William R. Wieserman

University of Pittsburgh, Johnstown, Johnstown, Pennsylvania

Gene E. Schwarze

Glenn Research Center, Cleveland, Ohio

Janis M. Niedra

QSS Group, Inc., Cleveland, Ohio

Magnetic and Electrical Characteristics

of Cobalt-Based Amorphous Materials

and Comparison to a Permalloy Type

Polycrystalline Material

NASA/TM—2005-213997

December 2005

AIAA–2005–5720

https://ntrs.nasa.gov/search.jsp?R=20060008695 2018-05-17T09:02:54+00:00Z
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William R. Wieserman

University of Pittsburgh, Johnstown, Johnstown, Pennsylvania

Gene E. Schwarze

Glenn Research Center, Cleveland, Ohio

Janis M. Niedra

QSS Group, Inc., Cleveland, Ohio

Magnetic and Electrical Characteristics

of Cobalt-Based Amorphous Materials

and Comparison to a Permalloy Type

Polycrystalline Material

NASA/TM—2005-213997

December 2005

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for the

Third International Energy Conversion Engineering Conference

sponsored by the American Institute of Aeronautics and Astronautics

San Francisco, California, August 15–18, 2005

AIAA–2005–5720
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Available electronically at http://gltrs.grc.nasa.gov
NASA/TM—2005-213997 1 

Magnetic and Electrical Characteristics of Cobalt-Based 

Amorphous Materials and Comparison to a Permalloy 

Type Polycrystalline Material 

William R. Wieserman 

University of Pittsburgh, Johnstown 

Johnstown, Pennsylvania 15904 

Gene E. Schwarze 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Janis M. Niedra 

QSS Group, Inc. 

Cleveland, Ohio 44135 

Magnetic component designers are always looking for improved soft magnetic core materials to increase the 

efficiency, temperature rating and power density of transformers, motors, generators and alternators, and energy 

density of inductors. In this paper, we report on the experimental investigation of commercially available cobaltbased amorphous alloys which, in their processing, were subjected to two different types of magnetic field anneals: 

A longitudinal magnetic field anneal or a transverse magnetic field anneal. The longitudinal field annealed material 

investigated was Metglas® 2714A. The electrical and magnetic characteristics of this material were investigated 

over the frequency range of 1 to 200 kHz and temperature range of 23 to 150 °C for both sine and square wave 

voltage excitation. The specific core loss was lower for the square than the sine wave voltage excitation for the same 

maximum flux density, frequency and temperature. The transverse magnetic field annealed core materials include 

Metglas® 2714AF and Vacuumschmelze 6025F. These two materials were experimentally characterized over the 

frequency range of 10 to 200 kHz for sine wave voltage excitation and 23 °C only. A comparison of the 2174A to 

2714AF found that 2714AF always had lower specific core loss than 2714A for any given magnetic flux density and 

frequency and the ratio of specific core loss of 2714A to 2714AF was dependent on both magnetic flux density and 

frequency. A comparison was also made of the 2714A, 2714AF, and 6025F materials to two different tape 

thicknesses of the polycrystalline Supermalloy material and the results show that 2714AF and 6025F have the 

lowest specific core loss at 100 kHz over the magnetic flux density range of 0.1 to 0.4 Tesla. 

Nomenclature 

I

2

R winding power losses measured in Watts 

B-H hysteresis plot of magnetic flux density B versus magnetic field intensity H

SCL specific core loss measured in Watts per pound, Watts per cubic meter, or Watts per cubic centimeter 

BM maximum magnetic flux density measured in Tesla 

f electrical frequency measured in Hertz 

ip(t) the primary excitation current measured in Amperes 

es(t) the secondary induced voltage measured in volts 

T the core temperature measured in Celsius 

I. Introduction 

 Almost all power electronic circuits, such as inverters and converters, require power magnetic components. 

These magnetic components function as either power transfer or energy storage devices, and in some cases fulfill 

both needs. Increasing the operating frequency of the power magnetic components will reduce their mass and size1

. 

Increasing their operating temperature will admit smaller cooling radiators or heat sinks and also reduce the 

complexity of the heat transport system. 
NASA/TM—2005-213997 2 

Magnetic components designers are always looking for improved soft ferromagnetic core materials to increase 

the efficiency, temperature rating and power density of transformers, motors, generators and alternators, and energy 

density of inductors. The primary means to increase the transformer’s efficiency is to decrease the loss in the 

magnetic core material and the I

2

R or Joulean loss in the windings. The primary means to increase the transformer’s 

power density is to increase the frequency. But increasing the frequency without a decrease in the magnetic flux 

density will increase the core loss. So in most instances, the trade-off between power density, efficiency, and 

temperature rise comes down to a trade between operating frequency and magnetic flux density of the magnetic core 

material and current density in the windings. It should be noted that increasing the frequency will also increase the 

AC I

2

R loss in the windings. 

A very essential element in the design of power magnetic components is the knowledge of the electrical and 

magnetic properties and characteristics of available soft magnetic core materials. Properties such as saturation 

induction, Curie temperature, and thermal conductivity can generally be obtained from the product literature 

provided by the manufactures and fabricators of soft magnetic materials. However, experimental characterization 

data such as the effect of temperature, frequency, flux density, lamination or tape thickness, and excitation 

waveform on the core loss and dynamic B-H hysteresis loop are not always readily available. In many instances 

neither the manufacturer’s product literature nor the technical literature provide the required information. This 

almost total lack of information is particularly true for non-sinusoidal excitation core loss data. In most power 

electronic circuits such as switched mode power supplies, the excitation voltage impressed on the converter’s 

transformer is non-sinusoidal, and in DC-DC converters such as the push-pull and bridge converters, voltage 

excitation waveform is a square wave. Because of this lack of non-sinusoidal excitation core loss data, the 

transformer designer for switched mode power supplies, must generally fall back to using core loss data obtained for 

sine wave voltage excitation, assuming that even this data exists. Because of this lack of design data, the NASA 

Glenn Research Center initiated an experimental program to investigate the electrical and magnetic characteristics of 

candidate soft magnetic materials for temperatures up to 300 °C and frequencies up to 1 MHz for both sine and 

square wave voltage excitations. 

The core loss, that is, the power loss, of soft magnetic materials is a function of the excitation frequency, 

magnetic flux density, temperature, type of excitation (voltage or current), excitation waveform (sine, square, etc.), 

and lamination or tape thickness. A summary of core loss theory is given in Reference 8. In previously published 

papers2,3,4,5,6,7,8 we have reported on the specific core loss, SCL, and dynamic B-H hysteresis loop behavior for 

several polycrystalline, nanocrystalline, and amorphous soft magnetic materials. In this previous research we 

investigated the effects of magnetic flux density, frequency, temperature, tape thickness, and excitation waveform 

for voltage excitation on the SCL and dynamic B-H hysteresis loops. The soft magnetic materials investigated 

included an 80Ni-Fe polycrystalline alloy2,3,6,8, two 50Ni-Fe polycrystalline alloys4

, a 2V-49Fe-49Co polycrystalline 

alloy5

, a grain oriented 3Si-Fe polycrystalline alloy5, two iron-based amorphous alloys3,4, two cobalt-based 

amorphous alloys7, and an iron-based nanocrystalline alloy7. 

The difference in core loss and B-H loop behavior resulting from either a sine or square wave voltage excitation 

was previously investigated by C.H. Chen9

, T. Sato and Y. Sakaki10, and G.E. Schwarze, W.R. Wieserman, and J.M. 

Niedra6

. Chen investigated several materials and depending on material and flux density, the test frequencies ranged 

between 10 and 100 kHz. Chen found for like conditions of maximum magnetic flux density, BM, and frequency, f, 

that the core loss was larger for sine wave than for square wave voltage excitation. Sato and Sakaki tested materials 

similar to those investigated by Chen, but extended the test frequency up to 1 MHz. Their results were similar to 

those reported by Chen. In these papers there is no indication that their tests were conducted for temperatures 

beyond 50 °C. Schwarze, Wieserman, and Niedra did extensive experimental tests on an 80Ni-Fe alloy known in the 

trade as Supermalloy. Their investigation covered the frequency range of 1 kHz to 50 kHz and temperature range of 

23 to 300 °C. An analytical investigation of the sine and square wave SCL always found that the sine wave SCL for 

the same BM, f, and T was always greater than the square wave SCL. It was also found that the ratio of sine-to-square 

SCL varied up to 22 percent6

 depending on BM, f, and T. 

In this paper, we will report on an experimental investigation of commercially available cobalt-based amorphous 

alloys which, in their processing, were subjected to two different types of magnetic anneals: a longitudinal or 

transverse magnetic field anneal. The longitudinal magnetic field anneal is applied parallel to the rolling direction 

and in the plane of the magnetic tape while the transverse magnetic field anneal is applied perpendicular to the 

rolling direction and in the plane of the tape. 

We previously investigated very thin tape Permalloy (80Ni-20Fe-4Mo) type polycrystalline material and found 

the 1⁄4-mil thick tape to have very low core loss. The Permalloy type materials are relatively “old” technology 

materials compared to the relatively “new” amorphous magnetic materials. The SCL for this 1⁄4-mil thick tape will be 

included in a comparison to several amorphous materials. 
NASA/TM—2005-213997 3 

In addition, dynamic B-H loops for the materials investigated in this paper will be presented to show the effects 

of frequency and excitation waveform on the size and shape of these loops. 

II. Materials and Test Core Description 

The amorphous longitudinal magnetic field annealed Metglas® 2714A test cores were wound by Magnetics, a 

Division of Spang and Company, in the form of a toroid with nominal tape thickness of 20 μm. The width of the 

tape was 0.25 inch and nominal core dimensions were OD = 1.25 inches and ID = 1.0 inch. The amorphous 

transverse magnetic field annealed Metglas® 2714AF, also known as MAGNAPERM®, test core was provided to 

NASA Glenn Research Center as a sample toroid core by Allied Signal, Inc., Parsippany, NY. The tape thickness of 

the toroid was also a nominal 20 μm with core dimensions of OD = 1.75 inches, ID = 0.875 inches and height = 

0.375 inches. 

The manufacturer’s literature11 for the 2714A and 2714AF gives a saturation flux density of 0.57 T, saturation 

magnetostriction of less than 1 ppm, Curie temperature of 225C, crystallization temperature of 550 °C, continuous 

operating temperature of 90 °C, and mass density of 7.59 gm/cm3. The composition of 2714A and 2714AF 

according to the manufacturer’s Material Safety Data Sheet12 in weight percent is Cobalt (75 – 90), Iron (7 - 13), 

Nickel (1 – 5), Silicon (7 – 13), and Boron (1 – 5). 

III. Experimental Description 

The measurement system used to measure, compute, plot, and display the electrical and magnetic characteristics 

of the test core material is shown in Figure 1. A key element of the measurement system is the power amplifier used 

to excite the core material. The introduction of amplitude or phase distortion by the amplifier, and this is particularly 

true for square wave voltage excitation, will produce erroneous core loss and B-H dynamic loops. The method used 

to obtain the SCL and B-H dynamic loops from the primary excitation current, ip(t), and the secondary induced 

voltage, es(t), waveforms is described and discussed in Reference 2. 

The electrical and magnetic characteristics of the 2714A material were tested over the frequency range of 1 to 

200 kHz and temperature range of 23 to 150 °C for both sine and square wave voltage excitation. The electrical and 

magnetic characteristics of the 2714AF material were tested over the frequency range of 10 to 100 kHz for sine 

wave voltage excitation and 23 °C only. BM was either the saturation flux density for the low frequencies or that BM

for which the SCL remained less than 100 W/lb. Particular attention was given to capturing the required waveforms 

in the minimum length of time. 

IV. Experimental Results and Discussion 

Effects of the BM, f, and T on the SCL can best be seen and analyzed for trends by plotting the data as follows: 

1. SCL versus BM with f as the parameter for a given T. 

2. SCL versus f with BM as parameter for a given T.

3. SCL versus T with f as parameter for a given BM.

The effects of a longitudinal magnetic field anneal (2714A) and transverse magnetic field anneal (2714AF) on 

the SCL can best be seen and analyzed for trends by plotting the data as follows: 

1. Ratio of 2714A to 2714AF SCL versus BM with f as the parameter. 

2. Ratio of 2714A to 2714AF SCL versus f with BM as the parameter. 

A. Longitudinal Magnetic Field Anneal (2714A) 

The effects of BM and f on the SCL at a temperature of 23 °C for sine and square wave voltage excitation are 

shown in the Figure 2 and 3 plots, respectively for the 2714A material. 

The curve for a given f shows that the SCL tends to increase nearly linearly with increasing BM on a log-log scale 

for both the sine wave excitation (Figure 2a) and the square wave excitation (Figure 2b). Likewise, the plots for a 

given BM shows that the SCL tends to increase nearly linearly on a log-log scale with f for both sine wave excitation 

(Figure 3a) and square wave excitation (Figure 3b). A comparison of either Figure 2a (sine wave excitation) to 

Figure 2b (square wave excitation) or Figure 3a (sine wave excitation) to Figure 3b (square wave excitation) shows 

that the SCL is larger for sine wave excitation than for square wave excitation. For example, at BM = 0.4 Tesla, the 

ratio of sine-to-square wave SCL varies from 1.03 at 1 kHz to 1.09 at 50 kHz. In general, this is the range of 

variation of the sine-to-square SCL ratio for the other BM values tested. This same comparison of sine-to-square 

wave SCL ratio was previously done for a 1-mil thick tape Supermalloy toroid at BM = 0.4 Tesla at 23 °C6

. In this 

case, the ratio varied between 1.17 and 1.22 over the frequency range of 1 to 50 kHz. This comparison readily shows 

that the sine-to-square wave SCL ratio is greater for the polycrystalline Supermalloy material than for the amorphous 
NASA/TM—2005-213997 4 

2714A material. The reason for this rather large difference in the ratios is not readily apparent and additional 

experimentation and analysis will be required to determine the underlying cause. However, these results would 

imply that the core loss mechanism for a polycrystalline magnetic material is different than that for an amorphous 

magnetic material when subjected to different types of excitation. 

Figure 4a (sine wave excitation) and Figure 4b (square wave excitation) plot the SCL as a function of 

temperature for BM = 0.4 Tesla with f as the parameter for the 2714A material. The “flatness” of the SCL versus T 

curves plotted in these figures is seen to be a function of frequency. For 5 and 10 kHz, the SCL curves tend to a 

slight minimum at 100 °C and then increase in slope from 100 to 150 °C, but the SCL value at 150 °C is less than 

that at 23 °C. For 20 and 50 kHz, the slope of the SCL curves decreases slightly from 23 to 100 °C and then the 

slope increases from 100 to 150 °C, but the SCL value at 150 °C is greater than that at 23 °C. The relative increase in

SCL at 150 °C is greater for 50 kHz than for 20 kHz compared to the SCL at 23 °C. For 100 kHz, the slope of the

SCL curve shows a steady increase over the temperature range of 23 to 150 °C. 

Figure 5a (sine wave excitation) and Figure 5b (square wave excitation) give a family of dynamic B-H loops for 

frequencies of 1, 5, 10, 20, and 100 kHz for BM = 0.4 Tesla and T = 23 °C for the 2714A material. A comparison of 

the B-H loops in Figure 5a with those in Figure 5b shows that the shape of the loop is excitation dependent. Sine 

wave voltage excitation gives rounded corners at ± BM while square wave voltage excitation gives pointed corners at 

± BM. Both sets of loops give a good visual image of how the size or area of the loop increases with frequency due 

to eddy current loss. Another observation is that the ac coercive force is less for the square wave than for the sine 

wave excitation for a given frequency. And finally, it should be noted that loops for both sine and square wave 

excitation are quite symmetrical about the origin. 2714A is a “square-loop” type of material for which the ratio of 

remanence to maximum flux density approaches unity. “Square loop” types of materials tend to “ratchet” towards 

either ± BM and thus give non-symmetrical loops. 

Figure 6 gives a good visual picture of a comparison of a 2714A B-H loop for sine and square wave voltage 

excitation at BM = 0.4 Tesla, f = 100 kHz, and T = 23 °C. It is readily seen that the square wave excitation B-H loop 

fits entirely within the area of the sine wave excitation B-H loop except for tip areas about ± BM. If these two tip 

areas are subtracted from the area of the sine wave excitation B-H loop, it is seen that the area (i.e., core loss) 

enclosed by the sine wave excitation B-H loop is larger than the area enclosed by the square wave excitation B-H 

loop. 

B. Transverse Magnetic Field Anneal (2714AF) 

The effects of BM and f on the SCL at 23 °C for sine wave voltage excitation for the transverse annealed 2714AF 

material are given in Figures 7 and 8. Just as was observed for the longitudinal annealed 2714A, the curve for any 

given f in Figure 7 shows that the SCL increases nearly linearly with increasing BM on a log-log scale. Likewise, for 

any given BM, Figure 8 shows that the SCL increases nearly linearly with f on a log-log scale. 

Our primary interest in 2714AF is to compare the SCL of the transverse annealed material with the longitudinal 

annealed 2714A material to determine what advantage 2714A has over 2714AF. Figure 9 gives a comparison of 

these two material’s SCL as a function of BM with f as the parameter at 23 °C; Figure 10 gives this comparison of

SCL as a function of f with BM as the parameter at 23 °C. Inspection of the SCL versus BM curves in Figure 10 shows 

that for any given BM, the SCL is lower for the 2714AF than for the 2714A material for any given frequency. 

Likewise, inspection of the SCL versus f curves in Figure 11 shows that for any given f, the SCL is lower for the 

2714AF than for the 2714A material for any given BM. 

The results in Figures 9 and 10 clearly show the SCL advantages of the transverse anneal compared to the 

longitudinal anneal for comparable BM and f. However, Figures 9 and 10 do not quickly show quantifiably how 

much better the SCL is for 2714AF than for 2714A. By plotting the SCL ratio of 2714A to 2714AF, the clear 

advantage of 2714AF is readily seen. Figure 11 is a plot of the SCL ratio of 2714A to 2714AF versus BM for three 

frequencies at 23 °C. Figure 12 is a plot of this same SCL ratio versus f for four BM values. The SCL curves in 

Figure 11 show that the SCL ratio decreases as BM increases with the lowest frequency giving the largest ratio. The 

curves in Figure 12 show that the SCL ratio decreases as f increases with the lowest BM giving the largest ratio. The 

results in the two figures show that the SCL advantage of 2714AF over 2714A is greatest at low BM and low f and 

that this advantage diminishes as either BM or f increases. For example, at 20 kHz and BM = 0.1 Tesla, the ratio is 5.4 

while for this same frequency and BM = 0.5 Tesla, the ratio now decreases to 1.9. At 100 kHz and BM = 0.1 Tesla the 

ratio is 2.8 while for this same frequency and for BM = 0.4 Tesla, the ratio drops to 1.4. Even though the SCL 

advantage diminishes with increasing BM or f, the fact remains that the transverse annealed 2714AF material always 

has lower losses than the longitudinal annealed 2714A material for the frequencies and flux densities tested. 

The 2714AF dynamic B-H loops for frequencies 20, 50, and 100 kHz at BM = 0.4 Tesla and 23 °C are drawn in 

Figure 13. When this family of loops is compared to the family of loops for 2714A in Figure 5(a), the following is 
NASA/TM—2005-213997 5 

observed: (a) The 2714A loops are more squared, i.e., have a higher remanence than the 2714AF loops, (b) the 

2714AF loops are skewed or tilted to the right relative to the 2714A loops, and (c) a 2714A loop has more enclosed 

area than a 2714AF loop for any given frequency. A more direct comparison of the 2714A and the 2714AF dynamic

B-H loops for 100 kHz, 0.4 Tesla is displayed in Figure 14. This figure quickly shows that the 2714AF loop is 

entirely enclosed in the 2714A loop except for the small areas about ± BM. Figure 14 gives both a good picture of 

the loss advantage of 2714AF over 2714A and also the tilt of the 2714AF loop relative to the 2714A loop. 

C. SCL Comparison of Different Materials 

Of special interest and of great help to the magnetic component designer are SCL plots comparing various 

candidate soft magnetic materials over a range of flux densities and frequencies. SCL plots of this type reduce design 

time as they enable the designer to judiciously select the best material for the given design frequency and flux 

density. 

Figure 15 gives a plot of the SCL versus BM at 100 kHz and 23 °C for four different materials which includes not 

only the 2714A and 2714AF materials reported in this paper, but also the transverse annealed amorphous 6025F 

material manufactured by Vacuumschmelze, and poly crystalline Supermalloy material. The SCL for Supermalloy is 

given for 1-mil and 1⁄4-mil thick tape. Also, the SCL for both sine and square wave voltage excitation are given for 

2714A. The curves in Figure 15 show that the SCL for the transverse annealed 2714AF and 6025F materials yield 

the lowest losses with the 6025F material giving slightly lower SCL at low flux densities and slightly higher SCL at 

the higher flux densities compared to the 2714AF material. This figure also shows that the SCL for the 

polycrystalline 1⁄4-mil Supermalloy is much better than the longitudinal annealed 2714A for low BM, but this 

advantage is almost eliminated as BM approaches 0.3 Tesla. 

Figure 16 gives a plot of the SCL versus f at BM = 0.1 Tesla and 23 °C for the same materials shown in Figure 15. 

Again it is seen from this figure that the transverse annealed 2714AF and 6025F give the lowest SCL, but 6025F 

shows slightly lower SCL compared to 2714AF. Of special interest to note is that the 1⁄4-mil Supermalloy has a lower

SCL over the entire frequency range compared to the longitudinal annealed amorphous 2714A. Also it is interesting 

to note that the 1-mil Supermalloy has lower SCL than the 2714A up to 20 kHz. 

V. Summary and Conclusion 

An experimental study was conducted to investigate the combined effects of temperature and sine or square 

wave voltage excitation on the SCL and dynamic B-H hysteresis loops of the longitudinal magnetic field annealed 

amorphous Metglas® 2714A material. For the same BM, f, and T, the SCL was always lower for the square than the 

sine wave voltage excitation. In comparing the polycrystalline Supermalloy to Metglas® 2714A, it was found that 

the ratio of sine-to-square wave SCL was greater for Supermalloy than for 2714A at BM = 0.4 Tesla and T = 23 °C. 

The underlying reason for this is not immediately apparent and needs to be explored if this difference is to be 

attributed solely to the classical eddy current loss component of the total core loss. The effect of temperature on the 

SCL of 21714A for both sine and square wave voltage excitation was found to be minimal from 23 to 100 °C for BM

= 0.4 Tesla, but with a noticeable increase in SCL from 100 to 150 °C with the increase being more pronounced with 

increasing frequency. 

An experimental study was also conducted to investigate the effect of a transverse magnetic field annealed 

material on the SCL. A comparison of the SCL of 2714A (longitudinal magnetic field anneal) with 2714AF 

(transverse magnetic field anneal) found that 2714AF always had a lower SCL than 2714A for any given BM and f. 

In particular, it was found that the SCL ratio of 2714A to 2714AF was dependent on BM and f and that the highest 

ratio occurred for the lowest BM and f for decreasing ratio with either increasing BM or f. 

Finally, a comparison of the 2714A and 2714AF materials was made to another transverse magnetic annealed 

amorphous material, 6025F, manufactured by Vacuumschmelze and two different tape thicknesses of the 

polycrystalline material, Supermalloy. From the magnetic component designer’s viewpoint, the best material to use 

from this comparison in terms of SCL is either 2714AF or 6025F which have comparable losses at 100 kHz from BM

= 0.1 to 0.4 Tesla. This comparison also shows that the 1⁄4-mil thick tape Supermalloy has a lower SCL than the 

longitudinal annealed 2714A over the entire frequency range and magnetic flux density range investigated. The 

comparison also shows that the SCL of the 1-mil thick tape Supermalloy is competitive with the 2714A at low BM

and f. 
NASA/TM—2005-213997 6 

POWER

AMPLIFIER

ARBITRARY

FUNCTION

GENEATOR

CH1 CH2 CH3

DATA

AQUISITION

SYSTEM

( ) S e t

( ) Pi t

Figure 1.—Specific loss and dynamic B-H hysteresis loop measurement system. 
NASA/TM—2005-213997 7 

0.1 0.2 0.3 0.4 0.5

Magnetic Flux Density (T)

0.1

1

10

100

Specific Co

re Loss (w/lb)

200 kHz

100 kHz

50 kHz

20 kHz

10 kHz

5 kHz

1 kHz

(a) 

0.1 0.2 0.3 0.4 0.5

Magnetic Flux Density (T)

0.1

1

10

100

Specific Co

re Loss (w/lb)

1 kHz

100 kHz

50 kHz

20 kHz

10 kHz

5 kHz

200 kHz

(b) 

Figure 2.—Metglas® 2714A specific core loss versus maximum flux density at 23 °C with frequency as parameter 

for nominal 20 μm thick tape toroid. (a) Sine wave voltage excitation, (b) Square wave voltage excitation. 
NASA/TM—2005-213997 8 

0.3 T

0.2 T

0.5 T

0.4 T

10 100 20 30 40 50 60 70 80 90 200

Frequency (kHz)

0.1

1

10

100

Specific Co

re Loss (w/lb)

0.1 T

(a) 

0.3 T

0.2 T

0.5 T

0.4 T

0.1 T

10 100 20 30 40 50 60 70 80 90 200

Frequency (kHz)

0.1

1

10

100

Specific Co

re Loss (w/lb)

(b) 

Figure 3.—Metglas® 2714A specific core loss versus frequency at 23 °C with maximum flux density as parameter 

for nominal 20 μm thick tape toroid. (a) Sine wave voltage excitation, (b) Square wave voltage excitation. 
NASA/TM—2005-213997 9 

50 kHz

20 kHz

10 kHz

5 kHz

1 kHz

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Temperature (C)

0.1

1

10

100

Specific Co

re Loss (w/lb)

100 kHz

(a) 

50 kHz

20 kHz

10 kHz

20 30 40 50 60 70 80 90 100 110 120 130 140 150

Temperature (C)

0.1

1

10

100

Specific Core Loss (w/lb)

100 kHz

5 kHz

1 kHz

(b) 

Figure 4.—Metglas® 2714A specific core loss versus temperature at BM = 0.4 Tesla with frequency as the parameter 

for a nominal 20 μm thick tape toroid. (a) Sine wave voltage excitation, (b) Square wave voltage excitation. 
NASA/TM—2005-213997 10 

B (T)

H (A/m)

-15 -10 -5 0 5 10 15

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

100 kHz

50 kHz

20 kHz

10 kHz

5 kHz

1 kHz

(a) 

B (T)

H (A/m)

-15 -10 -5 0 5 10 15

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

100 kHz

50 kHz

20 kHz

10 kHz

5 kHz

1 kHz

(b) 

Figure 5.—Metglas® 2714A family of dynamic B-H loops at 23 °C for various frequencies at BM = 0.4 Tesla for a 

nominal 20 μm thick tape toroid. (a) Sine wave voltage excitation, (b) Square wave voltage excitation. 
NASA/TM—2005-213997 11 

B (T)

H (A/m)

-15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

Sinewave Excitation

Squarewave Excitation

Figure 6.—Comparison of a nominal 20 μm thick tape toroid Metglas® 2714A dynamic B-H loops for sine and 

square wave voltage excitation at 23 °C, BM = 0.4 Tesla, and f = 100 kHz. 
NASA/TM—2005-213997 12 

0.10 0.20 0.30 0.40 0.50

Magnetic Flux Density (T)

0

1

10

100 Specific Co

re Loss (w/lb)

20 kHz

50 kHz

3

100 kHz

00 kHz

200 kHz

500 kHz

(a) 

Figure 7.—Metglas® 2714AF specific core loss versus maximum magnetic flux density at 23 °C with frequency as 

the parameter for sine wave voltage excitation for a nominal 20 μm thick tape toroid. 

10 100

20 30 40 50 60 70 80 90 200

Frequency (kHz)

0

1

10

100

Specific Co

re Loss (w/lb)

0.4 T

0.3 T

0.2 T

0.1 T

(b) 

Figure 8.—Metglas® 2714AF specific core loss versus frequency at 23 °C with maximum magnetic flux density as 

the parameter for a nominal 20 μm thick tape toroid. 
NASA/TM—2005-213997 13 

0.1 0.2 0.3 0.4 0.5

Magnetic Flux Density (T)

0.1

1

10

100

Specific Core Loss (w/lb)

20kHz

200kHz

100kHz

200kHz

100kHz

20kHz

2714A

2714AF

Figure 9.—Comparison of Metglas® 2714A to 2714AF specific core loss versus maximum magnetic flux density at 

23 °C with frequency as the parameter for sine wave voltage excitation for nominal 20 μm thick tape toroid. 

10 100 20 30 40 50 60 70 80 90 200

Frequency (kHz)

0.1

1

10

100

Specific Core Loss (w/lb)

0.3 T

0.1 T

0.1 T

0.3 T

2714A

2714AF

0.2 T

0.4 T

0.4 T

0.2 T

Figure 10.—Comparison of Metglas® 2714A to 2714AF specific core loss versus frequency at 23 °C with 

maximum flux density as the parameter for sine wave voltage excitation for nominal 20 μm thick tape toroid. 
NASA/TM—2005-213997 14 

0.1 0.2 0.3 0.4

Magnetic Flux Density (T)

1

2

3

4

5

6

Ratio (SCL 2714A / SCL 2714AF)

200 kHz

100 kHz

20 kHz

Figure 11.—Specific core loss ratio of Metglas® 2714A to 2714AF material versus maximum magnetic flux density 

at 23 °C for three frequencies for sine wave voltage excitation for nominal 20 μm thick tape toroids. 

20 40 60 80 100 120 140 160 180 200 30 50 70 90 110 130 150 170 190

Frequency (kHz)

1

2

3

4

5

6

Ratio (SCL2714A to SCL2714AF)

0.1 T

0.2 T

0.3 T

0.4 T

Figure 12.—Specific core loss ratio of Metglas® 2714A to 2714AF material versus frequency at 23 °C for four 

maximum magnetic flux densities for sine wave voltage excitation for nominal 20 μm thick tape toroids. 
NASA/TM—2005-213997 15 

B (T)

H (A/m)

-15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

 100 kHz

 50 kHz

 20 kHz

Figure 13.—Metglas® 2714AF family of dynamic B-H loops at 23 °C for various frequencies at 

BM = 0.4 Tesla for sine wave voltage excitation for a nominal 20 μm thick tape toroid. 

B (T)

H (A/m)

-15 -13 -11 -9 -7 -5 -3 -1 1 3 5 7 9 11 13 15

-0.5

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

2714A Sinewave Excitation

 2714AF Sinewave Excitation

Figure 14.—Comparison for nominal 20 μm thick tape toroids Metglas® 2714A to 2714AF dynamic B-H loops for 

sine wave voltage excitation at 23 °C, BM = 0.4 Tesla, and f = 100 kHz. 
NASA/TM—2005-213997 16 

0.1 0.2 0.3 0.4

Magnetic Flux Density (T)

1

10

100

Specific Core Loss (w/lb)

2714AF

1-mil Supermalloy

1/4-mil Supermalloy

2714A

6025F

2714A(Square wave)

Figure 15.—Comparison of the specific core loss versus maximum magnetic flux density of different magnetic 

materials for sine wave voltage excitation, except where noted, at 23 °C and 100 kHz. 

10 100 20 30 40 50 60 70 80 90 200

Frequency (kHz)

0.1

1

10

100

Specific Core Loss (w/lb)

1-mil Supermalloy

2714A

2714AF

1/4-mil Supermalloy

2714A (Square Wave)

6025F

Figure 16.—Comparison of the specific core loss versus frequency of different magnetic materials for sine wave 

voltage excitation, except where noted, at 23 °C and BM = 0.1 Tesla. 
NASA/TM—2005-213997 17 

References 

 

1

 Schwarze, G.E., “Development of High Frequency Low Weight Power Magnetics for Aerospace Power Systems”, Nineteenth 

Intersociety Energy Conversion Engineering Conference, San Francisco, CA, August 19-24, 1984. 2 Wieserman, W.R., Schwarze, G.E., and Niedra, J.M., “High Frequency, High Temperature Specific Core Loss and Dynamic BH Hysteresis Loop Characteristics of Soft Magnetic Alloys”, 25th Intersociety Energy Conversion Engineering Conference, Reno, 

Nevada, August 12-17, 1990. 

3 Wieserman, W. R., Schwarze, G. E., and Niedra, J. M, “Comparison of High Frequency, High Temperature Core Loss and B-H 

Loop Characteristics of an 80 Ni-Fe Crystalline Alloy and Two Iron-Based Amorphous Alloys,” Eighth Symposium on Space 

Nuclear Power Systems Proceedings, Part Three, Albuquerque, N.M., January 6-10, 1991. 4 Wieserman, W. R., Schwarze, G. E., and Niedra, J. M, “Comparison of High Temperature, High Frequency Core Loss and 

Dynamic B-H Loops of Two 50 Ni-Fe Crystalline Alloys and an Iron-Based Amorphous Alloy”, 26th Intersociety Energy 

Conversion Engineering Conference Proceedings, Boston, MA, August 4-9, 1991. 5 Wieserman, W. R., Schwarze, G. E., and Niedra, J. M, “Comparison of High Temperature, High Frequency Core Loss and 

Dynamic B-H Loops of a 2V-49Fe-49Co and a Grain Oriented 3Si-Fe Alloy”, 27th Intersociety Energy Conversion Engineering 

Conference, San Diego, CA, August 3-7, 1992. 6 Schwarze, G. E., Wieserman, W. R., and Niedra, J. M, “Effects of Temperature, Frequency, Flux Density and Excitation 

Waveform on the Core Loss and Dynamic B-H Loops of Supermalloy“, 30th Intersociety Energy Conversion Engineering 

Conference, Orlando, FL, July 31-August 4, 1995. 7 Niedra, J.M., Schwarze, G. E., “Wide Temperature Core Loss Characteristics of Transverse Magnetically Annealed Amorphous 

Tapes for High Frequency Aerospace Magnetics“, 34th Intersociety Energy Conversion Engineering Conference, Vancouver, 

British Columbia, Canada, August 1-5, 1999. 

8 Schwarze, G.E., Wieserman, W.R., and Niedra, J.M., “Magnetic and Electrical Characteristics of Permalloy Thin Tape Bobbin 

Cores”, 2nd International Energy Conversion Engineering Conference, Providence, Rhode Island, 16-19 Aug 2004. 9 Sato, T., and Sakaki, Y., “Discussion of Eddy Current Loss Under Square Wave Voltage Excitation”, IEEE Transactions on 

Magnetics, Vol. 24, No 6, November 1988, pp 2904-2906. 10 Chen, D.Y., “Comparison of High Frequency Magnetic Core Losses under Two Different Driving Conditions: A Sinusoidal 

Voltage and a Square Wave Voltage”, IEEE Power Electronics Specialist Conference, Record 1978, pp. 237-241. 11 Metglas® Technical Bulletin, www.metglas.com 12 Metglas® 2714A Cobalt Based Alloy, Material Safety Data Sheet, www.metglas.com
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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Available electronically at http://gltrs.grc.nasa.gov

December 2005

NASA TM—2005-213997

AIAA–2005–5720

E–15321

WBS–22–612–50–81–12

23

Magnetic and Electrical Characteristics of Cobalt-Based Amorphous Materials

and Comparison to a Permalloy Type Polycrystalline Material

William R. Wieserman, Gene E. Schwarze, and Janis M. Niedra

Specific core loss; B-H hysteresis loop; Magnetic field anneal; Sine wave voltage

excitation; Square wave; Voltage excitation; Permalloy; High frequency; Magnetic

measurements; Magnetic cores

Unclassified -Unlimited

Subject Category: 33

Prepared for the Third International Energy Conversion Engineering Conference sponsored by the American Institute of

Aeronautics and Astronautics, San Francisco, California, August 15–18, 2005. William R. Wieserman, University of

Pittsburgh, Johnstown, 450 Schoolhouse Road, Johnstown, Pennsylvania 15904; Gene E. Schwarze, NASA Glenn

Research Center; and Janis M. Niedra, QSS Group, Inc., 21000 Brookpark Road, Cleveland, Ohio 44135. Responsible

person, Gene E. Schwarze, organization code RPE, 216–433–6117.

Magnetic component designers are always looking for improved soft magnetic core materials to increase the efficiency, temperature

rating and power density of transformers, motors, generators and alternators, and energy density of inductors. In this paper, we report

on the experimental investigation of commercially available cobalt-based amorphous alloys which, in their processing, were subjected

to two different types of magnetic field anneals: A longitudinal magnetic field anneal or a transverse magnetic field anneal. The

longitudinal field annealed material investigated was Metglas® 2714A. The electrical and magnetic characteristics of this material

were investigated over the frequency range of 1 to 200 kHz and temperature range of 23 to 150 °C for both sine and square wave

voltage excitation. The specific core loss was lower for the square than the sine wave voltage excitation for the same maximum flux

density, frequency and temperature. The transverse magnetic field annealed core materials include Metglas® 2714AF and

Vacuumschmelze 6025F. These two materials were experimentally characterized over the frequency range of 10 to 200 kHz for sine

wave voltage excitation and 23 °C only. A comparison of the 2174A to 2714AF found that 2714AF always had lower specific core loss

than 2714A for any given magnetic flux density and frequency and the ratio of specific core loss of 2714A to 2714AF was dependent

on both magnetic flux density and frequency. A comparison was also made of the 2714A, 2714AF, and 6025F materials to two

different tape thicknesses of the polycrystalline Supermalloy material and the results show that 2714AF and 6025F have the lowest

specific core loss at 100 kHz over the magnetic flux density range of 0.1 to 0.4 Tesla.