technology 51 (2017) 1, 157–162 157
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
UDK 67.017:669.018.58:669-153:620.1 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 51(1)157(2017)
through the relaxation of internal stress, by annealing
them at less than the crystallization temperature.17
The paper presents results of structural and magnetic
studies concerning plate-shaped samples of the bulk
amorphous alloy Fe61Co10Y8Mo1B20. The investigated
material was subjected to two-stage annealing processes,
below the crystallization temperature.
2 EXPERIMENTAL PART
Samples of the composition Fe61Co10Y8Mo1B20 were
prepared in the form of plates using an injection-casting
method. These amorphous plates featured the following
dimensions: 10 mm width and 0.5 mm thickness. The
component chemicals, used in the production process,
were of high purity (~99.99 %). The ingots of alloy were
melted in an electric arc furnace. The crystalline ingot
and amorphous plate samples were prepared under a pro-
tective atmosphere of argon. The isothermal annealing of
the material samples took place in a vacuum furnace, in
order to prevent oxidation processes. Initially, a plate
sample was annealed at 700 K for 1 h and then at 770 K
for 3.5 h. The structure of the investigated material in the
form of a plate, in the state following solidification and
after annealing, was examined using a Bruker X-ray
diffractometer (XRD) equipped with a copper lamp
featuring a characteristic Cu-K radiation of wavelength
 = 0.154056 nm. The XRD studies were performed
within the angular range from 20° to 120° with a step of
0.01° and an exposure time of 7 s. In order to confirm
the amorphous structure of the examined samples, Möss-
bauer spectra were recorded using a Polon spectrometer
equipped with a 57Co source with an intensity of 50 mCi.
Static hysteresis loops were obtained using a Lake-
Shore vibrating-sample magnetometer (VSM) operating
in a magnetic field of up to 2 T. On the basis of these
measurements, the magnetization saturation (μ0Ms) and
coercive field (Hc) were determined, both for the heat-
treated samples and in the state following solidification.
Analysis of the initial magnetization curve was per-
formed in the area of the approach to ferromagnetic
saturation, according to the Kronmüller theory.18 On the
basis of this theory the authors specified the quantity and
quality of structural defects playing a decisive role in the
process of magnetization under the influence of strong
magnetic fields.
3 RESULTS AND DISCUSSION
Figure 1 shows the X-ray diffraction (XRD) patterns
of the Fe61Co10Y8Mo1B20 alloy in the states following
solidification and after annealing at two different tempe-
ratures.
The X-ray diffraction patterns, shown in Figure 1,
feature only one broad, blurred, maximum. This kind of
maximum occurs for the samples in the state following
solidification and after the isothermal annealing process.
These patterns are typical for materials featuring an
amorphous structure.
Figure 2 shows transmission Mössbauer spectra of
the amorphous Fe61Co10Y8Mo1B20 alloy plate samples in
the state following solidification and after annealing
firstly at a temperature of 700 K for 1 h and next at
770 K for 3.5 h. The spectra are expanded due to the
disorder of the atomic structure and small asymmetries.
The shapes of these spectra are typical for magnetic
alloys having an amorphous structure.19,20
Hyperfine field distributions P(B), obtained from
analysis of the Mössbauer spectra for all samples of the
Fe61Co10Y8Mo1B20 alloy (in the state following solidifi-
cation and after annealing), are shown in Figure 3.
These distributions are composed of two maxima. First,
the lower maximum Bef (of the average hyperfine field) is
in the 10 T field, and the second peak lies higher in the
23 T field. It is assumed that the first low-field peak is
associated with the nearest neighbourhoods of Fe and the
local presence of Y.21 The second peak corresponds to
the areas with less Fe, in which the 57Fe are partly
P. PIETRUSIEWICZ et al.: THE INFLUENCE OF AN ISOTHERMAL ANNEALING PROCESS ON THE STRUCTURE ...
158 Materiali in tehnologije / Materials and technology 51 (2017) 1, 157–162
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 2: The transmission Mössbauer spectra for the investigated
samples
Slika 2: Prenos Mössbauerjevega spektra preiskovanih vzorcev
Figure 1: X-ray diffraction patterns for powdered as-quenched,
annealed at 700 K/1h and 770 K/3.5h, plates
Slika 1: Rentgenogram zdrobljenih plo{~, ga{enih ter `arjenih 1 h na
700 K in 3,5 h na 770 K
surrounded by magnetic atoms (Co) and partly by
non-magnetic atoms (B, Mo).
From an analysis of Figure 3, it can be concluded
that post-production thermal treatment led to segregation
and the emergence of areas more or less rich in iron. The
data obtained from an analysis of the Mössbauer spectra
are summarized in Table 1.
Figure 4 shows the static magnetic hysteresis loops
for the samples in the state following solidification and
after heat treatment at different temperatures. These
hysteresis loops have a shape typical of materials with
soft magnetic properties. The data obtained from ana-
lysis of the static hysteresis loops, such as the saturation
magnetization (μ0Ms) and the coercive field (Hc), are
shown in Table 1.
Table 1: Data from analysis of the static hysteresis loops: μ0Ms –
magnetization, Hc – coercivity and the value of the mean hyperfine
field using the 57Fe nuclei (Bef) and the dispersion of the hyperfine
field distributions of the amorphous phase (Dam).
Tabela 1: Podatki iz analize stati~ne histerezne zanke: μ0Ms –
magnetizacija, Hc – koercitivnost in vrednost glavnega hiper {ibkega
polja z uporabo 57Fe nukleusov (Bef) in disperzijo razporeditve hiper
finega polja amorfne faze (Dam).
Sample μ0Ms Hc Bef (T) Dam (T)
as-cast 1.17 42 19.50(6) 5.13(8)
700 1.05 27 20.57(5) 5.78(5)
770 1.20 37 20.78(4) 5.50(5)
The initial magnetization curves were analysed
according to the theory of the approach to ferromagnetic
saturation proposed by H. Kronmüller and M. Fähnle18,
A. Neuweiler et al.22 and M. Hirsher et al.23 This theory
facilitates the extraction of information about the sources
of internal stresses occurring in the material, such as free
volumes and quasi-dislocation dipoles.18,22
Inhomogeneities affect the internal stress of the structure
and the process of magnetization in high magnetic fields.
An analysis of the initial magnetization curves enabled
the determination of the type of defects in the samples in
a state following solidification and after isothermal
annealing at the temperatures of 700 K and 770 K.
Figure 5 shows a šlinear-fit’ for the sample following
solidification, fulfilling the law of the approach to
ferromagnetic saturation (LAFS) as a function of (μ0H)–1
within magnetic fields ranging from 0.016 T < μ0H <
0.74 T. In contrast, for the sample after the isothermal
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Materiali in tehnologije / Materials and technology 51 (2017) 1, 157–162 159
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 3: The hyperfine field distribution on the 57Fe nuclei derived
from analysis of the transmission Mössbauer spectra (Figure 2) for
the investigated samples of Fe61Co10Y8Mo1B20 alloy
Slika 3: Hiper drobna razporeditev polja na 57Fe nukleusu, pridob-
ljena iz analize prenosa Mössbauerjevega spektra (Slika 2) pri
preiskovanih vzorcih zlitine Fe61Co10Y8Mo1B20
Figure 5: Magnetization as a function of (μ0H)–1 for a sample after
solidification and annealed at 700K for 1 h
Slika 5: Magnetizacija v odvisnosti od (μ0H)–1 za vzorec po strjevanju
in `arjenem 1 h na 700 K
Figure 4: Static hysteresis loops measured for tested samples in the
state following solidification (a), annealed at 700 K/1 h (b) and
annealed at 770 K/3.5h (c)
Slika 4: Stati~ne histerezne zanke izmerjene na vzorcih v stanju po
strjevanju (a), `arjeno 1 h na 700 K, (b) `arjeno 3,5 h na 770 K (c)
annealing process, at a temperature of 700 K for 1 h the
LAFS was fulfilled within the range of magnetic field of
0.017 T < μ0H < 0.72 T. This indicates that defects in the
form of quasi-dislocational dipoles are playing a decisive
role in the magnetization process (where the exchange
distance lH it is greater than the size of the dipole defect
Ddip (lH > Ddip)).18,22 For the sample annealed at 770 K for
3.5 h, the LAFS was fulfilled as a function of (μ0H)–2
(Figure 6) within the range from 0.16 T < μ0H < 0.61 T.
In this case, the decisive role in the process of magne-
tization is played by quasi-dislocational dipoles, for
which there is a relation lH < Ddip.
At higher fields, where structural defects did not play
a significant role in the magnetization process, the
magnetization of the material occurs by means of the
damping of thermally induced magnetic spin waves.
Figure 7 shows the linear fit of the magnetization as a
function of (μ0H)1/2, describing the Holstein-Primakoff
paraprocess.24 The following relationship was used in
Equation (1):
b g
D
kT g
spf
=
⎛
⎝
⎜
⎞
⎠
⎟354
1
40
3 2
1 2. ( )
/
/ 

B B (1)
where k – Boltzmann constant, μB – Bohr’s magneton,
g – gyromagnetic coefficient, calculated spin wave stiff-
ness parameter (Dspf).20 The calculated data, based on
the theory of approach to ferromagnetic saturation, is
summarized in Table 2.
Based on analysis of the data, presented in Table 2,
and in the papers 20,25,26, it can be concluded that the sam-
ple that was thermally treated at 700 K for 1 h featured
the most relaxed and homogeneous structure; this can
also be seen through an analysis of the results of the
magnetic and Mössbauer studies, presented in Table 1.
Table 2: Data obtained from analysis of the magnetization as a
function of the magnetic field, as powers of ½, 1, 2 and ½. Dspf – spin
wave stiffness parameter, Aex – exchange constant, lh – exchange
length, Ndip – density of quasi-dislocational dipoles (1) as-cast state,
(2) annealed 700 K, (3) annealed 770 K
Tabela 2: Podatki dobljeni iz analize magnetizacije, v odvisnosti od
magnetnega polja, v pristojnosti ½, 1, 2 in ½. Dspf – parameter togosti
spinskega vala, Aex – izmenjalna konstanta, lh – dol`ina izmenjave,
Ndip – gostota kvazi-dislokacijskih dipolov (1) lito stanje, (2) `arjeno
na 700 K, (3) `arjeno na 770 K
lp
B
(10–2T1/2)
Dspf
(10–2
meV nm2)
Aex
(10–12
J m–1)
lh
(10–9 nm)
Ndip
(1016
nm–2)
1 5.657(6) 45.11(6) 1.71(3) 2.24(3) 19.93(3)
2 4.333(2) 53.84(2) 1.86(3) 2.38(3) 17.61(3)
3 5.415(2) 46.41(2) 1.80(2) 2.48(2) 16.24(2)
4 CONCLUSIONS
In the case of crystalline materials, it is well known
that the structure is well described and can by charac-
terised by one primitive cell featuring a certain number
of atoms and angular translation. However, in the case of
amorphous materials, their structure hitherto has not
been completely characterised. In general, in the litera-
ture an amorphous structure is described as a metastable
system of randomly distributed atoms. The first sign of
changes in this structure is the process of nucleation of
the crystalline grains, which results in a material consist-
ing of two phases: the amorphous matrix and the fine
crystalline grains. Of course, the results of the inves-
tigations concerning amorphous materials that have been
subjected to an annealing process (below the crystallisa-
tion temperature) are presented in many papers. How-
ever, the description of the changes in the magnetic
parameters is limited only to changes in the exchange
interactions between the magnetic atoms.
In this paper, the "real" structure of an amorphous
alloy in the as-quenched state, and after two stages of the
P. PIETRUSIEWICZ et al.: THE INFLUENCE OF AN ISOTHERMAL ANNEALING PROCESS ON THE STRUCTURE ...
160 Materiali in tehnologije / Materials and technology 51 (2017) 1, 157–162
MATERIALI IN TEHNOLOGIJE/MATERIALS AND TECHNOLOGY (1967-2017) – 50 LET/50 YEARS
Figure 7: The Holstein-Primakoff para-process obtained for the
investigated alloy
Slika 7: Holstein-Primakoff paraproces pridobljen za preiskovano
zlitino
Figure 6: Magnetization as a function of (μ0H)–1 for a sample after
annealing at 770K for 3.5h
Slika 6: Magnetizacija v odvisnosti od (μ0H)–1 pri vzorcu `arjenem
3,5 h na 770 K
isothermal annealing, has been studied. An indirect
method of investigation has been used, which relies on
an analysis of the initial magnetization curves in the
LAFS region.18,27 Currently, this is the only known
method which facilitates a determination of the type and
volume of the structural defects present in the amor-
phous materials. These defects are the source of the
short-range structural defects and lead to non-collinear
distributions of the magnetisation in their vicinity, which
is directly reflected in the changes to the magnetisation
curve.
It is well known that annealing results in structural
relaxation. This can happen in two-ways: by conglome-
rating the free volumes to the linear defects or by releas-
ing free volumes to the surface. Therefore, a two-stage
annealing process was performed, at well-below the
crystallisation temperature (at 700 K and 770 K). This
resulted in structural relaxation through changes in the
density and the local chemical composition, leading to a
decrease in the number of centres of relaxation. It is
shown in the literature 14,28–31 that relaxations occur at the
atomic level, where the pre-exponential factor in the
Arrhenius law is in the order of 10–15.
The investigated plate-shaped samples of the
Fe61Co10Y8Mo1B20 alloy in the state following solidifi-
cation and after annealing at temperatures of 700 K and
770 K were found to feature an amorphous structure.
The magnetic studies showed that the annealing tem-
perature has a significant impact on the changes in the
magnetic properties. It was found that the sample
annealed at 700 K for 1 had the lowest coercive field,
Hc = 27 A/m. In contrast, the sample that was heat-
treated at 770 K for 3.5 h had the highest saturation
magnetization.
The results of the Mössbauer studies and the analysis
of the initial magnetization curve, in accordance with
Kronmüller theory, showed that thermal treatment at a
temperature of 700 K for 1 h caused the greatest homo-
genization of the structure of the samples. On the other
hand, for the investigated alloy in the form of plates
annealed at 700K for 1h, the decisive role in the process
of magnetization is played by defects in the form of
quasi-dislocational dipoles for which the relationship
lH > Ddip is satisfied. For the plate samples that were
annealed at 770 K for 3.5 h, the decisive role in the
process of magnetization is played by quasi-dislocational
dipoles for which there is a relationship lH < Ddip.
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