Investigation on the crystallization mechanism difference between FINEMET® andNANOMET® type Fe-based soft magnetic amorphous alloysYaocen Wang, Yan Zhang, Akira Takeuchi, Akihiro Makino, and Yoshiyuki Kawazoe Citation: Journal of Applied Physics 120, 145102 (2016); doi: 10.1063/1.4964433 View online: http://dx.doi.org/10.1063/1.4964433 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/120/14?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Phase selection and nanocrystallization in Cu-free soft magnetic FeSiNbB amorphous alloy upon rapid annealing J. Appl. Phys. 119, 124903 (2016); 10.1063/1.4944595 Evolution of fcc Cu clusters and their structure changes in the soft magnetic Fe85.2Si1B9P4Cu0.8 (NANOMET)and FINEMET alloys observed by X-ray absorption fine structure J. Appl. Phys. 117, 17A324 (2015); 10.1063/1.4916937 Nano-crystallization and magnetic mechanisms of Fe85Si2B8P4Cu1 amorphous alloy by ab initio moleculardynamics simulation J. Appl. Phys. 115, 173910 (2014); 10.1063/1.4875483 Role of Si in high Bs and low core-loss Fe85.2B10−XP4Cu0.8SiX nano-crystalline alloys J. Appl. Phys. 112, 103902 (2012); 10.1063/1.4765718 Crystallization behavior and high temperature magnetic phase transitions of Nb-substituted FeCoSiBCunanocomposites Appl. Phys. Lett. 99, 192506 (2011); 10.1063/1.3660245

Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 210.72.19.207 On: Tue, 15 Nov 2016

11:23:19

Investigation on the crystallization mechanism difference betweenFINEMETVR and NANOMETVR type Fe-based soft magnetic amorphous alloys

Yaocen Wang,1 Yan Zhang,1,a) Akira Takeuchi,1 Akihiro Makino,2 and Yoshiyuki Kawazoe3,4

1Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan2Tohoku University, Sendai 980-8579, Japan3New Industry Creation Hatchery Center, Tohoku University, Sendai 980-8579, Japan4Kutateladze Institute of Thermophysics, Siberian Branch of Russian Academy of Sciences,630090 Novosibirsk, Russia

(Received 1 August 2016; accepted 25 September 2016; published online 11 October 2016)

In this article, the atomic behaviors of Nb and P in Fe-based amorphous alloys during nano-

crystallization process were studied by the combination of ab initio molecular dynamics simulations

and experimental measurements. The inclusion of Nb is found to be tightly bonded with B, resulting

in the formation of diffusion barrier that could prevent the over-growth of a-(Fe, Si) grains and the

promotion of larger amount of a-(Fe, Si) participation. The P inclusion could delay the diffusion of the

metalloids that have to be expelled from the a-(Fe, Si) crystallization region so that the grain growth

could be reduced with fast but practically achievable heating rates. The combined addition of P and

Nb in high Fe content amorphous alloys failed in exhibiting the potential of good magnetic softness

with slow heating (10 K/min) annealing at various temperatures. The sample with optimum crystalliza-

tion process with confined grain size was annealed at 653 K, with the grain size of 31 nm and a coer-

civity of �120 A/m, much too large to meet the application requirements and to be compared with the

currently well-studied alloy systems. This attempt suggests that the inclusion of early transition metal

elements might not be effective enough to suppress grain growth in crystallizing high Fe content amor-

phous alloys. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4964433]

I. INTRODUCTION

The study of Fe-based soft magnetic nano-crystalline

alloys is one of the hotspot in the research of magnetic mate-

rials. The absence of magneto-crystalline anisotropy and the

formation of inter-granular exchanged magnetic domains

based on random anisotropy model1 ensure the low coerciv-

ity and make this kind of materials very promising candi-

dates in the electric and electronic applications, which is

further encouraged by the development of FeSiBPCu nano-

crystalline alloy with considerably high saturation magneti-

zation (Bs).2,3

The nano-crystallized structure is usually obtained by

delicately annealing an amorphous alloy with optimized con-

ditions in terms of annealing time, annealing temperature,

and the heating rate, with the aim of acquiring sufficient

amount of a-Fe participation but confined a-Fe grain growth.

In the past few decades, various kinds of Fe-based nano-

crystalline alloys have been developed with good soft mag-

netic properties. The crystallization mechanism of them have

also been intensively studied for the purpose of better under-

standing and obtaining materials with better soft magnetic

properties. Particularly, the Kissinger plots and the Johnson–

Mehl–Avrami kinetic model are introduced to describe the

thermal activation and the progress of the crystallization pro-

cess.4–6 However, these theories along with their correlated

parameters might be good at characterizing the crystalliza-

tion progress, but the roles of the alloying elements along

with their interactions are yet to be analyzed and clarified so

that the fabrication of nano-crystalline alloys with better

properties could be practically improved in future.

Up to recent, most of the successfully developed Fe-based

nano-crystalline alloys have their composition formula as

FeXMCu,7–13 in which M represents one or more metalloids

such as Si and B, and X represents early transition metals

(ETM) such as Mo,7–9 Nb,10–13 Zr,14 and so on. The strategy is

to promote the nucleation of a-Fe by the addition of Cu12 and

inhibit the grain growth during the annealing process by the

addition of the ETMs.10–13 On the one side, the addition of Nb

was considered to be the most effective one,15 resulting in the

development of the Fe73.5Si13.5B9Nb3Cu1 soft magnetic nano-

crystalline alloy with the trademark of FINEMETVR

.

On the other side, without the inclusion of the ETMs that

are notorious for deteriorating Bs,16 the FeSiBPCu amorphous

alloy system known as the NANOMETVR

was also found to

be capable of generating large amount of a-Fe nano-crystals

under high heating rate during annealing, which would

greatly promote the saturation magnetization of the material

without deteriorating its low coercivity.2,3 By comparing with

the compositions of the other nano-crystalline materials, it is

easy to find out that P has played a crucial role in the grain

refinement during the annealing process.

However, despite the technological improvement, the

effect and role of P in the Fe-based amorphous alloys during

nano-crystallization process is not sufficiently understood.

In this article, the atomic behaviors of Nb and P in the

respective alloy systems were analyzed and compared with the

application of the ab initio molecular dynamics (AIMD) simu-

lations. Instead of the structural and thermal measurements

carried out by experiments, the AIMD simulation is able toa)Electronic mail: zy-jp@imr.tohoku.ac.jp

0021-8979/2016/120(14)/145102/6/$30.00 Published by AIP Publishing.120, 145102-1

JOURNAL OF APPLIED PHYSICS 120, 145102 (2016)

Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 210.72.19.207 On: Tue, 15 Nov 2016

11:23:19

show the chemical preference and the migration behavior in

atomic scale. Therefore, the effect and behavior of these ele-

ments in the multi-component alloy systems can be well-

analyzed and attributed to their physical and chemical origins,

so that the effect of these elements in various Fe-based amor-

phous alloys can be well-understood and predicted.

Experiments were also carried out to find out whether

the combined P-Nb addition could promote optimum nano-

crystallization in high Fe content amorphous alloy without

high heating rate annealing.

II. RESEARCH METHODS

A. Simulation methods

Vienna ab-initio simulation pack (VASP) was used to

perform the simulation works based on the density functional

theory. Interactions between particles were described with

projector augmented-wave pseudopotentials on the Perdew-

Burke-Ernzerhof type generalized gradient approximation

basis. Canonical ensemble was applied as the number of

atoms, the sampling volume, and the temperature were con-

figured. 200 atoms were sampled to simulate the amorphous

structures, and the sizes of the cubic sampling supercells

were determined according to the total weight of the atoms

and the experimentally-determined material density. The

temperatures were controlled by Nos�e thermostat.17–19 The

initial coordinates of the atoms in the simulated structures

were randomly assigned. Electron spins have been taken into

account throughout the simulation.

The following is the configuration to obtain amorphous

structures. The time interval for simulation was set to be 2 fs

for each MD step. In order to get amorphous structures, an

isothermal annealing was preliminarily performed at 1800 K

to remove any artificial factors in the initial structures. The

dimensions of the supercell during the isothermal annealing

started with 1.1 times of the normal size, and then shrank to

1.08, 1.06, 1.04, 1.02, and 1 times of the normal size after

every 2000 MD steps, which accounted for 12 000 MD steps

in all. In order to obtain room-temperature structures, cool-

ing process from 1800 to 300 K was adopted with 5000 MD

steps for every 200 K drop (above 1000 K) or every 100 K

drop (below 1000 K), corresponding to the cooling rates of

2� 1013 K/s and 1013 K/s, respectively. The slower cooling

rate for the latter stage was due to the consideration that cru-

cial phase transitions may take place below 1000 K. Finally,

another isothermal simulation was configured at 300 K for

2000 steps to reduce the possible effects brought by the

extremely high cooling rate.

Without specific description, the simulations for diffu-

sion study were performed at 1800 K to ensure the continu-

ous migration of the atoms.

B. Experimental methods

The sample fabrication, thermal analysis, crystallization

behavior, structural analysis, and evaluation of magnetic

properties were also performed in the present research. The

alloy ingots of Fe75.5Si13.5B9Nb1Cu1, Fe73.5Si13.5B9Nb3Cu1,

and Fe82Si4B8P2Nb1Cu1 (at. %) were prepared by arc-

melting with the mixtures of Fe (99.9 mass%), Nb (99.99

mass%), Cu (99.9 mass%), Si (99.9 mass%), B (99.5 mass%),

and pre-melted Fe3P (99 mass%). The prepared ingots were

used to fabricate amorphous ribbon samples by single-roller

melt spinning. Heat-treatments were performed by annealing

the amorphous ribbons in an infrared furnace at a heating rate

of 10 K/min. Magnetic property was measured by using a

B-H curve tracer. Thermal and structural analyses were per-

formed by using a differential scanning calorimetry (DSC)

and X-ray diffractometry (XRD), respectively. Here, grain

size of crystals referring to the XRD spectra is calculated by

using the Scherrer equation.

III. THE EFFECT OF Nb IN THE FINEMETVR TYPEAMORPHOUS ALLOYS

A. The diffusion of Nb in Fe-based amorphousstructures

Nb is chosen as a typical ETM in this study since it seems

to be the most effective one on reducing a-Fe grain growth

during the nano-crystallization process.15 In this part of inves-

tigation, ternary compositions of Fe70Si15Nb15 (FeSiNb),

Fe70B15Nb15 (FeBNb), and Fe70Cu15Nb15 (FeCuNb) with

amorphous structures are simulated to find out the structural

effect of Nb on crystallization process in the FINEMETVR

type Fe-based amorphous alloys.

In order to reveal the atomic interactions in Fe-based

amorphous alloys, the atomic diffusion ability is calculated

based on the measurement of the mean square displacement

(MSD) of the atoms according to the Einstein Diffusion

Equation20

MðtÞa ! 6Datþ Ba;

where M(t)a is the time dependent MSD of the element a, Da

is the corresponding diffusion coefficient, and Ba is a fluctua-

tion which can be omitted when large amount of atoms are

involved and large scale of diffusion time is considered.

To study the atomic behavior of Nb in Fe-based amor-

phous alloys, the MSDs of the elements in the FeSiNb,

FeBNb, and FeCuNb amorphous structures are calculated and

shown in Figs. 1(a)–1(c). It can be observed that the atomic

diffusion abilities of Nb in FeSiNb and FeCuNb alloys are

almost similar to that of Fe. Considering Nb is much larger

than Fe in atomic size, the similarity of diffusion abilities

between Nb and Fe suggests that the atomic size is no longer

the deciding factor for the diffusion ability in amorphous alloy

structures. However, on the other hand, by comparing the

behavior of Nb in FeBNb alloy and those in the other alloys,

the apparently smaller diffusion rate indicates that the exis-

tence of B can significantly inhibit the diffusion of Nb.

The diffusion behavior of the well-studied Fe73.5Si13.5B9

Nb3Cu1 amorphous alloy is also calculated and shown in

Fig. 1(d). It is well-expected that Nb in this alloy exhibits the

lowest diffusion activity. Moreover, the diffusion rate of B is

also smaller than that of Cu, indicating that the diffusion of

B has also been impeded by the Nb inclusion, since the small

atoms of B usually possess much larger diffusion ability than

the others such as Fe, Cu, Si, and so on.

145102-2 Wang et al. J. Appl. Phys. 120, 145102 (2016)

Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 210.72.19.207 On: Tue, 15 Nov 2016

11:23:19

Therefore, Nb and B are able to reduce the diffusion abil-

ity of each other when coexisting in the Fe-based amorphous

alloys, which will play crucial roles during the crystallization

process.

B. The bonding preferences in the FINEMETVR typeamorphous alloy

It is shown that the diffusion of Nb can be greatly inhib-

ited by coexisting with B in the FINEMETVR

type amorphous

alloys, which could be the reason for the reduced bcc Fe

grain growth in Fe-based nano-crystalline alloys. In order

to further reveal the mechanism for Nb to take effect on the

crystallization process, the atomic bonding preferences in the

Fe73.5Si13.5B9P3Cu1 amorphous alloy are also calculated [Fig.

2(c)] based on the integration of the partial pair-correlation

functions (PPCFs) as shown in Figs. 2(a) and 2(b).

It is common to find out that the chemical composition

surrounding the Fe atoms is almost the same as the nominal

alloy composition, and all the other atoms are surrounded by

compositions with larger Fe concentrations than the nominal

one, known as the solute-solute avoidance mechanism.21

However, the most interesting feature in Fig. 2(c) is the

bonding preference of Cu-Cu and Nb-B. It is clearly shown

that Cu has 15 at. % Cu neighbors, much larger than the

nominal Cu concentration of 1 at. %. Since there is no evi-

dence indicating strong bonding between Cu atoms, the local

concentration of Cu should be caused by the repulsion from

Fe-rich matrix and the sufficient redistribution owing to its

large diffusion ability. On the other hand, Fig. 2(c) also

shows that Nb concentration surrounding B is 5 at. %,

whereas B concentration surrounding Nb is 10 at. %, both of

which are larger than the nominal concentrations, providing

FIG. 1. Time dependent mean square displacements of the elements in (a)

Fe70Si15Nb15, (b) Fe70B15Nb15, (c) Fe70Cu15Nb15, and (d) Fe73.5Si13.5B9Nb3Cu1

amorphous alloys simulated at 1800 K.

FIG. 2. (a) Fe and (b) Nb involved Partial Pair Correlation Functions and (c)

Atomic bonding preference in the FINEMETVR

type Fe73.5Si13.5B9Nb3Cu1

amorphous alloy.

145102-3 Wang et al. J. Appl. Phys. 120, 145102 (2016)

Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 210.72.19.207 On: Tue, 15 Nov 2016

11:23:19

an evidence for the Nb-B bonding preference in Fe-based

amorphous alloys.

As a result, it can be confirmed from Fig. 2(c) that Nb

prefers to be bonded with B in the Fe-based amorphous

alloys, and the relatively firm chemical bonds could signifi-

cantly reduce the diffusion ability of both Nb and B, as

shown in Fig. 1.

Another issue arises when considering the binding

energy between the elements. As shown in Ref. 22, Nb and

B element pair does not exhibit significantly high binding

energy compared with other pairs such as Nb-Si or Nb-Cu.

The explanation may lie in the Fe-rich multicomponent envi-

ronments, which could make the atomic relationships of the

elements different from the binary situations.

In order to support this explanation, the binding energy

of the Nb atoms in the FeSiNb, FeBNb, and FeCuNb alloys

were calculated by measuring the increased system energies

after removing the Nb atoms from the simulated structures

while keeping the other atoms stationary. As a result, after

removing Nb atoms in each of the three alloys, the average

increments of the system energies are 9.3, 14.2, and 6.4 eV

for every removing Nb atom in the simulated Fe70Si15Nb15,

Fe70B15Nb15, and Fe70Cu15Nb15 amorphous alloys, respec-

tively, confirming that Nb and B in the Fe-rich alloy environ-

ment could exhibit much larger binding energy than the

Nb-Si and Nb-Cu pairs in the Fe-rich alloy system.

C. Discussion on the effect of Nb duringthe nano-crystallization process

According to the previous studies, Nb and B will form a

diffusion barrier near the surface of the growing a-(Fe, Si)

nano-crystals in the FINEMETVR

type amorphous alloy during

annealing so that the supply of Fe and Si from the amorphous

matrix will be inhibited and the over-growth of the crystalline

phase will be greatly prevented.10–13 The study shown in this

article confirms that Nb and B are preferred to be bonded

with each other with relatively firm chemical bonds.

However, according to the MSDs shown in Fig. 3, the

large atomic size does not give rise to the low diffusion abil-

ity of the Nb atoms in the FeSiNb and FeCuNb amorphous

structures. Instead, according to a previous study on atomic

diffusion in amorphous alloys,23 the binding energies of the

atoms will become the dominant factor on the atomic

diffusion in the amorphous structures; thus, the firm binding

between Nb and B in the FeBNb and FeSiBNbCu amorphous

alloys could greatly reduce the diffusion abilities of both Nb

and B atoms, resulting in limited grain growth during anneal-

ing process, as shown in the literature.

On the other hand, the Nb-B bonding preference could

bring benefits more than providing diffusion barriers. As

shown in Fig. 3, the differential scanning calorimetry (DSC)

curves of the Fe73.5Si13.5B9Nb3Cu1 and Fe75.5Si13.5B9Nb1Cu1

amorphous alloys were measured at a heating rate of 10 K/

min. Although the latter one (Fe75.5Si13.5B9Nb1Cu1) appears

to have larger Fe concentration of 75.5 at. %, it has a smaller

exothermic peak (54.3 J/g) that correlated to the early partici-

pation of a-(Fe, Si). It seems that the increased Nb concentra-

tion from 1 to 3 at. % has strong effect to promote the

fraction of a-(Fe, Si) participation.

From metallurgy point of view, it is well-accepted that

in the Fe-Si-B based amorphous alloys, the major crystalline

phases that to be formed during annealing is the a-(Fe, Si)

solid solution and the Fe-B compound phases. According to

the two steps crystallization shown in Fig. 3, with the help of

Cu, large amount of a-(Fe, Si) could be formed in early stage

of the crystallization and the others will be formed along

with the Fe-B phase in a eutectoid process. Therefore, with

less B concentration, the alloy will tend to form more a-(Fe,

Si) in the early stage.

In the Nb containing alloy, significant amount of B will be

trapped near Nb atoms and become less effective to support

the formation of Fe-B phase. Therefore, with relatively larger

concentration of Nb, the capacity of a-(Fe, Si) formation in the

first step will be enhanced. This effect has been verified in the

DSC curve in Fig. 3: larger amount of a-(Fe, Si) can precipi-

tate in the first crystallization step in the Fe73.5Si13.5B9Nb3Cu1

(low Fe concentration) amorphous alloy compared with the

Fe75.5Si13.5B9Nb1Cu1 (high Fe concentration) one.

IV. THE EFFECT OF P IN THE CRYSTALLIZATIONOF THE NANOMETVR TYPE AMORPHOUS ALLOYS

Among all the developed Fe-based soft magnetic nano-

crystalline alloys, the Fe85Si2B8P4Cu1 alloy known as the

NANOMETVR

alloy is one of the most successful alloys with

the combination of magnetic softness and large saturation

magnetization. Without the inclusion of Zr, Nb, or other early

transition metals, the inclusion of P could help to realize the

optimum nano-crystallization process with high heating rate

during annealing, which is quite different with the nano-

crystallization process for the FINEMETVR

alloy.

Based on the metallurgic knowledge and the previous

studies on atomic cluster analysis,23 both B and P have to be

excluded from the crystallizing region and dispersed into the

residual amorphous matrix during the formation and growth

of a-Fe grains in the Fe-based amorphous alloys. Therefore,

the a-Fe grain growth in the FeBP-based amorphous alloys is

greatly determined by the diffusion ability of B and P. In order

to have deep understanding on the diffusion of B and P in the

Fe-based amorphous alloys, simulations were performed on

the Fe70B15P15 amorphous alloy and the atomic diffusions of

B and P were calculated, as shown in Fig. 4.FIG. 3. Differential Scanning Calorimetry (DSC) curves of the Fe75.5Si13.5

B9Nb1Cu1 and Fe73.5Si13.5B9Nb3Cu1 amorphous alloys.

145102-4 Wang et al. J. Appl. Phys. 120, 145102 (2016)

Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 210.72.19.207 On: Tue, 15 Nov 2016

11:23:19

It is clearly shown in Fig. 4 that P exhibits much smaller

diffusion ability than B. During the crystallization of a-Fe, B

can be redistributed fast and easily owning to its significantly

high diffusion ability, which will hardly provide any preven-

tion on the growth of the grains, unless the temperature can

rise high enough to promote large amount of nucleation

within a short time against the diffusion dominated grain

growth. With the inclusion of P in the alloy, the formation of

a-Fe have to push P atoms into the amorphous matrix, but

the relatively low diffusion ability of P makes the growing

speed of the grains significantly limited. As a result, the tem-

perature can reach the optimum point for large amount of

nucleation in a relatively slower rate without concerning the

over growth of the early formed nuclei.

However, the diffusion ability of P is not low enough to

act as pinning site for grain growth; the optimum annealing

process for soft magnetic properties in NANOMETVR

type

amorphous alloys still requires high but practical heating

rate (e.g., 400 K/min).

V. DISCUSSION ON THE ATTEMPT OF P-NbCOMBINED ADDITION

Encouraged by the success in the development of

FINEMETVR

and NANOMETVR

alloys, attempts of P-Nb com-

bined addition in the Fe-based amorphous alloys were

reported in the literature, most of which were aimed to

develop a new alloy system that had much higher Fe concen-

tration than FINEMETVR

(73.5 at. %) and lower heating rate

for optimum nano-crystallization. However, there is still lack

of reliable evidence to show that the coexistence of Nb and

P could allow the Fe rich amorphous alloy to be properly

nano-crystallized without high heating rate annealing.

In order to clarify whether the combined addition of P

and Nb in high Fe content amorphous alloys can promote

nano-crystallization at low heating rate, amorphous alloy

with the composition of Fe82Si4B10P2Nb1Cu1 was prepared

in ribbon shape with the melt-spin technique. The X-ray dif-

fraction spectrum and DSC curve of the as-cast ribbon are

shown in Figs. 5(a) and 5(b), respectively. The annealing

temperatures were selected around the first initial crystalliza-

tion temperature [675 K from Fig. 5(b)] of the alloy with

an interval of 10 K to each other, with a heating rate of

10 K/min to reach the annealing temperatures. The isothermal

annealing processes were kept for 10 min and the samples

were then cooled under argon atmosphere. The XRD spec-

tra of these annealed samples were measured and also

shown in Fig. 5(a), and the grain sizes in these crystallized

samples were also calculated [Fig. 5(c)] referring to the

XRD spectra. Based on these XRD spectra, the grain sizes

in all the annealed samples are over 30 nm, much larger

than the typical grain sizes2,3,15 in the successfully annealed

alloys (<20 nm).

In fact, the coercivity of the sample annealed at 653 K,

which has its grain size measured to be 31 nm, is over

120 A/m, overwhelmingly far from the requirement for soft

magnetic applications.

Therefore, the attempt of Nb-P combined addition

reported in this article appears to be failed in achieving good

soft magnetic properties with slow heating annealing process.

The diffusion prevention effect of Nb during annealing might

be only significant with relatively low Fe concentration such

as the FINEMETVR

type Fe73.5Si13.5B9Nb3Cu1amorphous

alloy.

FIG. 4. Time dependent mean square displacements (MSDs) of B and P in

the Fe70B15P15 amorphous alloys simulated at 1800 K.

FIG. 5. Experimental properties of the Fe82Si4B8P2Nb1Cu1 melt-spun rib-

bons: (a) XRD spectra of the as-quenched and annealed samples; (b) DSC

curve of the as-quenched sample; and (c) Grain sizes of the samples

annealed at 643–693 K for 10 min at a heating rate of 10 K/min.

145102-5 Wang et al. J. Appl. Phys. 120, 145102 (2016)

Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 210.72.19.207 On: Tue, 15 Nov 2016

11:23:19

VI. SUMMARY

In this article, the effect of Nb in the FINEMETVR

type

amorphous alloys during nano-crystallization process is

extensively analyzed by the combination of AIMD simula-

tion and practical experiments. Despite the empirical under-

standings obtained before, the Nb is found to be functional

for nano-crystallization with the co-existence with B in this

type of alloys. Although the mixing enthalpy between Nb

and B is not so distinguishing, the binding energy of them in

the Fe-rich environment appears to be particularly large

compared with that between other atomic pairs. As a result,

Nb and B atoms exhibit significantly low diffusion ability by

the chemical interlocking, and the trapping of B also leads to

larger amount of a-(Fe, Si) participation at the first step of

crystallization.

On the other hand, the nano-crystallization mechanism

in NANOMETVR

type amorphous alloys is also studied, espe-

cially the effect of P, since it is the main compositional dif-

ference with the well-studied FINEMETVR

alloys. Unlike the

atomic interaction of Nb and B, the simulation shows that

the P atoms may take effect on their own, as they have to be

excluded from the crystallization regions like B, but exhibit-

ing much smaller diffusion ability than B in the Fe-rich

amorphous environment, which can slow down the grain

growth process. As a result, within a feasible heating rate

(e.g., 400 K/min), the NANOMETVR

type amorphous alloys

can be successfully nano-crystallized, with the additional

help of promotion of nucleation initiated by Cu.

Finally, in order to clarify the ambiguous results

reported in the literature on the effect of P and Nb addition

in high Fe content (>80 at. %) amorphous alloys, the

Fe82Si4B10P2Nb1Cu1 amorphous ribbon was prepared. The

measurements of the annealed sample suggest that the inclu-

sion of Nb in this alloy have little effect on preventing grain

growth since the annealing attempts with low heating rate

failed to refine the grain size for optimum soft magnetic

properties.

ACKNOWLEDGMENTS

This work was supported by JSPS KAKENHI Grant No.

15K18199, and the project of “Tohoku Innovative Materials

Technology Initiatives for Reconstruction” from the Ministry

of Education, Culture, Sports, Science, and Technology

(MEXT) of Japan.

The computational work was supported by Center for

Computational Materials Science (CCMS) in Institute for

Material Research (IMR) of Tohoku University with their

SR16000 supercomputer.

1G. Herzer, “Anisotropies in soft magnetic nanocrystalline alloys,”

J. Magn. Magn. Mater. 294, 99–106 (2005).2A. Makino, “Nanocrystalline soft magnetic Fe-Si-B-P-Cu alloys with high

Bs of 1.8–1.9T contributable to energy saving,” IEEE Trans. Magn. 48(4),

1331–1335 (2012).

3A. Makino, T. Kubota, K. Yubuta, A. Inoue, A. Urata, H. Matsumoto, and

S. Yoshida, “Low core losses and magnetic properties of Fe85-86Si1-2

B8P4Cu1 nanocrystalline alloys with high B for power applications,”

J. Appl. Phys. 109, 07A302 (2011).4K. Onoue, S. Kikuchi, T. Tanaka, M. Okada, and M. Homma, “Soft mag-

netic properties and finely crystallized structures in Fe-Mo-B amorphous

alloys,” J. Jpn. Inst. Metals 55(10), 1145–1150 (1991).5H. Okumura, D. E. Laughlin, and M. E. McHenry, “Magnetic and struc-

tural properties and crystallization behavior of Si-rich FINEMET materi-

als,” J. Magn. Magn. Mater. 267, 347–356 (2003).6A. Hsiao, M. E. McHenry, D. E. Laughlin, M. J. Kramer, C. Ashe, and T.

Ohkubo, “The thermal, magnetic, and structural characterization of the

crystallization kinetics of Fe88Zr7B4Cu1, an amorphous soft magnetic

ribbon,” IEEE Trans. Magn. 38(5), 3039–3044 (2002).7A. Hsiao, M. E. McHenry, D. E. Laughlin, M. R. Tamoria, and V. G.

Harris, “Magnetic properties and crystallization kinetics of a Mn-doped

FINEMET precursor amorphous alloy,” IEEE Trans. Magn. 37(4),

2236–2238 (2001).8C. F. Conde, J. M. Borrego, J. S. Blazquez, A. Conde, P. Svec, and D.

Janickovic, “Magnetic and structural characterization of Mo-Hitperm

alloys with different Fe/Co ratio,” J. Alloys Compd. 509(5), 1994–2000

(2011).9I. Kucuk, M. Aykol, O. Uzun, M. Yildirim, M. Kabaer, N. Duman, F.

Yilmaz, K. Erturk, M. V. Akdeniz, and A. O. Mekhrabov, “Effect of (Mo,

W) substitution for Nb on glass forming ability and magnetic properties of

Fe–Co-based bulk amorphous alloys fabricated by centrifugal casting,”

J. Alloys Compd. 509(5), 2334–2337 (2011).10H. Hermann, A. Heinemann, N. Mattern, and A. Wiedenmann,

“Experimental evidence for inhibitor-controlled mechanism of nanocrys-

tallisation in amorphous metallic alloys,” Europhys. Lett. 51(2), 127–132

(2000).11W. Lefebvre, S. Morin-Grognet, and F. Danoix, “Role of Niobium in the

nanocrystallization of a Fe73.5Si13.5B9Nb3Cu alloy,” J. Magn. Magn.

Mater. 301, 343–351 (2006).12P. Gupta, A. Gupta, A. Shukla, T. Ganguli, and A. K. Sinha, “Structural

evolution and the kinetics of Cu clustering in the amorphous phase of

Fe-Cu-Nb-Si-B alloy,” J. Appl. Phys. 110, 033537 (2011).13N. Mattern, A. Danzig, and M. Muller, “Effect of Cu and Nb on crystalli-

zation and magnetic properties of amorphous Fe77.5Si15.5B7 alloys,”

Mater. Sci. Eng. A 194, 77–85 (1995).14L. H. Kong, Y. L. Gao, T. T. Song, and Q. J. Zhai, “Structure and mag-

netic properties of Nb-doped FeZrB soft magnetic alloys,” J. Magn. Magn.

Mater. 323(16), 2165–2169 (2011).15Y. Yoshizawa, “Magnetic properties and microstructure of nanocrystalline

Fe-based alloys,” J. Metastable Nanocryst. Mater. 1, 51–62 (1999).16A. Makino, T. Kubota, C. Chang, M. Makabe, and A. Inoue, “FeSiBP bulk

metallic glasses with unusual combination of high magnetization and high

glass-forming ability,” Mater. Trans. 48(11), 3024–3027 (2007).17S. Nos�e, “A unified formulation of the constant temperature molecular

dynamics methods,” J. Chem. Phys. 81, 511 (1984).18S. Nos�e, “Constant temperature molecular dynamics methods,” Prog.

Theor. Phys. Suppl. 103, 1 (1991).19D. M. Bylander and L. Kleinman, “Energy fluctuations induced by the

Nos�e thermostat,” Phys. Rev. B 46, 13756 (1992).20J. Y. Qin, T. K. Gu, and L. Yang, “Structural and dynamical properties of

Fe78Si9B13 alloy during rapid quenching by first principles molecular

dynamic simulation,” J. Non-Cryst. Solids 355, 2333–2338 (2009).21H. W. Sheng, W. K. Luo, F. M. Alamgir, J. M. Bai, and E. Ma, “Atomic

packing and short-to-medium-range order in metallic glasses,” Nature 439,

419 (2006).22A. Takeuchi and A. Inoue, “Classification of bulk metallic glasses by

atomic size difference, heat of mixing and period of constituent elements

and its application to characterization of the main alloying element,”

Mater. Trans. 46(12), 2817–2829 (2005).23Y. Wang, A. Takeuchi, A. Makino, Y. Liang, and Y. Kawazoe, “Nano-

crystallization and magnetic mechanisms of Fe85Si2B8P4Cu1 amorphous

alloy by ab initio molecular dynamics simulation,” J. Appl. Phys. 117,

17B705 (2015).

145102-6 Wang et al. J. Appl. Phys. 120, 145102 (2016)

Reuse of AIP Publishing content is subject to the terms at: https://publishing.aip.org/authors/rights-and-permissions. Download to IP: 210.72.19.207 On: Tue, 15 Nov 2016

11:23:19