Local magnetization profile and geometry magnetization effects in microwires as determined by magneto-optical Kerr effect

Abstract

The local magnetization profile along the length in magnetostrictive Fe-based magnetic microwires has been determined by magneto-optical Kerr effect. The study has been performed in microwires with different geometrical dimensions (i.e., diameter and length). The profiles of remanent magnetization and coercivity remain constant at the middle part for all microwires, whereas significant reduction of net magnetization accompanied by significant change of coercivity is observed when approaching their ends. This local region extends just few tens of micrometer for thin (around 1 μm diameter) wires and up to several hundreds of micrometer for thick (around 10 μm diameter) wires. That predicts that critical length to observe bistability goes from 50 μm to nearly 1 mm as diameter increases from 1 to 10 μm. Results are further interpreted considering the local distribution of magnetic charges at the ends which, arising to reduce stray fields, lead in some cases to inverted loops.

Controlled single-domain wall motion in cylindrical magnetic microwires with axial anisotropy

“…This indicates .3 VSM hysteresis loops for a 9-mm-long microwire with metallic diameter of 12 mm, and after cutting into pieces of reduced indicated length (after Ye et al, 2013). The closure structure reduces continuously its length from L c ¼ 0.66 to 0.43 mm as the length of the wire's pieces is reduced from 9 to 3 mm.…”

“…With respect to the influence of diameter, hysteresis loops were taken for 5-mmlong FeSiB microwires with metallic diameter d met ¼ 1.5 and 12 mm, and total diameter of around D T ¼ 20 mm (Ye et al, 2013). The microwire with smaller (1.5 mm) diameter exhibits a magnetically harder behavior, with smaller fractional remanence, M r /M s , and a larger coercivity (H c ¼ 1500 A/m) than the 12-mm wire (H c ¼ 110 A/m).…”

“…The longitudinal magnetization profile at remanence was earlier investigated (Zhukov et al, 1995) making use of fluxmetric induction method and a movable tiny search pickup coil. The magnetic response in a local region as small as few micrometers (Ye et al, 2013) can be obtained using the optimized longitudinal magneto-optical Kerr effect (NanoMOKE 2 by Durham Magnetooptics Ltd.). Specific studies have also been performed making use of the magneto-optical Kerr effect (MOKE).…”

Vortex magnetic structure in circularly magnetized microwires as deduced from magneto-optical Kerr measurements

“…20,21 The axial magnetization profile has been determined allowing one to unveil the complex magnetic domain structure near the ends of positive magnetostriction microwires. 22 In negative magnetostriction microwires, the nucleation of circular domains has been successfully driven with alternating electric current excitation over a wide range of frequencies and amplitudes of the magnetic field pulse. 23 Although a number of studies have been performed specifically on the role played by the negative magnetostriction value and the strength of the stresses coming from the Pyrex coat of variable thickness, there are still some open questions.…”

“…The magnetization processes at the two regions close to the ends of magnetic wires are typically different. 22 The difference comes from a different local domain structure owing to: (i) magnetostatic stray fields energy minimization, (ii) the presence of local defects (the very end of the microwire can be considered as the main defect), and (iii) in the case of glass-coated amorphous microwires, different stress distribution. Figure 4 shows LMOKE and TMOKE magnetic loops acquired simultaneously at 40 lm distance from the end of the microwire.…”