European Research and Training
Network
”Ductile BMG Composites”
Magnetic Properties of
Bulk Metallic Glasses
Paola Tiberto
INRIM, Torino
Outline
•
Magnetic Materials
Overview
Applications
•
Bulk Metallic Glasses
•
Hard and soft compositions
•
Nanocomposite Magnets
•
Recent Experimental data
•
Conclusions
Magnetic Effects of Electrons -- Domains
• Permanent magnetism is an atomic effect due to
electron spin. In atoms with two or more
electrons, the electrons are usually arranged in
pairs with their spins oppositely aligned → NOT
MAGNETIC
• If the spin does not pair → ferromagnetic
materials
m = −( e / 2me )⋅ L
m =i⋅A
-e
v
i
i
L
me
Domains
• Large groups of atoms in which the
spins are aligned are called domains
• When an external field is applied,
the domains that are aligned with
the field tend to grow at the expense
of the others.
material becomes magnetized
Domains
• (a)
Random
alignment
shows
an
unmagnetized material
• (b) When an external magnetic field is
applied, the domains aligned parallel to
external magnetic field grow
Ferromagnetic materials
Hysteresis loop
H=0
H = Hmax
B= µ0(H + M) = µ0H + J
H=0
Types of Ferromagnetic Materials
•Two categories:
a)Soft magnetic materials
•i.e. Fe: easily magnetized
If the external field is removed, magnetism
disappears
Hc < 10 A/m
b) Hard magnetic materials
• Co and Ni: difficult to magnetize
–They tend to retain their magnetism
Permanent magnets
Hc > 100 A/m
Hysteresis Loops
SOFT magnetic materials
A small amount of dissipated
energy in repeated
Reversing magnetisation
HARD magnetic materials
Retains a large
fraction of the saturation field
when H is removed
M
Transformers
Motor cores
permanent magnets,
memory devices
Magnetic recording
Ferromagnetic Materials
Magnetic materials are widely used in modern devices
for their ability to produce or to amplify a magnetic
field in the outer space.
•SOFT magnetic
•HARD magnetic
easy to magnetise
difficult to demagnetise
provide great amplification of
magnetic field produced by
electric current in a coil
provide
a
source
of
magnetic field without
power supply
Ferromagnetic materials
Soft Magnetic materials
• Shape of the M,H (or B,H) curve affected by magnetic
anisotropy K:
K magnetic properties depend on the
direction in which they are measured.
• K is exploited in the design of most magnetic materials
of commercial importance.
Soft and extra-soft magnetic properties: low values of the
magnetic anisotropy (K in the range of few ten J/m3 and less, i.e.
Fe-Ni alloys).
Vanishing anisotropy can be obtained in amorphous and
nanocrystalline alloys, because the structural order in these
materials is extended over limited distances, from few atomic
spacings to few nanometers.
Soft Magnetic materials
High saturation magnetisation
Low magnetocrystalline anisotropy
Low coercive field
High magnetic response
Easy and fast attain of saturation
Easy magnetic domain wall movement
(homogeneous material without difects,
inclusions, stress …)
High Curie Temperature
High electrical resistance
Magnetic stability at higher temperatures
Minimise magnetic losses due to Eddy
currents
Non-expensive
For application in devices on large scale
Soft Magnetic materials
Composition: values of saturation magnetization Ms, the
magnetic anisotropy constants K and the magnetostriction
constants
magnetization process related to the material
structure (e.g. crystallographic texture, grain size,lattice
defects, etc.).
Proper choice of composition and suitable metallurgical and
thermal treatments allow to obtain extra soft magnets (Hc≈
0.1 A/m and µ0 ≈ 106).
A number of additional properties, like thermal and structural
stability, stress sensitivity of the magnetic parameters,
mechanical
properties
and
machinability,
thermal
conductivity have to be considered.
The final acceptance of a material in applications will result
from a cost-benefit evaluation of all these properties.
Soft Magnetic materials
Composition
µmax
Hc (A/m)
Js (T)
----------------------------------------------------------------------------------------------------------Fe100
3-50⋅⋅103
1-100
2.16
Fe
NO Fe-Si
Fe(>96)-Si(<4)
3-10⋅⋅103
30-80
1.98-2.12
GO Fe-Si
Fe97-Si3
20-80⋅⋅103
4-15
2.03
Fe-Si 6.5%
Fe93.5-Si6.5
5-30⋅⋅103
10-40
1.80
Sintered
powders
Permalloy
Fe99.5-P0.5
0.2-2⋅⋅103
100-500
1.65-1.95
Fe16-Ni79-Mo5
5⋅⋅105
0.4
0.80
Permendur
Fe49-Co49-V2
2⋅⋅103
100
2.4
Ferrites
(Mn,Zn)O⋅⋅Fe2O3
3⋅⋅103
20-80
0.2-0.5
Sendust
Fe85-Si9.5-Al5.5
50⋅⋅103
5
1.70
Amorphous
(Fe-based)
Fe78B13Si9
105
2
1.56
Amorphous
(Co-based)
Co71Fe4B15Si10
5⋅⋅105
0.5
0.86
1
1.2
NanocrystallineFe73.5Cu1Nb3Si13.5B9 105
Hard magnetic materials
Hard magnets are used for their ability to produce a
static magnetic field in the outer space without need
of electric power and without heat dissipation.
Three relevant quantities are used to describe
their performances:
• Coercive field, Hc
• Remanent
magnetisation, Mr
• Maximum Energy
Product, (BH)max
B= µ0H + µ0M
Coercivity
Expresses the ability of the magnetic material to retain
its magnetised state
The magnetisation reversal occurring in the 2nd
quadrant of the M:H loop may be strongly hindered by:
the magnetic
phase intrinsic
ANISOTROPY
AND/OR
Fe14Nd2B
M
M
the material
MICROSTRUCTURE (grain
size, defects, precipitates...)
Original
magnetisation
Reversed
magnetisation
Domain wall
Pinning centre
Materials for permanent magnets
(BH)max has doubled
every 12 years in XX
century
Increase in (BH)max =
decrease in size and
weight of devices
Now reached a plateau value
with NdFeB magnets based
on the intermetallic
compound:
Fe14Nd2B
Intrinsic limitation:
(BH)max≤ µ0Ms2/4
magnetite
ferrite
NdFeB
Applications: Hard Magnets
• 60% of NdFeB magnet production goes into disc-drive applications,
primarily voice-coil-motors (VCMs).
• very wide range of applications for RE-magnets:
1. Automotive: modern cars ≈ 100 permanent magnet motors.
Currently these are almost exclusively based on Sr-ferrite (SrFe12019)
and the penetration of NdFeB magnets into this area requires a
significant cost reduction, an increase in the maximum operating
temperature and improvement in corrosion resistance.
2.“white goods”: washing machines, refrigerators to improve energy
efficiency and hence reduce CO2 emissions
using NdFeB magnets would be a significant reduction in
volume and weight and an improved efficiency.
Ferromagnetic BMG
• Non-optimal properties and uses of electromagnetic materials in various devices and
appliances.
• Improved energy efficiency: 1% total electrical
energy produced in the US lost as heat
dissipated by distribution transformers that use
ferromagnetic cores made from amorphous
glassy materials (20 -40 µm thick)
• Limitation of efficiency: post-anneal brittleness,
stress sensitivity
• Quest for materials having simultaneously high
glass forming ability, superhigh strength and
excellent magnetic properties.
Bulk Metallic Glasses
• 1951: Amorphous metallic materials
unique electronic
and mechanical properties arising from a lack of long-range
crystallographic order. Produced by means of
rapid
solidification techniques (melt-spinning and splat-cooling)
with extreme quenching conditions, typically exceeding 106
K/s.
• 1974: BMG certain metallic alloys can be vitrified into a
completely amorphous state from the liquid at cooling rate
of 10 K/s .
•Late eighties: BMG alloys may be cast into rods up to 2 cm
or more in diameter and have technological potential due to
netshape forming.
forming
Ferromagnetic BMG: chronology
• Before 1993: no room-temperature ferromagnetic BMG
• 1995: Inoue
containing a
compositions
(P,B,Si).
et al. Produced ferromagnetic BMG alloys
very large number of elements. Typical
Fe–(Al,Ga)–(P,C,B,Si) and Co–Cr–(Al,Ga)–
•1996 Inoue et al. developed BMG rods (1–12mm
diameter) of composition RE60Fe30Al10 (RE=Nd or Pr) with
appreciable coercivities at room temperature (HARD).
• Relatively difficult to cast: critical cooling rate of 102
÷103 K/s,
K/s higher than 1 ÷ 10 K/s characteristic for alloys
with very good GFA, limiting the maximum achievable
diameter to a few millimeters.
•Other Hindrance: presence of impurities in the melt, or
of crystalline inclusions that can form upon solidification
of the melt.
Ferromagnetic BMG
Ferromagnetic BMG
Ferromagnetic BMG
• Amorphous Fe-Al-Ga-P-C-B cast cylinders: Hc ≈ 10 A/m
and a Js ≈ 1.1 T compare with those of conventional FeSi-B-based amorphous ribbons without the appreciable
degradation observed for thick samples (i.e. . A. Inoue,
Acta Mater. 48 (2000) 279)
• Ultrahigh strength (5 GPa) Co43Fe20Ta5.5B31.5 bulk glassy
alloy.
Ring (thick 1 mm, d = 7 and 3 mm): Hc = 0.25 A/m and µm =
5.5 105 Js = 0. 49 T.
Softness related to glassy structure with high homogeneity
level and absence of crystalline nuclei (A. Inoue at al.,
Nat. Mat. 2 (2003) 661)
• Nd,Pr-Fe-based BMG’s, containing ultra-fine dispersions
of nanocrystals, have moderately high Hc (2.5 105 A/m).
Ferromagnetic BMG
Fe- and Co-based glassy alloys have similar
combination of lower coercivity and higher electrical
resistivity among all soft magnetic metallic alloys. The
lower coercivity is presumably due to the smaller
magnetic anisotropy and lower internal stress.
Soft magnetic BMG
Soft magnetic BMG
(Fe0.6Co0.4)72Si4B20Nb4
glassy
plates used for the magnetic
yoke of linear actuator (devices
which transform an input signal).
Js = 1.15 T and µmax= 73000.
Soft magnetic BMG
Hard magnetic BMG
• BMG rods (1–12mm diameter) of composition RE60Fe30Al10
(RE=Nd or Pr) with appreciable coercivities (about 0.4 T) at
room temperature
nanocomposite structures nanocrystallites embedded in
the amorphous matrix
• These microstructures have been shown to improve the soft
or hard magnetic properties in ribbons, respectively by
controlled crystallisation of an initially amorphous alloy or
by casting under controlled conditions (i.e. FINEMET,
Exchange Spring).
• A major hindrance: inherent brittleness induced during the
development of a nanocrystalline phase.
• The use of BMG precursors facilitates the direct casting not
only of toroidal but also more complex shapes which can
then be annealed to nanocomposite structures with
exchange enhanced properties
Nanocomposite Magnets
• Uniform mixture of exchange coupled magnetically hard
and soft phases : High energy products and relatively high
coercivities
•Advantages: high reduced remanence, mr (= Mr/Ms) and
low material cost due to the reduction in the content of the
expensive hard magnetic phase.
•A small grain size (10-20 nm) and a uniform mixture of the
two phases is a prerequisite for exchange coupling. This
coupling leads to a smooth hysteresis loop in which the
individual character of the constituent phases is concealed.
•Suitable microstructure is most conveniently handled
through non-equilibrium metallurgical techniques such as
melt-spinning, mechanical alloying, and sputter deposition.
The ternary system Nd-Fe-Al
This ternary alloy system:
• Exhibits amorphous formation
in a wide composition range:
• Shows good hard magnetic
properties (i.e. high
coercivity) at RT in the
amorphous state
• Has a low critical cooling rate for
glass formation, suitable for Bulk
Metallic Glasses (BMG) preparation
Origin of coercivity in NdFeAl BMG
Observation:
Hard behaviour associated with a nominally amorphous (at XRD)
phase developed under moderate cooling conditions
Proposed explanations:
•
RANDOM ANISOTROPY MODEL: exchange coupling among
magnetically ordered (Fe-rich) clusters with large random
magnetic anisotropy
•
PINNING MODEL: impediment to domain wall motion
due to non-magnetic (Nd-rich) nanoparticles acting as
pinning centres
•
PRESENCE OF ANISOTROPIC PHASES : ternary equilibrium µ phase
or the binary Fe-Nd metastable A1
Hard magnetic BMG
The high coercivity can arise
from impediments to domain wall
motion, caused by grains
boundaries, surfaces, or magnetic
inhomogeneities.
Research Objectives
evaluate the effects of different quenching
rates on magnetic properties of the alloy:
Nd70Fe20Al10
and relate microstructural
features with magnetic hysteresis
?
Production techniques
Nd70Fe20Al10
ARC MELTING
AM bulk ingot
COPPER MOULD
CASTING
PLANAR FLOW
CASTING
CM cone
Ribbon
Studied samples
Arc melted master alloy
AM sample
CM sample 1
CM sample 2
2 Copper mould cones
2 Rapidly solidified ribbons
RS ribbon 1
RS ribbon 2
Sample A
2 Crystalline samples
Sample E
(master alloy
annealed at 580°C)
(prealloy solidified
under equilibrium
conditions)
- despite the claimed large GFA
crystallisation cannot be avoided
- hcp-Nd + additional reflections:
(1 1 4)
(1 1 0)
(1 0 3)
(1 0 6)
hcp-Nd calc.
(1 0 1)
(0 0 4)
Intensity (arbitrary units)
(1 0 2)
Structural characterisation
@ Nd3Al, for AM and CM samples;
# ternary δ phase (Nd6Fe13-xAl1+x)
for AM master alloy
- broad amorphous halo in RS ribbons
@
@#
@
@
AM sample
@
CM sample 2
CM sample 1
RS ribbon 2
RS ribbon 1
2.0
2.5
3.0
3.5
4.0
-1
Wavevector S [Å ]
4.5
- grain size for Nd crystals:
RS ribbons
CM cones
AM master alloy
~10 nm
~30 nm
~40 nm
Residual amorphous phases with
different elemental composition:
quenching
Nd70Fe20Al10 → x Nd + (1-x) Am
Thermal behaviour
Temperature [K]
- An amorphous phase is
formed in all samples
regardless of the quenching
rate;
- no evidence of Tg but
additional exothermic signal
present at T< Tx due to the
growth of Nd precipitates.
650
700
750
800
850
EXO
100 mW/g
Tx = 531°C
AM master alloy
Tx = 505°C
CM 2
Heat flow
- Onset crystallisation
temperatures (Tx) increase
with the decrease of the
quenching rate;
600
Tx = 486°C
CM 1
Tx = 475°C
RS 2
Tx = 453°C
RS 1
300
350
400
450
500
550
Temperature [°C]
An amorphous phase can be easily developed under moderate
cooling rates, such as in the arc melting equipment. Its
composition is determined by the amount and stoichiometry of
crystalline phases precipitated during the solidification process.
Magnetic behaviour
• All samples are
ferromagnetic at RT;
• heat treatment above Tx
causes collapsing of
hysteresis loop into a
paramagnetic response
-1000
-500
500
1000
0.05
J [T]
• Coercive fields increase
with the decrease of the
quenching rate;
0.10
H [kA/m]
0
annealed
0.00
on
RS ribb
-0.05
-0.10
-15000
mple
CM sa
mple
AM sa
-10000
-5000
0
5000
10000
H [Oe]
•HARD PROPERTIES depend on the presence
of the AMORPHOUS PHASE;
•none of the CRYSTALLINE EQUILIBRIUM
PHASES is FERROMAGNETIC at RT
15000
Magnetic behaviour/bulk samples
H [kA/m]
0
500
1000
0.10
5
Hc = 87 kA/m
0.05
Hc = 256 kA/m
0
0.00
Hc = 160 kA/m
-5
-0.05
AM sample
CM sample1
-10
-15000
J [T]
•highest coercive field
develops in the slowest
cooling conditions
-500
10
M [emu/g]
•Magnetic properties are
extremely sensitive to
quenching conditions;
-1000
CM sample 2
-10000
-5000
0
5000
10000
-0.10
15000
H [Oe]
•Absolute values of Mmax and Mr depend on composition of
the ferromagnetic phase and not only on its volume fraction
•All hysteresis loops don’t reach saturation at the maximum
applied field
Magnetic behaviour/bulk samples
No saturation is reached at the maximum applied field
0.10
-1500 -1000
-1000 -500
-500
H (kA/m)
(kA/m)
H
500
00
500
1500
2 magnetic
contributions:
aa 10
0.10
10
b
0.05
0.05
5
5
b
c 0
0
0.00
0.00
M
M (emu/g)
(emu/g)
JJ (T)
(T)
1000
1000
-5
-5
-0.05
-0.05
-10
-0.10
-10
-0.10
-20000
-15000-10000-5000
-15000
-10000 -5000
00
H (Oe)
(Oe)
H
5000
20000
5000 10000
1000015000
15000
•FERROMAGNETIC
contribution due to the
amorphous phase
•PARAMAGNETIC
contribution due to the
precipitated phases
Magnetisation is saturated after subtraction
Hard behaviour isn’t related to high anisotropy
Origin of coercivity in bulk samples
•No evidence of definite hard
magnetic phases like A1 or µ
phase
•first magnetisation curve:
PINNING type BEHAVIOUR
of the magnetisation process
•coercivity independent on
the formation of Nd crystals
evidenced by SEM and XRD
-500
0
500
0.08
5
0.04
0
0.00
-5
-0.04
-10
-10
mple
AM sa
-5
J (T)
10
M (emu/g)
•coercivity
due
to
paramagnetic
nanoparticles,
embedded
in
the
ferromagnetic
amorphous
matrix, which act as pinning
centres
H (kA/m)
-0.08
0
5
10
H (kOe)
CRITICAL SIZE FOR PINNING
PROCESS IS RELATED TO THE
DOMAIN WALL WIDTH (δ)
Condition: d > δ
Conclusions
• Magnetic properties similar to the one achieved in
materials conventionally exploited in applications
• preparation
geometries;
in
one-step
process
in
different
• miniaturization opportunities for magnetic cores or
inductive components and could be used successfully
in making transformers, dc-dc and dc-ac converters,
magnetic heads, etc.
• have more degrees of freedom to tailor magnetic
properties due to the flexibility in composition, shape,
and dimensions.
Heat flow
EXO
DSC: as-prepared
•Significant
amount
of
an
amorphous phase is formed in
both samples regardless of the
quenching rate: strong exothermic
signal (around 500 °C) due to a
crystallisation process (see Fig. 1)
100 mW/g
AM master alloy
Tx = 531°C
CM Cone
300
350
Tx = 500°C
400
450
500
Temperature [°C]
550
•An additional exothermic signal is
observed at lower temperature
⇒ growth of Nd precipitates?
DSC traces of the Nd70Fe20Al10 as cast samples.
AM samples: master alloy ingots, through arc melting
CM samples: cone-shaped ingots (diameter from 1 to 4 mm ), by
copper mould casting
Effect of annealing
H e a t in g r a t e : 4 0 K / m in
150
EXO
A ) C o p p e r M o u ld C o n e
a s q u e n c h e d s a m p le
s a m p le p r e t r e a t e d u p t o 4 9 0 ° C
100
Heat flux (mW/g)
50
Heat treatments: performed in the DSC
cell at temperatures increasing from 200
to 500 °C (heating rate 40 K/min) with
each step of 50°C.
0
Tx = 461°C
150
B ) A r c m e lt e ld M a s t e r a llo y
a s c a s t s a m p le
100
s a m p le p r e t r e a t e d
1) as-quenched: subjected to a DSC
run up to (Tx-10)°C and then allowed
to cool to room temperature.
u p to 5 2 0 °C
2) the same specimen was heated
again up to 580°C to complete
crystallisation.
50
0
Tx = 491°C
250
300
350
400
450
500
550
T e m p e ra t u re (° C )
Dashed line: first DSC run stopped at (Tx-10)°C; Continuous line
second DSC run up to 580°C.
Magnetic behaviour : effect of annealing
300
• A reduction of Hc is observed in both samples,
especially in the AM master alloy (relative decrease
≈ 24%).
Hc (kA/m)
250
200
150
• An increase of magnetisation particularly evident in
the CM sample is observed. This effect can be
related to variation in composition of the residual
amorphous matrix induced by the thermal
treatments and resulting from the segregation of
Nd atoms in nanocrystalline form.
form
AM master alloy
CM sample
100
13,0
12,0
AM master alloy
CM sample
11,5
0,110
0,105
0,100
11,0
0,095
10,5
0,090
10,0
J (T)
M (emu/g)
12,5
• Hc reduction ⇒ size increase of the Nd
precipitates responsible for the pinning mechanism
of the domain walls and segregated from the matrix
during the alloy solidification.
Optimal dimensions of a nonnon-magnetic precipitate
to obtain maximum hardening effect ≈ domain wall
width [3]. A further increase beyond this size will
cause a decrease in the pinning effect.
0,085
9,5
0 50 100 150 200 250 300 350 400 450 500
Annealing temperature (°C)
Annealing treatment induces a growth of the
pre-existing Nd nanocrystals and a reduction
of their effectiveness as pinning centres, being
their size already above the optimal one.
Room-Temperature magnetic behaviour
H (kOe)
0
5
B)
10
0,10
AM master alloy
CM sample
pure Nd
5
0,05
0
0,00
-5
-0,05
-500
0
H (kA/m)
500
-0,10
1000
0
5000
10000
0,10
AM master alloy
CM sample
0,05
5
0,00
0
-5
-10
-10
-1000
-10000 -5000
10
M (emu/g)
M (emu/g)
10
-5
-1000
J (T)
-10
J (T)
A)
H (Oe)
-0,05
Annealing temperature = 350 °C
-500
0
500
-0,10
1000
H (kA/m)
Hc increases with the decrease of quenching rate
• No saturation at Hmax ⇒ hysteresis loop can be
decomposed into 2 terms: a) ferromagnetic contribution due
to the amorphous phase and b) paramagnetic contribution
due to the precipitated Nd.
•
Production techniques:
ARC MELTING
• 99.9% pure elements
• Water-cooled copper
plate
• Ar atmosphere
COPPER MOULDING
• Crushed portion of
master alloy
• melted in a quartz
tube
• ejected in a conical
copper mould
• Ar atmosphere
Nd70Fe20Al10
Planar Flow Casting
Ferromagnetic BMG
• The optimization of soft or hard magnetic properties (e.g.
by increasing the Fe content for increasing the saturation
magnetization) also affects the mechanical properties of
the material
• the use of such glasses as magnetic parts in various
devices is strongly related to their elastic and/or plastic
response.
• For practical use, it is desirable to exactly evaluate both
the magnetic and the mechanical behavior, the
modifications induced by (nano)crystalline inclusions, in
order to finally reach a suitable compromise between
magnetic and mechanical properties.
• Mechanical properties of ferromagnetic BMGs and
nanocomposites preliminarily investigated: fracture
strength ≥ 3 GPa and the Young’s modulus moduli of up
to 268 GPa n attained
materials very attractive for applications.
Soft Magnetic materials
Magnetic behaviour/ RS ribbons
•Faint coercivity: 4 kA/m
•high initial susceptibility
•No saturation
H [kA/m]
[kA/m]
H
-1500 -1000
-1000
-500
-500
00
500
500
10001000 1500
0.06
0.06
RS ribbon
ribbon 11
RS
RS ribbon
ribbon 22
RS
0.04
0.04
M [emu/g]
44
22
0.02
0.02
Langevin fit function of
RS 1 anhysteretic curve
00
0.00
0.00
-2
-2
-0.02
-0.02
Langevin fit function of
-4
-4
RS 2 anhysteretic curve
00




-0.04
-0.04
30% µ1 ~ 1·10-16 emu
-0.06
-0.06
70% µ2 ~ 5·10-18 emu
-6
-6
-15000
-10000
-20000
-15000
-10000 -5000
-5000
 µ ⋅H
M ∝ L
 kB ⋅T
J [T]
66
5000 10000
1000015000
15000
5000
20000
H [Oe]
[Oe]
H
SUPERPARAMAGNET:
•A collection of non-interacting magnetic
moments disordered by thermal energy
•Described by the Langevin Function (L)
Amorphous hard magnets ?
Hard magnetic behaviour in the as-cast
state for bulk amorphous samples;
Hard magnetic behaviour for partially
amorphous ribbons obtained at low speeds;
Soft magnetic behaviour for fully
amorphous ribbons spun at high speeds;
Paramagnetic behaviour after heat
treatment up to complete crystallisation
STRONG DEPENDENCE OF COERCIVE
FIELD ON QUENCHING CONDITIONS
Soft Magnetic materials
Efficient flux multiplier in a large variety of devices, including
transformers, generators, motors, to be used in the generation
and distribution of electrical energy, and a wide array of
apparatus, from household appliances to scientific equipment.
High initial magnetic permeability and/or maximum
• magnetic fast switching
• electronics
• magnetic recording and sensors
• magnetic shielding