Modification of Co/Pt multilayers by gallium irradiation—Part 1: The effect on structural and magnetic properties

Abstract

Atomic force microscopy, transmission electron microscopy, optical, and magneto-optical microscopy have been used to study how structural and magnetic properties are changed when a Co/Pt multilayer is quasihomogeneously irradiated with Ga ions. Under low irradiation fluence, both grain size and texture in the multilayer increase. These effects continue for fluences in excess of 1ϫ10 15 Ga ions/cm 2 , but beyond this dose significant thinning of the multilayer is also observed. Three distinct irradiation-induced magnetic regimes with sharp transitions between each were identified. For Ga fluences less than 5ϫ10 12 ions/cm 2 , the irradiated region retains perpendicular uniaxial anisotropy but with coercivity lower than that of the as-grown film. For fluences between 5ϫ10 12 and 1ϫ10 13 Ga ions/cm 2 , a transition from perpendicular to in-plane magnetization was experienced. Very little change of the in-plane magnetic properties of irradiated multilayers is then observed until the sample experiences a ferromagnetic to paramagnetic transition at fluences around 1ϫ10 15 Ga ions/cm 2 . A brief comparison with the effect of irradiating with He ions is given.

Modification of Magnetic Properties of Pt/Co/Pt Films by Ga+ Ion Irradiation: Focused versus Uniform Irradiation

“…The optical reflectivity in uniformly irradiated (100 × 100 µm 2 ) square areas is progressively reduced when increasing the fluence, in agreement with the enhancement of the film transmission associated with sample etching [29]. As previously checked [37] and presently confirmed by AFM on a uniformly irradiated sputtered film, the surface roughness was slightly enhanced by a factor of about two between F = 0 and F = 7 × 10 14 Ga + ions/cm 2 .…”

“…In the quasi-uniform mode, the FIB is rapidly scanned over all the investigated film area. Some preliminary results were reported for sputtered Co (d Co = 1.4 nm) [13,29] and Co (d Co = 2.6 nm) [16] films. We evidenced rather similar magnetic changes by both irradiation procedures at comparable estimated fluences while the incoming Ga + ion rate in a nanosize region is much higher for the FIB procedure than for uniform irradiation.…”

“…Further increase of the fluence F results in: (i) decrease of both hysteresis and amplitude of magnetization loop, see Fig. 2f for F ≈ 10 16 Ga + ions/cm 2 ; (ii) sample etching which could be determined from simulations and experiments [29]. Before final nanostructure etching, the samples undergo transition into superparamagnetic state -separated magnetic grains in nonmagnetic matrix.…”

Ga+ion irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt thin film studied by X-ray magnetic circular dichroism

“…Among them, the control of magnetic anisotropy by ion irradiation has attracted much interest in this decade [1][2][3][4][5][6][7][8][9], due to a possibility of nanostructure patterning by using a focused ion beam [3,5]. In fact, a Ga + -induced spin reorientation transition to perpendicular magnetization from an inplane magnetized Pt/Co/Pt thin film has been reported at medium ion fluences in the 10 14 ions/cm 2 region [1].…”

Precise control of domain wall injection and pinning using helium and gallium focused ion beams

“…The influence of high energy ion irradiation on magnetic properties has been widely studied in the past, first using Ga ions 12 and He ions 13,14 and more recently with highly focused Ga beams. 15,16 However, very recently also helium ion microscopy (HIM) systems have become commercially available, using a focused He beam that has several advantages for imaging and nanostructuring, the most notable advantage being the subnanometer resolution.…”