Visualization of the Barkhausen Effect by Magnetic Force Microscopy

Abstract

By visualization of the Barkhausen effect using magnetic force microscopy we are able to provide detailed information about the physical principles that govern the magnetization reversal of a granular ferromagnetic thin film with perpendicular anisotropy. Individual Barkhausen volumes are localized and distinguished as either newly nucleated or grown by domain wall propagation. The Gaussian size distribution of nucleated Barkhausen volumes indicates an uncorrelated random process, while grown Barkhausen volumes exhibit an inverse power law distribution, which points towards a critical behavior during domain wall motion.

Universality classes and crossover scaling of Barkhausen noise in thin films

“…Figure 6(a) shows the resulting s χ (λ) data, which can be well fitted by an exponential, thus confirming the functional form in Eq. (11). Estimating the value of the crossover roughness exponent ζ χ in Eq.…”

“…In three-dimensional bulk ferromagnetic materials, the scaling behavior of the Barkhausen effect is understood theoretically in terms of the depinning transition of domain walls [3] with two distinct universality classes for amorphous and polycrystalline materials [4]. A similar clear-cut classification does not exist in lower dimensions, despite Barkhausen avalanches having been studied experimentally for decades in several ferromagnetic thin films with in-plane [5][6][7][8][9][10] or out-of-plane anisotropy [11,12]. This issue is particularly important because these lowdimensional magnetic structures have become increasingly relevant for various technological applications [13,14].…”

Imprinted labyrinths and percolation in Nd-Co/Nb magnetic/superconducting hybrids

“…15 The ferromagnetic layer in the hybrid bilayers is made of NdCo 5 , an amorphous alloy with saturation magnetization M S ¼ 1.4 Â 10 3 emu/cm 3 at 10 K. 16 Out of plane hysteresis loops present typical saturation fields H sat out-of-plane in the 5-10 kOe range, depending on sample thickness, well below the shape anisotropy field 4pM s ¼ 18 kOe indicating the existence of a moderate out-of-plane anisotropy K n within the layers. 16 The effective PMA constant, K n , can be estimated from H sat in-plane ¼ 25 kOe, the saturation field of an in-plane hysteresis loop measured in a 80 nm thick film, 16 3 . Thus, we may estimate the anisotropy ratio as Q ¼ K n /2pM s 2 % 1.4.…”

“…1 Depending on magnetic history and material parameters, a variety of configurations can be observed during the magnetization reversal process ranging from ordered arrays of parallel stripe domains to disordered labyrinthine structures. 2 Different experimental techniques such as magnetic force microscopy (MFM) 3 or X-ray microscopy 4 and theoretical models 5 have shown how the interplay between magnetic anisotropy, dipolar interactions, and disorder affects critically the physics of reverse domain nucleation and expansion and the resulting domain structure.…”

A model for the Barkhausen frequency spectrum as a function of applied stress

“…If the strength of coupling between adjacent magnetic domains and the degree of randomness in the pinning potential reach some critical value, the shapes of avalanches with different durations become similar, exemplifying scale invariance. [1][2][3][4][5][6][7][8][9][10] This type of behaviour is a result of Brownian correlations in the pinning potential and can be quantified by power-law functions. These dynamics are also reflected in the power spectrum of Barkhausen emissions, which, at the lower end scales as approximately 1=x 2 in the Alessandro-BeatriceBertotti-Montorsi (ABBM) model 11,12 and from 1=x 1:3 to 1=x 2 in the Random Field Ising (RFI) model, depending on the strength of dipolar interactions.…”