Development of Fe-Cu-Nb-Si-B

Based Nanostructure

for Soft Magnetic Properties

Presented by

Md. Khalid Hossain

Scientific Officer

Institute of Electronics

Atomic Energy Research Establishment

Bangladesh Atomic Energy Commission , Dhaka-1349

June 24, 2013

1

Lecture Outline

2

1. Fe-Based Soft Nanocomposite Magnetic Materials

2. Theoritical basis for magnetic softening

3. Importance of Nano-crystalline Alloys

4. Review of the Work on Nano-crystalline Alloy

5. Experimental

6. Result And Discussion

7. Conclusion

Fe-Based Soft Nanocomposite Magnetic Materials

An excellent soft magnetic property in nanocrystalline

alloys based on Fe-Cu-Nb-Si-B commercially known as

FINEMET was first discovered in 1988.

The major requirements for superior soft magnetic

properties are :

high initial permeability

extremely low coercivity

3

Theoritical basis for magnetic softening

Soft magnetic properties on the basis of Random Anisotropy Model

(RAM). According to this model, D = L / 3 .

Where, D= Grain ize

L= Exchange correlation length.

4

For bcc Fe-(20%Si) , L = 35 nm.

So, grain size D becomes 10 – 15 nm.

Therefore, grain size must be lies 10-15 nm for

Fe73.5Cu1Nb3Si13.5B9 nanocrystalline alloy.

Finemet has a low coercivity (Hc < 1 A/m) and high initial

permeability (µi ≈ 105).

Importance of Nano-crystalline Alloys

Nano-crystalline alloys play an important role in the

modern technology for it’s soft magnetic properties, i.e.

high saturation magnetization

high permeability

good frequency behavior

low losses

good thermal stability

reduction in size and

low weight

5

6

So nano-crystalline alloys are smart candidate in

telecommunication system.

Its also important in power transformer core where

high saturation induction and low hysteresis losses

are of principle importance.

Review of the Work on Nano-crystalline Alloy

The original alloy composition is Fe73.5 Cu1 Nb3.5 Si13.5 B9 .

Cu helps the nucleation of -Fe(Si)

Nb controls grain growth

Si and B has been used as glass forming materials.

7

Experimental

Amorphous ribbon of Fe73.5Cu1Nb3Si13.5B9 alloys

was prepared by melt- spinning method

Amorphousity, crystallization temperature, grain

size and composition of the grains were

determined by X-ray diffraction (XRD).

Annealing was performed in Muffle Furnace

Complex permeability was measured by an

Impedance Analyzer

8

From these X-ray spectra we observe that the crystallization

starts in the temperature 500-525°C, while at Ta = 700°C

very sharp peak (110) is obtained with large grain size. This

peaks are indexed as bcc Fe-Si phase.

Result And Discussion

9

The Lattice parameter of the bcc Fe-Si phase decreases with

increasing annealing temperature Ta up to 545°C and then the value

of lattice parameter increases up to annealing temperature 680°C.

2.82

2.83

2.84

2.85

2.86

2.87

450 500 550 600 650 700

Annealing temperature, Ta (° C)

La

ttic

e p

ara

me

ter,

(Å

)

10

% of Si with the increase of annealing temperatures and time

have the reverse effect in comparison with the effect of lattice

parameter

0

5

10

15

20

25

450 500 550 600 650 700

Annealing temperature, Ta (° C)

Sili

co

n (

at

%)

11

At 490°C the grain size is smaller in size, 7nm, and with the

increase of annealing temperature grain size is getting bigger

in size within the range of (823) nm.

0

5

10

15

20

25

450 500 550 600 650 700

Annealing temperature, Ta (° C)

Gra

in s

ize

, D

g (

nm

)

12

The initial permiability ( µ’ ) increases with anneling temperature upto 490°C then

decreases suddenly. Again initial permiability ( µ’ ) increases sharply passing

through a maxima at 545°C and then dramatically falls to very low value.

f = 1 kHz

0

5000

10000

15000

20000

25000

0 100 200 300 400 500 600 700

Ta (°C)

µ'

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0.0045

tan

δ/µ

'

initial permiability ( µ' )

relative loss factor ( tan δ/ µ' )

13

Permeability increases with annealing time attaining a maximum value at

30 min and than slightly decreases with longer annealing time possibly

due to induced anisotropy that develops due to longer holding time

Ta = 545 °C

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

22000

24000

26000

1 10 100 1000 10000

f (kHz)

µ'

5 min

10 min

30 min

35 min

40 min

45 min

60 min

14

Loss Factor

ta = 30 min

0

0.5

1

1.5

2

2.5

3

300 350 400 450 500 550 600 650

Ta (°C)

Lo

ss F

acto

r, D

2 kHz

3 kHz

4 kHz

5 kHz

50 kHz

Loss factor rapidly decreases with increasing annealing temperature

for various applied frequency (2-50) kHz. Loss factor has high value

at 50 KHz and decreases with the decrease of frequency.

15

Relative Quality Factor

For the sample annealed at 545°C for 30 minute give the maximum

quality factor if the applied frequency is lower i.e 10 kHz .

ta = 30 min

0

10000

20000

30000

40000

50000

60000

70000

300 350 400 450 500 550 600 650

Ta (°C)

Re

lati

ve

Qu

alit

y f

ac

tor,

µ'/

D

1 kHz

2 kHz

3 kHz

5 kHz

10 kHz

16

Magnetic Hysterisisgraph

ta = 30 min

-8

-6

-4

-2

0

2

4

6

8

-12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12

H (Oe)

B (

kG

)

Field dependence BH Loop of Fe73.5Cu1Nb3Si13.5B9

alloy which is annealed at 545°C for 30 minute.

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Coercivity (Hc)

Ta = 545°C

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 10 20 30 40 50 60 70Time (min)

Co

erci

vity

, Hc

( Oe

)

The coercivity is decreased if the annealing time is increased. But

in all the case the coercivity remain low (0.616 -0.406) oersted 18

Core losses

The core losses remain low (26.234 -17.752) W/kG if the

annealing time is in the range of 1 minute to 60 minute

Ta = 545°C

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70

Time (min)

Loss (

W /kG

)

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Remanence

The remanence is decreased if the annealing time is increased.

But in all the case the remanence remain low (3.224 -2.183) kG.

Ta = 545°C

0

0.5

1

1.5

2

2.5

3

3.5

0 10 20 30 40 50 60 70

Time (min)

Rem

anence, B

r (

kG

)

20

CONCLUSIONS

► X-ray diffraction results show that the grain size has

been obtained in the range of 7 nm to 21 nm at different

stage of annealing and Si content has been reached

upto 21.1 at %.

► When the alloy has been annealed for 30 minutes at

various temperatures, the maximum initial permeability

(μ') was observed at 545 0C.

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► For the annealing temperature of 545 0C best soft magnetic

properties has been achieved which corresponds to a

maximum value of initial permeability (μ') is 23,065 while the

corresponding value of relative loss factor is 4.002×10-5 at

fixed frequency f = 1 kHz.

► From Magnetic Hysterisisgraph is shown that, the Core

Loss is low (26.234 -17.752) W/kG, the remanence is low

(3.224 -2.183) kG and the Coercivity (Hc) is low (0.616 -0.406)

oersted, which is nothing but the good property of soft

magnetic materials. 22

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