Simulations as a tool for visualization of the phenomenon Magnetic
hysteresis
N. Nancheva, A. Aleksandrova
University of Rousse
Introduction
Experiments based on computer simulations have already found widespread use as a
supplementary material in the teaching process. The simulation exercises sufficiently
complement traditional method of education and follow the present trends of cheap education
(especially expensive laboratory education) provide to obtain measured data alike as in
classical laboratory. Visualization of physics phenomena through such techniques as
demonstrations, simulations, models, video clips and movies can contribute to students`
understanding of physics concepts by attaching mental images to these concepts [1]. The use
of virtual instrumentation and related Computer Based Learning techniques produce a reduced
workload for teaching staff, a more user friendly interactive environment to study in and
allow students to study remotely if desired. With the use of visual aids within the laboratory,
such as Virtual Instrument, animations and narration students can not only gain a better
understanding of what they are doing but why they are doing it [2, 3].
The major advantage of computer simulations is an excellent visualization effect [2-4] that is
of special interest in the description of phenomenon “Magnetic hysteresis” since the effects of
magnetic field on ferromagnetic materials through action of abstract field is hard to imagine.
In this paper we present the development of a novel concept of teaching, allowing students to
explore theoretical and experimental aspects of act of magnetic field on ferromagnetic
material through simulation. Focussing on the essentials, it is particularly suited for increasing
students` insight into the physics of magnetic hysteresis. For engineering students this
phenomenon is of big interest according its practical applications. The magnetic memory
aspects of iron and chromium oxides make them useful in audiotape recording and for the
magnetic storage of data on computer disks.
A brief introduction into the physics of magnetic hysteresis
One of the most typical characteristic of ferromagnetic materials is magnetic hysteresis that is
due to a long-range ordering phenomenon at the atomic level which causes the unpaired
electron spins to line up parallel with each other in a region called a domain. The long range
order which creates magnetic domains in ferromagnetic materials arises from a quantum
mechanical interaction at the atomic level. This interaction is remarkable in that it locks the
magnetic moments of neighboring atoms into a rigid parallel order over a large number of
atoms in spite of the thermal agitation which tends to randomize any atomic-level order [5].
Within the domain, the magnetic field is intense, but in a bulk sample the material will usually
be unmagnetized because the many domains will themselves be randomly oriented with
respect to one another. Ferromagnetism manifests itself in the fact that a small externally
imposed magnetic field can cause the magnetic domains to line up with each other and the
material is said to be magnetized. Ferromagnets will tend to stay magnetized to some extent
after being subjected to an external magnetic field. This tendency to "remember their
magnetic history" is called hysteresis. The fraction of the saturation magnetization which is
retained when the driving field is removed is called the remanence of the material, and is an
important factor in permanent magnets. When a ferromagnetic material is magnetized in one
direction, it will not relax back to zero magnetization when the imposed magnetizing field is
removed. It must be driven back to zero by a field in the opposite direction. If an alternating
magnetic field is applied to the material, its magnetization will trace out a loop called a
hysteresis loop. Once the magnetic domains are reoriented, it takes some energy to turn them
back again.
Magnetic hysteresis in simulation laboratory experiment
Every simulation is to a certain extent only a simplified model of the real experiment. Core of
presented simulation laboratory exercise “Magnetic hysteresis” is Java applet [6]. For creation
of simulation experiment Web based technology has been used. Web pages were created by
Microsoft FrontPage, ArcSoft Photostudio 5.5 and Microsoft Photo Editor. Because most
standard applets are written with English controls and instructions, students with limited
knowledge of the English language might have problems understanding the basic concepts
governing the applet behaviour. For our purpose some of the text in the applet has been
translated in Bulgarian. The experiment has been created for students from engineering
courses of University of Rousse and can be used for distant learning or in addition of real
laboratory experiment. This simulation experiment has analog in real laboratory experiments
in University of Rousse, but in real experiment it is impossible to receive notion for domains
and their behaviour.
The simulation laboratory experiment “Magnetic hysteresis” contains typical parts or pages:

An introduction theoretical part informing the student about the physical phenomena,
which is demonstrated in simulation lab exercise (Fig.1).
Fig.1. “Magnetic hysteresis”
– theoretical part “

A part where the students may be prompted for the answers to three questions (entry
test). The student can only proceed with the exercise after giving the correct answers
(Fig.2).
 A part giving the practical instructions describing how to carry out the actual activities
and measurements of the lab exercise.
 Detailed measuring process description, the applet used in simulation and measuring
process (Fig.3).
 A part giving an overview of the results of the exercise allowing the student to print
these results. It is based on these data that the student will prepare a lab report.
Theoretical introduction and analysis of physical phenomenon is a very important part. When
student do not know the theory of physical phenomenon, shown in simulation experiment, it
will be only a computer game. Students must be very quickly introduced to the bases of
physical phenomenon, because they usually do not hold enough concentration and are not
patient when working at Internet.
Fig.2. “Magnetic hysteresis” –
entry test
Fig.3. “Magnetic hysteresis” – tasks, applet and results
The simulation lab exercise allows investigating the magnetization of ferromagnetic material
I at different intensities H of external magnetic field - I  f (H ) and different temperatures
- I  f (T ) . The laboratory exercise can be integrated in real laboratory experiment. It can
also be profitably used by the distant learners, who have often scarce or null opportunity to
access the laboratory in the university. Of course, when using simulation exercises, it is
important to bear in mind that the actual reality is inevitably more complicated than the virtual
one. Although the simulation exercises are very good as an educational addition, they could
not recompense the real classical lab experiments.
Video clips as a tool for visualization of magnetic hysteresis
Interactive video clips and movies are logical step in the progression of creating useful
visualizations for students. According to Kozma [7, 8] “the advantage of any video is in its
use of dynamic, visual symbolic systems that allow scientists to view any scientific
experiment or discovery from multiple or different perspectives”. In [9, 10] has been shown
that:
 The digital video activities and tools can be used by students to make connections
between concrete, real-life phenomena and the abstract ideas and models of physics.
 Students can create visual representations of their model and display it directly on the
video scene. In this way students can make direct visual comparisons between
complex events and simplified scientific models.
 Students can also combine images from different video frames and modify the
presentation of motion on the screen.
In the case of lab exercise “Magnetic hysteresis” we used movie [11] and video clip [12]
respectively, to visualize the phenomenon because the effect of magnetization is quantum
process and it is hard to explain and imagine. Students can compare behavior of the different
ferromagnetic materials; compare their hysteresis loops and connect it’s with their properties,
that there is important against to their practical applications (Figs. 4-6). Students can create
visual representations of different stages of magnetization, how is generating the hysteresis
loop and observe behavior of the magnetic domains (Fig. 7).
Fig.4.
Fig.5.
Fig.6.
Fig. 4, Fig. 5 and Fig.6 present three simulations at different values of the random field, which
determines the influence of disorder on the system [11]. The panel on the left displays the
lattice, spins are colored blue when down and colored green when up; clusters of spins flash
red when they flip. The panel on the right is a plot of magnetic field (horizontal) versus
magnetization (vertical.) The movie will run the model to the maximum and minimum
magnetic fields to generate a hysteresis loop; after that, it is possible to tell the movie to run
the model to a particular magnetic field by clicking on the control bar underneath the plot.
Fig.4. presents mostly small avalanches and narrow hysteresis loop that implies a small
amount of dissipated energy in repeatedly reversing the magnetization. Materials with narrow
hysteresis loop are desirable for transformer and motor cores to minimize the energy
dissipation with the alternating fields associated with AC electrical applications. Fig.5
demonstrates both very small and very large avalanches and saturation magnetization. The
area of the hysteresis loop is related to the amount of energy dissipation upon reversal of the
field. With the movie presented at Fig.6 students have possibility to observe very large
avalanches as most of the system changes magnetization as once. Materials with wide
hysteresis loop are desirable for permanent magnets and magnetic recording and memory
devices.
a – No external field
b – Week applied field
c – Strong applied field
d – Curve of initial
magnetization
Fig. 7.
Fig.7 shows frames from the visualization experiment [12] and presents different stages of
magnetization and behavior of domains (a – no external field; b – week applied field; c –
strong applied field; d – curve of initial magnetization). These illustrations of domains are
conceptual only and not meant to give an accurate scale of the size or shape of domains but
students get an idea about what happen in material. The microscopic evidence about
magnetization indicates that the net magnetization of ferromagnetic materials in response to
an external magnetic field may actually occur more by the growth of the domains parallel to
the applied field at the expense of other domains rather than the reorientation of the domains
themselves as implied in the sketch.
The sketches above suggest that the effect of external magnetic fields is to cause the domain
boundaries to shift in favour of those domains which are parallel to the applied field. It is not
clear how this applies to bulk magnetic materials which are polycrystalline. Keep in mind the
fact that the internal magnetic fields which come from the long range ordering of the electron
spins are much stronger, sometimes hundreds of times stronger, than the external magnetic
fields required to produce these changes in domain alignment. The effective multiplication of
the external field which can be achieved by the alignment of the domains is often expressed in
terms of the relative permeability.
Simulation may be used by the teacher to explain and demonstrate the phenomenon before the
student actually enters the real lab exercise.
Conclusions
The laboratory exercise presented in this paper can be used in addition of real laboratory
experiment. It can also be profitably used by the distant learners, who have often scarce or
null opportunity to access the laboratory in the university. Of course, when using simulation
exercises, it is important to bear in mind that the actual reality is inevitably more complicated
than the virtual one, so everybody should be invited to try, whenever possible, home made
experiments or to directly look at physical phenomena in nature. Although the simulation
exercises are very good as an educational addition they could not recompense the real
classical experiments.
Similar experiments allowing the student to compare the results of a numerical simulation in a
model and the behaviour in nature, and by that understanding how effectively a theory allows
the description of the physical reality.
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