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J. Magn. Soc. Jpn., 41, 63-65 (2017)

LetterTemperature Characteristics of the Dynamic Magnetic Loss of Ferrite
H. Saotome, K. Azuma and Y. Hamamoto

Faculty of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, JapanThe dynamic magnetic loss in ferrites is obtained by subtracting the hysteresis loss, which is independent of theexcitation frequency, from the iron loss. In the high frequency excitation region, the dynamic magnetic loss is thedominant component of the iron loss in ferrites. The iron loss in ferrite is temperature-dependent and thisdependence has been described in product catalogs, where the hysteresis and dynamic losses are not separated. The
catalog data are measured using sinusoidal wave voltage excitation, whereas ferrite cores are commonly used underrectangular wave voltage excitation in DC-DC converters. In this paper, the experimentally obtained temperature
characteristics of the hysteresis and dynamic magnetic losses for rectangular wave voltage excitation are shown
separately, and it is found that the two are different. This suggests that the physical mechanisms involved aredifferent as well. Thus, it is important to consider the temperature characteristics of the dynamic magnetic loss toproduce low-loss ferrites.
Key words: ferrite, Mn-Zn, iron loss, dynamic magnetic loss, B-H loop, temperature
1. Introduction
Ferrite cores are mainly used in DC-DC converters,
where their switching frequencies are typically around
100 kHz. The eddy current loss in ferrites is negligible,
even when they are excited at such high frequencies,
because of the very high resistivity of grain boundaries.
Thus, the power loss of ferrites is considered to be themagnetic loss. For a given magnetic induction
maximum, Bm, the power loss of ferrites depends on thetemperature. This dependence has been described in a
product catalog, where the excitation voltage waveform
used was sinusoidal 1).
The magnetic loss in ferrites consists of hysteresisand dynamic magnetic losses 2). The area of the B-H loop
varies with the exciting frequency, i.e., the time
derivative of the magnetic induction, dB/dt. Thehysteresis loss (J/m3) is defined as the minimum B-Hloop area with respect to the exciting frequency when Bm
is kept constant, as shown by the broken line in Fig. 1.
When the excitation frequency, or dB/dt, is increased,
the B-H loop widens, as depicted by the solid line in Fig.
1. The dynamic magnetic loss (J/m3) is defined by thegray area in the figure.
Although it is of great interest to investigate thegeneration mechanism of the magnetic losses, this isnot easy. To determine whether the hysteresis anddynamic magnetic losses are generated by the same
BOFig. 1

B-H loop.

HFig. 2

Toroidal core used in experiments.

mechanism, the present authors measured thetemperature behavior of both quantities in a previous
study 3). We found no significant difference of thedynamic magnetic loss between at 0 °C and at room
temperature. In that study 3), we used TDK PC40
Mn-Zn ferrite, whereas here, we used TDK PC47, whose
power loss temperature dependence is approximately
1.8 times stronger than that of PC40 1). The dimensionsof the core used in the experiments is shown in Fig. 2.
The power loss measurements were carried out at 0 °C
and 30 – 70 °C.
2. Instrumentation
In order to set the temperature of the ferrite core to0 °C and 30 – 70 °C, the temperature control setups
shown in Figs. 3(a) and 3(b), respectively, wereprepared. The core was completely submerged in
distilled water in both cases. In Figs. 3(a) and 3(b), thedistilled water was surrounded by ice and a thermal
insulator, respectively. In Fig. 3(b), the watertemperature was controlled with a power source, heater,and thermocouple. The duration of the excitation wasshort enough to keep the rise in core temperature below
1 °C.
The product catalog for PC47 shows the temperature
characteristics of the core loss under sinusoidal
waveform voltage excitation at 100 kHz and Bm = 200(mT). The measurement results obtained in the range of30 °C to 70 °C using the present setup coincide with theJournal of the Magnetics Society of Japan Vol.41, No.3, 201763

Shuntresistori1

Rectangular
waveform
voltage sourcev2

Rs ls

Ferrite corevsDistilled waterIce(a) At roughly 0 °C
Shunt
resistorRectangularwaveform
voltage source

v2i1

Rs lsvs(a) 0 °C

PID-controlled
power source

Ferrite core

Distilled water

Thermocouple

Heater

Thermal insulator(b) Above 30 °C
Measurement setups.

3. Measurement results
Six B-H loops measured at 0 °C and 70 °C are shownin Figs. 4(a) and 4(b), respectively. They were obtained
under rectangular waveform voltage excitation withdB/dt = 1, 200, 400, 600, 800 and 1000 mT/s. The
smallest and largest B-H loops in the figures correspondto 1 and 1000 mT/s, respectively. The maximum
magnetic flux density, Bm, was kept at 200 mT for each B-Hloop. Between 0 °C and 70 °C, the power loss of theferrite decreases with increasing temperature. Thehysteresis loss corresponding to the area of the smallest
B-H loop in each figure also decreases. Moreover, the64(b) 70 °C
Fig. 4B-H loops (Bm = 200 mT).

1210Loss (J/m3)

catalog data under the same conditions.
In this study, the ferrite core was excited by arectangular waveform voltage, i.e., at constant dB/dt,
because we wanted to measure the power loss of theferrite with respect to the parameter dB/dt. The
rectangular waveform voltage sources shown in Figs.
3(a) and 3(b) consisted of a function generator and an
amplifier, or an FET inverter. The amplifier and FET
inverter were used to generate dB/dt smaller and larger
than 200 mT/s, respectively.
To measure the excitation current, i1, a shunt
resistor with a known stray inductance was used. The i1
waveform was calculated by using the shunt resistor
voltage, vs, and the compensation for the deviation due
to the stray inductance. B-H loops are obtained with i1,
the time integral of the search-coil-induced voltage, v2,
and the core dimensions. When the excitation current istoo large, v2 deviates from the rectangular waveform
due to vs. In such cases, the output waveform of thefunction generator is adjusted to compensate for thedistortion 3).

864200102030
4050
Temperature (℃)

6070304050
Temperature (℃)

6070(a) Bm = 100 mT
2520Loss (J/m3)

Fig. 315105001020(b) Bm = 200 mT

Fig. 5 Temperature characteristics of the dynamic
magnetic loss with dB/dt = 1000, 800, 600, 400 and 200
mT/s from the top down, respectively. The bottom
broken lines show the hysteresis losses.

Journal of the Magnetics Society of Japan Vol.41, No.3, 2017

(a) Bm = 100 mT

the hysteresis losses. The dynamic magnetic loss
becomes larger than the hysteresis loss and dominateswith increasing dB/dt, regardless of the temperature. To
investigate whether the difference in temperature
characteristics between the hysteresis and dynamic
magnetic losses can be clarified, the normalized values
were re-plotted (see Fig. 6), with 100 % representing thevalues at 0 °C for each of the losses. Figures 6(a) and6(b) revealed that between 0 °C and 30 °C, thehysteresis loss decreased with temperature more
steeply than the dynamic magnetic loss; the normalized
hysteresis loss curves in Figs. 6(a) and 6(b) almost
coincide. Thus, the temperature characteristics of thehysteresis and dynamic magnetic losses are different,
which suggests that, microscopically, their generation
mechanisms are not precisely the same.
4. Conclusions(b) Bm = 200 mT
Fig. 6 Temperature characteristics of the dynamic
magnetic loss: normalized values with respect tothe values at 0 °C for dB/dt = 1000 (●) and 200 (○)
mT/s. The bottom broken lines show the hysteresis
losses normalized to the values at 0 °C.
dynamic magnetic loss decreases slightly. In Fig. 4, themagnetic field intensities fluctuate a little near ±Bm,i.e., the exciting current oscillates slightly when therectangular waveform voltage changes its polarity very
quickly. The fluctuation is caused by the stray
capacitance of the winding. However, it does not
influence the B-H loop areas, because the energy stored
in the stray capacitance does not affect the area in aperiod. The capacitance energy is restored to the voltage
source.
Similar to the experiments resulting in Fig. 4, B-H
loops were also measured at 30, 40, 50, 60 and 70 °C. The
temperature characteristics of the hysteresis anddynamic magnetic losses are shown in Figs. 5(a) and5(b), where Bm is kept at 100 mT and 200 mT, respectively.
The measured dynamic magnetic losses are plotted withdB/dt = 1000, 800, 600, 400 and 200 mT/s from the top down,
respectively, and the bottommost broken lines represent

The hypothesis that the dynamic magnetic loss
corresponds to the eddy current loss in ferrite grains
has been disproved 4). Thus, the dynamic magnetic loss
must be caused by a magnetic phenomenon explainable
by electron spins, as in the case of the hysteresis loss,
whereas the eddy current can be explained by freeelectron motion. However, the experimental resultspresented here suggest that the generation mechanismof the dynamic magnetic loss cannot be exactly thesame as that of the hysteresis loss, given the differencein their temperature characteristics.
The hysteresis losses, normalized to the values at
0 °C, decrease with temperature to a greater extent
than the normalized dynamic losses. On the other hand,
the temperature dependence of the dynamic magnetic
loss in the raw data is stronger than that of thehysteresis loss. The dynamic magnetic loss is more
dominant under large dB/dt conditions. Thus, ferrite
manufacturers need to observe closely the temperature
characteristics of the dynamic magnetic loss, rather
than evaluating only the total magnetic loss.
References
1) http://product.tdk.com/ja/catalog/datasheets/ferrite_mn-zn_

material_characteristics_ja.pdf

2) H. Saotome and Y. Sakaki: IEEE Trans. Magn., 33, 728(1997)
3) H. Saotome and H. Ohta: J. Magn. Soc. Jpn. 39, 62(2015)4) H. Saotome: J. Magn. Soc. Jpn. 40, 19(2016)
Received Feb. 15, 2017; Accepted Mar. 27, 2017

Journal of the Magnetics Society of Japan Vol.41, No.3, 201765