Black and White Bloch

Black and White Bloch

The study of mainstream magnetism is firmly rooted in the era of “Black and White” movies.

This probably explains why the perennial classic “Magnetism – An Introductory Survey” by E. W. Lee is still available on Amazon 50 years after it was first published in 1963.

Magnetism - E W Lee

Unfortunately, the black and white movies from the 1950s and 60s are generally classed as low budget “B Movies” because the Technicolor motion picture process was invented in 1916.

Therefore, a Technicolor makeover of mainstream magnetism is long overdue.

Black and White Magnetism

The initial step in the makeover is to colourise the classic black and white “iron fillings” image to reveal any additional details that may be obscured in the original two tone image.

Changing the contiguous “white space” around the North Pole to “red space” and the contiguous “white space” around the South Pole to “blue space” reveals additional layers of information.

a) There is no contiguous “white space” that connects the North Pole to the South Pole.

b) The North Pole “white space” is marginally stronger than the South Pole “white space”.

c) A central demilitarised zone of “white space” is clearly observable [colour coded yellow].

Magnetic Field Lines - Colour Coded

Although the above exercise is not totally objective it does clearly illustrate that the original “black and white” imagery is visually misleading.

The sceptical reader [with the aid of a graphics package] should verify these results for themselves.

The intriguing central demilitarised zone of “white space” clearly depicts a transition zone where many of the black lines [iron fillings] clearly branch and terminate.

This is very suggestive of a Bloch Wall.

A Bloch wall is a narrow transition region at the boundary between magnetic domains, over which the magnetization changes from its value in one domain to that in the next, named after the physicist Felix Bloch.

Bloch domain walls appear in bulk materials, i.e. when sizes of magnetic material are considerably larger than domain wall width (according to the width definition of Lilley).

Investigating this central demilitarised zone can be very easily [and very cheaply] achieved by using a sewing needle and eight “button” magnets stacked together to form a cylinder magnet.

The presence [or not] of the Bloch Wall [central demilitarised zone] is then determined by holding the blunt end of the sewing needle [between two fingers] whilst [repeatedly] running the sharp tip of the sewing needle along the side of the cylinder magnet from pole to pole.


The experimental results clearly demonstrate:

1) The Bloch Wall is easily located at the centre of the cylinder magnet as the point where the magnet “tug” on the needle suddenly changes direction. The sudden switch of direction in the magnetic “tug” makes it difficult to position the tip of the needle exactly on the Bloch Wall.

2) Between the Bloch Wall and the North Pole the magnetic “tug” is towards the centre of the North Pole.

3) Between the Bloch Wall and the South Pole the magnetic “tug” is towards the centre of the South Pole.

Extending the experimentation by dangling the sewing needle by a piece of thread above the cylinder magnet enables the observation of the arching trajectories of the magnetic force and enables the Magnetic Lines of Force [for a cylinder magnet] to be clearly documented.

Magnetic Lines of Force

The illustration [based upon experimental results] clearly differs from mainstream magnetism.

The sceptical reader should simply replicate the experiment for themselves with a sewing needle that isn’t permanently magnetised.

Gallery | This entry was posted in Astrophysics, Geomagnetism, Magnetism, Science, Vortices. Bookmark the permalink.

One Response to Black and White Bloch

  1. Pingback: Inner Van Allan Zebra Stripes | MalagaBay

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