Tailoring interface alloying and magnetic properties in (111) Permalloy/ Pt multilayers

• We demonstrate preparation and characterization of permalloy Ni80Fe20 at.% (Py) multilayers in which the Py layers were deposited by two different sputter deposition methods. Namely, dc magnetron sputtering (dcMS) and high power impulse magnetron sputtering (HiPIMS), that represent low and moderate ionized flux fraction of the film forming material, respectively. We deposited ultrathin bilayers, i.e. 15 angstrom thick Py and 5 angstrom thick Pt, with 20 repetitions. Various effects such as substrate roughness, working gas pressure and sputter power are considered. The microstructure, texture and strain were characterized by X-ray diffraction, individual thicknesses and alloying were analysed by X-ray reflectivity, and uniaxial in-plane anisotropy probed by the magneto-optical Kerr effect. It is shown that HiPIMS deposition produces multilayers with reduced surface roughness regardless of the substrate surface roughness. Both dcMS and HiPIMS deposition present multilayers with strong (111) texture normal to the substrate. Using HiPIMS for deposition of the Py layer minimizes the alloying between individual layers compared to dcMS deposition performed at same average sputter power. However, this improvement in interface sharpness leads to a higher magnetic coercivity and a poor hard axis in the film plane. On the other hand, multilayers with alloying present a linear hard axis. Furthermore, we studied Py/Cu and Py/CuPt multilayers, prepared under identical conditions using HiPIMS. The results indicate that in the Py/Pt case, deterioration of the in-plane uniaxial anisotropy, is caused by inverse magnetostriction originating from the large lattice mismatch between Py and Pt. The Py/Pt multilayers that exhibit alloying have a less strained interface and have a well defined uniaxial anisotropy.

Ämnesord

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

Nyckelord

Permalloy

Pt

HiPIMS

Uniaxial anisotropy

Intermixing

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