Magnetic moment fluctuations in samples with near-to-rectangular hysteresis loops

Abstract

Soft magnetic materials with high permeance are usually used in the development of sensors for low magnetic fields. When the sensor is excited with an alternating magnetic field of frequency ƒ 0, the minimum detectable external magnetic field depends on the magnetic noise level in the sensor. These noises are usually connected both with the Barkhausen effect and with ‘1/ƒ’ noise. The former has a relatively uniform spectral distribution up to frequencies equal to the inverse mean Barkhausen discontinuity duration when the latter has the spectral distribution concentrated around harmonics of the exciting frequency in the sensor response. It is shown in this paper that the spectral distribution of magnetic moment fluctuations can be modulated with the oscillating function depending on frequency with gaps adjacent to even harmonics. These modulations are connected with the magnetic moment change correlation on different exciting field cycles and should become most apparent in samples with near-to-rectangular hysteresis loops. An experiment with a single-axis polycrystalline magnetic Fe-Ni film produced by vacuum deposition of metal on a hot glass layer has confirmed the existence of such a modulation. The number of cycles with correlated magnetic moment fluctuations has been estimated. The correlation increases at higher ƒ 0. It has been shown that the 1/ƒ noise in samples with near-to-rectangular hysteresis loops is generated due to the presence of ‘hard’ domains that do not remagnetize with frequency ƒ 0 and have stochastically wandering bounds that determine the coercive force and top magnetization fluctuations. The potential relief responsible for quasi-stable states of the equilibrium location of domain bounds is due to local internal strains at crystalline defects.