M. DOŒPIA£, M. NABIA£EK: INFLUENCE OF SOLIDIFICATION SPEED ON THE STRUCTURE AND MAGNETIC ...
823–827
INFLUENCE OF SOLIDIFICATION SPEED ON THE STRUCTURE
AND MAGNETIC PROPERTIES OF Nd10Fe81Zr1B6 IN THE
AS-CAST STATE
VPLIV HITROSTI STRJEVANJA NA STRUKTURO IN MAGNETNE
LASTNOSTI ZLITINE Nd10Fe81Zr1B6 V LITEM STANJU
Marcin Doœpia³, Marcin Nabia³ek
Czestochowa University of Technology, Institute of Physics, Armii Krajowej Av. 19, 42-200 Czestochowa, Poland
mdospial@wp.pl
Prejem rokopisa – received: 2015-07-01; sprejem za objavo – accepted for publication: 2015-09-15
doi:10.17222/mit.2015.174
The paper presents results of the structure and magnetic properties of the Nd10–xTbxFe81Zr1B6 (x = 0, 2) alloy in the as-cast state.
The samples were produced using the melt-spinning method. The solidification speed was controlled indirectly by changing the
linear velocity of a copper drum. Based on magnetic and structural studies, it was found that samples obtained while the linear
velocity of the copper drum was equal to 20 m/s had good hard-magnetic properties. The substitution of 2 % of Nd by Tb led to
grain growth of both the -Fe (9 nm and 24 nm for x = 0 and x = 2) and Nd2Fe14B phases (41 nm and 70 nm for x = 0 and x = 2,
respectively). The grain growth to sizes higher than the exchange interaction distance in the sample with Tb resulted in a
bimodal shape of the demagnetization curve. The samples obtained at higher linear speeds of the copper drum were composed
of amorphous matrices with small amounts of crystalline phases and had weak, soft-magnetic properties.
Keywords: permanent magnets, nanocomposities, X-ray diffraction, exchange interactions
^lanek predstavlja rezultate {tudije strukturnih in magnetnih lastnosti zlitine Nd10–xTbxFe81Zr1B6 (x = 0, 2) v litem stanju. Vzorci
so bili pripravljeni z ulivanjem na hitro vrte~em se valju. Hitrost strjevanja je bila posredno kontrolirana s spreminjanjem
linearne hitrosti bakrenega valja. Magnetne in strukturne {tudije so pokazale, da imajo vzorci, dobljeni pri linearni hitrosti
bakrenega valja 20 m/s, dobre trdomagnetne lastnosti. Nadomestilo z 2 % atomskega dele`a Nd s Tb, je povzro~ilo rast zrn obeh
faz -Fe (9 nm in 24 nm pri x = 0 in x = 2) in Nd2Fe14B (41 nm in 70 nm pri x = 0 in x = 2). Rast zrn, do velikosti, ve~je od
izmenjalne interakcijske razdalje v vzorcu s Tb, se je pokazala v bimodalni obliki demagnetizacijske krivulje. Vzorci, dobljeni
pri ve~jih linearnih hitrostih bakrenega valja, so bili sestavljeni iz amorfne osnove z majhnim dele`em kristalnih faz in so imeli
slabe mehko magnetne lastnosti.
Klju~ne besede: permanentni magneti, nanokompoziti, rentgenska difrakcija, izmenjalne interakcije
1 INTRODUCTION
Alloys based on rare earths, iron and boron are
currently some of the most popular groups of materials
with hard magnetic properties. These materials are
widely used in the electro-engineering industry. In recent
years, many scientific and industrial units have been
carrying out research on methods for curing their mag-
netic properties.1–5 The studies were mainly focused on
slight modifications to the chemical composition and
modifications to the production process parameters.
The most effective process, which guarantees repeat-
ability of the functional properties of produced alloys, is
producing amorphous ribbons and then tailoring their
properties by an appropriately matched heat treatment.6
However, the application of the heat treatment generates
additional costs. An alternative approach is solidification
of the liquid alloy with a slow speed. This leads to a
material with hard magnetic properties in the as-cast
state. A drawback of this method is the poor repeatability
of the functional parameters.
Modifications to the composition by a partial sub-
stitution of Nd by Tb can lead to two outcomes: if an
excess amount of Tb is used, it can result in the for-
mation of an amorphous matrix dividing the Nd2Fe14B
grains, thereby leading to a higher coercivity and also a
significantly reduced remanence;7,8 if smaller amounts of
rare earths with respect to the stoichiometric Nd2Fe14B
composition are used, it may result in the formation of
nanocomposites consisting of both Nd2Fe14B and -Fe
grains. The proper selection of the production process
parameters leads to grains of soft magnetic phase with
sizes similar or smaller than the exchange-interaction
length. This allows obtaining hard magnetic materials
with high saturation magnetization and a significant
remanence.8,9
Motivated by the above idea, we studied the influ-
ence of cooling rate on the curing of magnetic properties
and the structure of Nd10–xTbxFe81Zr1B6 (x = 0 and x = 2)
alloys, in the as-cast state, and the results of the study we
report in this paper.
2 EXPERIMENTAL DETAILS
The research material, i.e., Nd10–xTbxFe81Zr1B6 (x = 0,
2) melt, was obtained from components of the following
Materiali in tehnologije / Materials and technology 50 (2016) 5, 823–827 823
UDK 620.1:66.017:621.78 ISSN 1580-2949
Professional article/Strokovni ~lanek MTAEC9, 50(5)823(2016)
purity: Fe – 99.99 %; Zr – 99.99 %; Nd – 99.95 %, Tb –
99.95 %, B – 99.99 %. The crystalline ingots were seve-
ral times remelted to ensure the best mixing of elements
constituting the investigated material. Thin tapes were
produced by a unidirectional solidification of liquid
metal on a rotating copper cylinder, with three different
linear velocities (20, 30 and 35) m/s. The microstructure
of the samples, in the as-cast state, was examined using a
Bruker D8 Advance X-ray diffractometer with a charac-
teristic Cu-K radiation source (0.154056 nm). The
samples were scanned in the 2 angle range from 30° to
120° with a resolution of 0.02° and an exposure time of
3 s per step. Two samples were chosen for further analy-
ses, both qualitative and quantitative. Phase-composition
analysis was performed using the Rietveld method. The
magnetic studies were performed using a LakeShore
vibrating-sample magnetometer in an external magnetic
field up to 2 T. The demagnetization coefficient depen-
dent on the shape of the sample was not taken into
account. All the measurements were performed at room
temperature.
3 RESULTS AND DISCUSSION
Figure 1 shows the X-ray diffraction patterns ob-
tained for Nd10–xTbxFe81Zr1B6 (x = 0, 2) samples in the
form of tapes, in the as-cast state.
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824 Materiali in tehnologije / Materials and technology 50 (2016) 5, 823–827
Figure 1: X-ray diffraction patterns of: a) Nd10Fe81Zr1B6, b) Nd8Tb2Fe81Zr1B6 alloys obtained at different cooling rates, for samples in the
as-cast state
Slika 1: Rentgenska difrakcija: a) Nd10Fe81Zr1B6, b) Nd8Tb2Fe81Zr1B6 zlitin, dobljenih pri razli~nih hitrostih ohlajanja, za vzorce v litem stanju
Figure 2: Quantitative match of the phase composition obtained using the Rietveld refinement method for: a), c) Nd10Fe81Zr1B6, d), f)
Nd8Tb2Fe81Zr1B6 alloys solidified at 20 m/s linear velocity of copper drum, where a), d) experimental curve, b), e) matched pattern and c), f)
difference plot
Slika 2: Kvantitativno ujemanje sestave faz, dobljene z Rietveldovo metodo izpopolnitve: a), c) Nd10Fe81Zr1B6, d), f) Nd8Tb2Fe81Zr1B6 zlitini
strjeni pri linearni hitrosti bakrenega valja 20 m/s, kjer sta a), d) eksperimentalni krivulji, b), e) ujemanje in c), f) diagram razlik
In all the diffraction patterns obtained for the samples
cooled at higher rates, corresponding to the drum linear
speeds of 30 m/s and 35 m/s, at a 2 angle of about 43° a
broad, diffused halo characteristic for materials contain-
ing an iron-based amorphous phase is present. Also, it is
possible to distinguish the presence of narrower peaks
originating from small inclusions of crystalline phases.
Similar patterns were described in the literature as
semi-crystalline structures.10,11
The diffraction patterns of the samples solidified at a
drum speed of 20 m/s were composed of a number of
narrow peaks characteristic for a crystalline structure. In
this case, no diffused halo was observed, which indicates
the absence of any amorphous phase. A comparison of
the experimental diffraction peaks with the EVA data-
base let us conclude that two crystalline phases were
present in the sample: -Fe and Nd2Fe14B. These results
are in agreement with other reports concerned on
Nd2Fe14B alloys with an over-stoichiometric iron con-
tent.7,12–13
To ascertain quantitatively the phase compositions of
the samples without an amorphous matrix, Rietveld
analysis was performed (Figure 2), and the matching
results are summarized in Tables 1 and 2.
Table 1: The qualitative phase composition of Nd10–xTbxFe81Zr1B6
(where x = 0 or 2) samples solidified with the linear velocity of the
copper drum of 20 m/s, determined using the Rietveld refinement
method
Tabela 1: Kvalitativna sestava faz Nd10–xTbxFe81Zr1B6, (kjer je x = 0
ali 2), strjenih vzorcev z linearno hitrostjo bakrenega valja 20 m/s,
dolo~ena z uporabo Rietveldove metode izpopolnitve
Phase composition
Alloy -Fe (% vol) RE2Fe14B (% vol)
Nd10Fe81Zr1B6 19.15 80.85
Nd8Tb2Fe81Zr1B6 19.40 80.60
Table 2: Matching coefficients of the quantitative phase composition
of Nd10–xTbxFe81Zr1B6 (where x = 0 or 2) samples solidified with the
linear velocity of the copper drum of 20 m/s, determined using the
Rietveld refinement method
Tabela 2: Koeficienti ujemanja kvantitativne sestave faze
Nd10–xTbxFe81Zr1B6 (kjer je x = 0 ali 2) strjenih vzorcev z linearno
hitrostjo bakrenega valja 20 m/s, dolo~eno z uporabo Rietveldove
metode izpopolnitve
R – match parameters
Alloy Rp Rwp Rexp
Nd10Fe81Zr1B6 46.11 197.03 0.18
Nd8Tb2Fe81Zr1B6 44.15 192.79 0.11
The average grain size was determined on the basis
of Bragg’s equation for the 10 and 3 most intense peaks
of the Nd2Fe14B and -Fe, respectively:14
Δ hkl B
hkl
B
hklK
D
d
d
( ) cos( ) sin( )2 2 
 
⋅ =
⋅
+ ⋅ (1)
where D is the average grain size, K is a shape factor of
0.89,  is the X-ray wavelength, and hkl is the half-
width of the peak, d/d is the relative deformation of
the crystalline lattice and  B
hkl is the Bragg angle.
The above-presented equation describes the effect of
the grain size and the relative deformation of the cry-
stalline lattice resulting from diffraction-peak broad-
ening. This relationship is linear and the grain size is
determined from the intersection of the ordinate axis.
The average grain size of the -Fe and Nd2Fe14B pha-
ses was 9 nm and 41 nm, respectively, for Nd10Fe81Zr1B6,
and 24 nm and 70 nm for the alloy Nd8Tb2Fe81Zr1B6 for
samples solidified at a drum linear velocity of 20 m/s.
Due to the low intensity of the peaks originating from
the crystalline phases, for samples solidified at higher
linear velocities of the copper drum, the particle size was
not determined.
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Figure 3: The magnetic hysteresis loops and the initial magnetization curves for the: a), c) Nd10Fe81Zr1B6 and d), f) Nd8Tb2Fe81Zr1B6 alloys,
solidified at linear speeds of the copper drum equal to: a), d) 20 m/s, b), e) 30 m/s, c), f) 35 m/s
Slika 3: Magnetne histerezne zanke in za~etne krivulje magnetizacije pri zlitinah: a), c) Nd10Fe81Zr1B6 in d), f) Nd8Tb2Fe81Zr1B6 , strjenih pri
linearni hitrosti bakrenega valja: a), d) 20 m/s, b), e) 30 m/s, c), f) 35 m/s
Figure 3 shows the magnetic hysteresis loops and the
initial magnetization curves for all the studied samples.
From the analysis of the initial magnetization curves
and the main hysteresis loops the magnetic parameters,
such as coercivity (JHC), remanence (μ0MR) and satura-
tion of the magnetization (μ0Ms), were determined (Table
3). Additionally, for the materials with the best hard
magnetic properties the ratio MR/MS was also calculated.
It allows estimating the extent to which, in the nano-
composite, the phases with hard and soft magnetic pro-
perties are coupled by means of exchange interac-
tions.12,15,16 An additional indicator proving information
about the existence of such interactions in the nano-
composite comprising the phases of different magnetic
hardness can be the shape of the magnetic hysteresis
loop in combination with the results of the phase com-
position and grain size studies.15–17
Table 3: The basic magnetic parameters of the studied
Nd10–xTbxFe81Zr1B6 (where x =0 or 2) tapes in the as-cast state, deter-
mined from the initial magnetization curves and magnetic hysteresis
loops
Tabela 3: Osnovne magnetne lastnosti prou~evanih
Nd10–xTbxFe81Zr1B6 (kjer je x = 0 ali 2) trakov v litem stanju, dolo-
~enih iz za~etnih magnetizacijskih krivulj in magnetnih histereznih
zank
Linear
velocity v
(m/s)
coercivity
JHC
(T)
remanence
μ0MR
(T)
MR/MS
ratio
(a.u.)
Saturation of the
magnetization
μ0MS (T)
Nd10Fe81Zr1B6
20 0,7 0,82 0,77 1,06
30 9×10–4 – – 1,02
35 4×10–4 – – 1,15
Nd8Tb2Fe81Zr1B6
20 1,03 0,81 0,73 1,10
30 54×10–4 – – 0,81
35 13×10–4 – – 0,93
Based on the data collected in Table 3, it was found
that the material solidified at higher linear speeds of the
rotating copper drum (30 m/s and 35 m/s) was charac-
terized by poor, soft-magnetic properties, which was
related to the polycrystalline structure. Inclusions of
nanocrystalline grains in the amorphous matrix led to the
formation of additional pinning sites, which increases the
coercivity of the sample. Tapes produced with the lowest
cooling rates (20 m/s drum speed) were characterized by
good hard magnetic properties. The substitution of Nd
by Tb in the Nd10–xTbxFe81Zr1B6 alloy, quenched with the
lowest cooling rate resulted in an improvement of the
saturation magnetization and in a significant increase in
the coercivity. The increase in the saturation magneti-
zation was associated with a slightly higher content of
-Fe phase in the alloy composition.
The shape of the magnetic hysteresis loop of a
Nd10Fe81Zr1B6 sample with hard magnetic properties was
smooth, in spite of the presence of the two phases with
different magnetic hardnesses. Additionally, a high
MR/MS ratio (greater than 0.5) and a moderate grain size
of both phases are evidence of a strong coupling between
the grains of different phases, through exchange interac-
tions. The change of 2 % in the fractions of Nd by Tb in
the atomic composition, while maintaining the same
cooling rate, caused the formation of a bimodal shape of
the hysteresis loop. Juxtaposing this with the much larger
average grain size of both phases (almost two times
higher) and a lower MR/MS ratio, it can be concluded that
not all the soft magnetic -Fe grains were covered by ex-
change interactions. In this case, an increase in the
cooling rate by increasing the linear speed of the rotating
copper drum to 22 m/s should result in hardening of the
magnetic properties, because a Nd8Tb2Fe81Zr1B6 alloy
with smaller grain sizes would be obtained and phases
with different magnetic hardnesses would interact with
each other by exchange coupling.
The hysteresis loops for the samples solidified at
higher cooling speeds were of a wasp shape, typically
encountered in materials containing small inclusions of
hard magnetic phase distributed in the amorphous ma-
trix. The exception was the hysteresis loop obtained for
the Nd10Fe81Zr1B6 alloy that was solidified at the fastest
cooling rate. It had a typical shape characteristic for a
magnetically soft material. In this case, the low content
of crystalline phase only slightly affected the shape of
the hysteresis loop, mainly by increasing the coercivity
field (relative to a fully amorphous alloy).
4 CONCLUSIONS
On the basis of X-ray studies, it was found that the
samples made with the 20 m/s linear velocity of the
copper cylinder were crystalline and consisted of two
phases: -Fe and RE2Fe14B. A qualitative analysis of the
phase composition showed that the contents of both
phases were 19.15 and 19.40 of -Fe phase, 80.85 and
80.60 of Nd2Fe14B phase, for Nd10Fe81Zr1B6 and
Nd8Tb2Fe81Zr1B6 alloys, respectively. The grain size
analysis based on Bragg’s equation showed that the
grains in the alloy containing Tb were almost two times
larger. Alloys obtained with higher linear speeds of the
copper drum (30 m/s and 35 m/s) were mainly amor-
phous and contained only small amounts of crystalline
phase precipitates.
From the magnetic studies it was found that the tapes
produced with the lowest cooling rate were characterized
by the best hard magnetic properties. The application of
higher speeds of the copper drum resulted in their dete-
rioration.
The hysteresis loop of Nd10Fe81Zr1B6 (obtained at 20
m/s) was smooth due to presence of strong exchange
coupling between the phases of different magnetic hard-
ness. The substitution of Nd by Tb in these samples
resulted in an improvement of the saturation magne-
tization and in a significant increase in the coercivity, but
also resulted in the formation of a bimodal shape for the
hysteresis loop. The reason for this was decoupling of
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the exchange interaction due to an increase of the grain
sizes of both phases. Summarizing, for alloy with Tb
addition, an increase in the linear speed of the rotating
copper drum from 20 m/s to 22 m/s should result in a
hardening of the magnetic properties.
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