Method of improving magnetic devices by applying AC or pulsed current

A method of improving the magnetic properties of a ferromagnetic materials is disclosed. The method comprises a step of providing a specimen made of Fe, Ni or Co based amorphous alloys in a magnetizing field and a second step of applying an AC current or pulsed current on the specimen to improve its soft magnetic properties. The applied AC current has a frequency of 50 to 50K Hz, a wave form of either sine wave, triangular wave or square wave, and a current density of 10 to 500 A/cm.sup.2. The magnetic properties of the ferromagnetic materials are improved by a coercivity ratio less than 0.5, a magnetic induction ratio greater than 1 and a core loss ratio less than 0.3.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for improving the magnetic 
properties of a magnetic material, and more particularly relates to a 
method for improving the magnetic properties of ferromagnetic amorphous 
alloys by applying AC current or pulsed current. 
Ferromagnetic amorphous alloys have been widely used in many magnetic 
applications such as distribution transformers, DC power supplies, motors, 
current amplifiers, magnetic shielding, etc. Fe-base amorphous alloys will 
produce an annealing embrittlement after the conventional furnace 
annealing. This is a serious problem in a certain applications. 
In the past, efforts have been made to find new magnetic materials suitable 
for many applications with better magnetic properties such as higher 
magnetic induction (Bm), lower coercivity (Hc), and therefore low core 
loss when the transformer core is made of such materials. For 
ferromagnetic materials used in the past for the manufacture of 
transformer cores, it is very difficult to change their magnetic 
properties in operation. 
SUMMARY OF THE INVENTION 
It is therefore the main object of the present invention to provide a 
method for improving the magnetic properties of the ferromagnetic 
amorphous alloys. 
An important feature of the present invention is the step of applying an AC 
current or pulsed current to the ferromagnetic amorphous alloys during the 
magnetization of the alloys to increase the maximum value of the magnetic 
induction (Bm) and decrease the minimum value of the coercivity (Hc). 
The AC current is originated from an AC power supply and fed into the 
specimen of the ferromagnetic materials by directly connecting to a pair 
of electrodes thereof. It is believed that the current passing the 
ferromagnetic material causes the domain wall in the material to shift in 
responsive to the current density and frequency. Therefore, the soft 
magnetic properties of the ferromagnetic materials are improved. The 
method of the present invention further comprises a step of applying an AC 
current or pulsed current to a specimen of alloy which has been treated by 
AC Joule heating or pulsed high current heating process. This amorphous 
alloy will not have annealing embrittlement during annealing process. The 
AC Joule heating or pulsed high current processes for improving the 
magnetic properties and annealing embrittlement of the alloy is invented 
by the same inventors of this subject invention and is detailed in 
co-pending application Ser. No. 338,895, now abandoned. 
The applied AC current or pulsed current has a frequency ranged from 50 to 
50K Hz, a current density of 10 to 500 A/cm.sup.2 and a wave form of sine 
wave, triangular wave or square wave. 
Accordingly, the method of improving the magnetic properties of 
ferromagnetic amorphous alloys of the present invention comprises a first 
step of providing a ferromagnetic amorphous alloy specimen in a 
magnetizing field, a second step of applying an AC current or pulsed 
current passing through said specimen, and a third step of detecting and 
recording the magnetic induction and coercivity of said specimen during 
magnetization and demagnetization process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The method for improving the magnetic properties of ferromagnetic amorphous 
alloys by applying high AC current or pulsed current is carried out and 
will become apparent in the following procedure. 
1. Specimens 
Ferromagnetic amorphous ribbons with different compositions, especially for 
Fe and Ni base amorphous ribbons. Also it is suitable for all crystalline 
material. 
Specimen shape -straight long ribbon 
toroid core wound by a long ribbon 
C-type, E-type or rectangular type core 
In our experiments, specimen of composition Fe.sub.78 B.sub.13 Si.sub.9 
were made into straight and toroidal shapes. 
2. Measuring the magnetic properties with AC current or pulsed current 
passing through the specimen 
A. Straight specimen 
The straight specimen was put in the center of a uniform magnetic field (H) 
produced by a long solenoid coil which was connected to a DC bipolar power 
supply of a function generator. Both ends of the straight amorphous ribbon 
were clamped by two square copper plates which were connected to the 
output terminals of an AC power supply which is capable of producing a 
search coil (S) combined with a compensating coil (C) was connected to a 
fluxmeter (or integrator) to measure the magnetic flux density (B) of the 
specimen. By connecting the terminals of the applied magnetic field (H) 
and magnetic flux density (B) to a X-Y recorder, the B-H hysteresis loop 
was obtained. (FIG. 1) 
B. Toroidal specimen 
The toroidal specimen was made by winding a long amorphous ribbon coated 
with insulation materials. The two ends of the long ribbon were connected 
to the output terminals of the AC power supply. The toroidal core was 
wound by two coils, the primary coil (N.sub.1) was connected to a DC 
bipolar power supply or a function generator to produce the applied 
magnetic field (H), a and the second coil (N.sub.2) was connected to a 
fluxmeter (or integrator) to measure the magnetic flux density (B). Then, 
by connecting the terminals of H and B to a X-Y recorder, the B-H 
hysteresis loop was obtained. (FIG. 2) 
3. Conditions of the applied AC current through the specimen. 
frequency range: 50 Hz.about.50KHz 
wave form: sine wave, triangular wave and square wave 
current density: J=10 A/cm.sup.2 .about.5.times.10.sup.2 A/cm.sup.2 
Transverse field induced by AC current or pulsed current. 
Except in the vicinity of the ribbon edges, the magnetic field produced by 
applying a current I through a rectangular specimen is essentially 
transverse and varies linearly with distance from the ribbon midplane. 
FIG. 3 shows the cross section of amorphous ribbon and its possible 
magnetic domain structure. 
4. Examples of improvement on the various kinds of ferromagnetic amorphous 
alloys resulted from the method of the invention by applying AC current 
passing through the specimen made of ferromagnetic materials. 
EXAMPLE 1 
Specimen: straight shape (15.24 cm.times.3.05 mm.times.25 .mu.m) 
Composition: Fe.sub.78 B.sub.13 Si.sub.9 
Reference magnetic properties of as-cast specimen: 
When applied magnetic field: Hm=.+-.0.296 Oe 
a. magnetic induction: Bm.sub.o =7.16 KG 
b. coercive force: Hc.sub.o =0.074 Oe 
Effects of magnetic properties under AC current passing through the 
specimen: 
A. Dependence of AC current density 
When a 60 Hz sine wave current passing through the specimen with different 
current density J=0.about.3.34.times.10.sup.2 A/cm.sup.2 (I=0.about.250 
mA), the variations of the magnetic induction and coercivity of the 
specimen are shown in FIG. 4. The magnetic inductions under different 
current densities are almost the same which is a little higher than the 
value of as-cast specimen. However, the coercivity of the specimen 
decreases significantly as the current density increases. The decrease is 
slower after the current density is higher than 1.5.times.10.sup.2 
A/cm.sup.2. When the current density is 3.34.times.10.sup.2 A/cm.sup.2, 
the coercivity will be lower than one half value of the as-cast specimen. 
B. Frequency dependence 
When the specimen was carrying the same AC current (current density 
J=1.6.times.10.sup.2 A/cm.sup.2) with different frequency (50 Hz.about.20 
KHz), the variations of magnetic induction and coercivity of the specimen 
are shown in the FIG. 5. Also, the magnetic inductions are almost the same 
and a little higher than the value of as-cast specimen. The values of 
coercivity ratio are around 0.5 and the minimum values of coercivity are 
between the frequency range 100 Hz.about.1 KHz. 
C. Wave form dependence 
The wave form used in the AC current passing through the specimen may be 
sine wave, triangular wave and square wave. Under the same peak-peak 
current, the effect of improving the magnetic properties by square wave is 
the best, and the effects by sine wave and by triangular wave are almost 
the same. For 300 Hz current passing through the specimen, the variations 
of magnetic induction and coercivity when applied magnetic field is 
Hm=.+-.0.296 Oe are list as follows: 
______________________________________ 
wave form current(mA) Bm(KG) Hc(Oe) 
______________________________________ 
0 7.16 0.074 
sine 200 7.72 0.044 
triangle 200 7.72 0.044 
square 200 7.72 0.044 
sine 250 7.86 0.029 
triangle 250 7.86 0.029 
square 250 7.86 0.026 
______________________________________ 
EXAMPLE 2 
Specimen: toroidal specimen 
Composition: Fe.sub.78 B.sub.13 Si.sub.9 
A 5-layer amorphous core with diameter 3.8 cm was wound by a 60 cm long 
ribbon (width 7.5 cm, thickness 25 .mu.m, and weight 6.623 g) 
Reference magnetic properties of as-cast specimen: 
When applied magnetic field in measuring B-H loop is Hm=.+-.0.15 Oe 
a. magnetic induction Bm=6.71 KG 
b. coercivity Hc.sub.o =0.073 Oe 
Applying 60 Hz sine wave through the core, the improved magnetic induction 
and coercivity of the specimen are list follows: 
______________________________________ 
Current density J(A/cm.sup.2) 
Bm(KG) Hc(Oe) 
______________________________________ 
0 6.71 0.073 
2 .times. 10.sup.2 6.80 0.039 
5 .times. 10.sup.2 6.88 0.030 
______________________________________ 
EXAMPLE 3 
Specimen: straight shape (15 cm.times.3.05 mm.times.25 .mu.m) 
Composition: Fe.sub.78 B.sub.13 Si.sub.9 
A. As-cast specimen 
When applied magnetic field in measuring B-H loop is Hm=.+-.0.292 Oe 
magnetic induction Bm=7.07 KG 
coercive force Hc=0.075 Oe 
B. After AC Joule heating 
Conditions of AC Joule heating: 
frequency f=60 Hz 
current density J=3.0.times.10.sup.3 A/cm.sup.2 
heating time t.sub.h =50 sec 
applied field Hp=100 Oe 
When applied magnetic field in measuring B-H loop is Hm=.+-.0.292 Oe 
magnetic induction Bm=9.70 KG 
coercivity Hc=0.04 Oe 
And, fracture strain .epsilon..sub.f =1 (ductility) 
C. Passing AC current through the specimen after AC Joule heating 
Conditions of AC current 
frequency: f=300 Hz 
wave form: square 
current density: 1.6.times.10.sup.2 A/cm.sup.2 
When applied magnetic field in measuring B-H loop is Hm=.+-.0.292 Oe 
magnetic induction Bm=9.89 KG 
coercivity Hc=0.017 Oe 
The dc B-H loops of the specimen as-cast, after AC Joule heating and AC 
current passing through the specimen are shown in FIG. 6. 
Although the method of the present invention has been described by way of 
preferred embodiments, it is to be noted that changes are still possible 
for those skilled in the art without departing from the spirit of the 
invention.