page_title: Barkhausen effect
hierarchical_section_title: Barkhausen effect
caption_attribution_description: English: A replica of the experimental apparatus used by German physicist Heinrich Barkhausen in 1919 to detect the Barkhausen effect. This is a hissing or series of crackling sounds heard in an earphone attached to a coil of wire around an iron core when the magnetic field through it changes. When a magnet is brought near a piece of iron, the domain walls of the magnetic domains move, reorienting the domains so the , The sound is caused by the domain walls getting hung up on defects in the crystal lattice and then "snapping" past them. This effect is responsible for the magnetization hysteresis curve of the magnetic material. The apparatus consists of a coil of wire wound around an iron core (center) with the coil attached to a vacuum tube amplifier and a pair of earphones. A horseshoe magnet (right) that can be rotated by a knob is next to the iron. When the magnet is rotated by 180°, its magnetic field which passes through the iron core changes from one direction to the opposite direction. The Barkhausen noise is heard in the earphone while the magnet is being turned.
context_page_description: The Barkhausen effect is a name given to the noise in the magnetic output of a ferromagnet when the magnetizing force applied to it is changed. Discovered by German physicist Heinrich Barkhausen in 1919, it is caused by rapid changes of size of magnetic domains.
  Barkhausen's work in acoustics and magnetism led to the discovery, which became the main piece of experimental evidence supporting the domain theory of ferromagnetism proposed in 1906 by Pierre-Ernest Weiss. The Barkhausen effect is a series of sudden changes in the size and orientation of ferromagnetic domains, or microscopic clusters of aligned atomic magnets, that occurs during a continuous process of magnetization or demagnetization. The Barkhausen effect offered direct evidence for the existence of ferromagnetic domains, which previously had been postulated theoretically. Heinrich Barkhausen discovered that a slow, smooth increase of a magnetic field applied to a piece of ferromagnetic material, such as iron, causes it to become magnetized, not continuously but in minute steps.
context_section_description: The Barkhausen effect is a name given to the noise in the magnetic output of a ferromagnet when the magnetizing force applied to it is changed. Discovered by German physicist Heinrich Barkhausen in 1919, it is caused by rapid changes of size of magnetic domains (similarly magnetically oriented atoms in ferromagnetic materials).
  Barkhausen's work in acoustics and magnetism led to the discovery, which became the main piece of experimental evidence supporting the domain theory of ferromagnetism proposed in 1906 by Pierre-Ernest Weiss. The Barkhausen effect is a series of sudden changes in the size and orientation of ferromagnetic domains, or microscopic clusters of aligned atomic magnets (spins), that occurs during a continuous process of magnetization or demagnetization. The Barkhausen effect offered direct evidence for the existence of ferromagnetic domains, which previously had been postulated theoretically. Heinrich Barkhausen discovered that a slow, smooth increase of a magnetic field applied to a piece of ferromagnetic material, such as iron, causes it to become magnetized, not continuously but in minute steps.
caption: Replica of Barkhausen's original apparatus, consisting of an iron bar with a coil of wire around it (center) with the coil connected through a vacuum tube amplifier (left) to an earphone (not shown).  When the horseshoe magnet (right) is rotated, the magnetic field through the iron changes from one direction to the other, and the crackling Barkhausen noise is heard in the earphone.
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