Fabrication and magnetic properties of small FePt dot arrays

Abstract

FePt dot arrays with dot sizes ranging from 100 down to 15 nm were fabricated using sputtering, annealing and patterning techniques. The dot diameter distribution and dot position deviation are greater for smaller dot arrays than for larger dot arrays. The dot arrays produced through a sequence of annealing followed by patterning have a large perpendicular magnetic anisotropy resulting from the highly L10-ordered structure and the perpendicular orientation of the [0 0 1] crystalline axis, whereas samples of annealing after patterning display a magnetic vortex structure. As the dot size reduces from 100 to 29.9 nm, the arrays produced by annealing and then patterning exhibit an increase in the remanent coercivity H cr from 15.7 to 21 kOe because fewer defects are contained by the smaller dots. This result is explained by nucleation and domain wall propagation mechanisms. For 15.4 nm dot arrays, a model of dot with damaged edge may interpret the decreasing coercivity behaviour.

Towards an understanding of microstructure of patterned FePt dots by magnetometry using pulse fields

“…The preparation procedure of the FePt dot arrays consisting of film sputtering, annealing and patterning was described in detail previously [17,18]. In order to recover the dots from possible defects induced by the ion bombardments in the film patterning [20][21][22], post-fabrication thermal treatments were conducted systematically.…”

“…However, these additions often make the magnetic and structural analysis complicated after the film patterning. In our previous work, arrays of FePt dots smaller than 100 nm were investigated experimentally [18]. Besides the high PMA, large coercivity discrepancies between the experimental results and theoretical predictions were observed in the samples.…”

Understanding magnetic properties of arrays of small FePt dots with perpendicular anisotropy

“…After the annealing treatment at a relatively low temperature of 550 1C, the degree of order as high as 0.94 of the L1 0 -phase FePt in the continuous film was obtained. The array structure of the FePt dots was then made by electron beam lithography followed by ion etching, as described in detail in [13]. To improve the magnetic properties, the annealing process was carried out again on the arrays at 700 1C.…”

“…Because of the large magnetic anisotropy of the FePt dots, a homemade electromagnet device generating pulse magnetic fields was utilized to saturate the samples, while the opposite fields were applied by MOKE equipment [13]. Consequently, the remanent hysteresis loops could be constructed and the remanent coercivities H cr could be determined.…”

“…In addition, the dependences of the magnetic properties of the dot arrays on the preparation parameters were demonstrated, including the annealing temperature, the sequence of film patterning and annealing, and the patterning parameters. It is found that the procedure of film annealing followed by patterning can increase the array magnetic properties and the reversal of the dot is affected by the structure defects [13]. However, the discrepancy between the experimental results and theoretical predictions, origins of the SFD of the dot arrays, and the reversal mechanism of the dots remains unclear.…”