Structural properties of molecular beam epitaxy grown Ni/Pt superlattices

Abstract

We find that the [Ni 3.2nm Pt 1.6nm ] 3 15 and [Ni 3.2nm Pt 0.8nm ] 3 15 multilayers are semicoherent and display a columnar morphology. From both the period of the moiré fringes and the positions of the diffraction peaks in electronic (plan-view and crosssection geometries) and x-ray diffraction patterns, one deduces that the nickel is relaxed (at least in the error bars of all our measurements), whereas the platinum remains slightly strained ͑ഠ21%͒. The interfaces are sharp; no intermixing takes place giving rise to neat contrasts in transmission electron microscopy (TEM) and to high intensities of the superlattice peaks in the growth direction in both diffraction techniques. The relaxation of the interfacial misfit occurs partially through misfit dislocations, partially through the strain of platinum. A quasiperiodic twinning occurs at the interfaces, the stacking fault which forms the twin being the most often located at the interface Pt͞Ni, i.e., when a Pt layer begins to grow on the Ni layer. The simulation of the u͞2u superlattice peak intensities takes into account the columnar microstructure. It shows that the roughness is predominantly at medium scale with a fluctuation of about 12.5% for Ni layers and negligible for Pt layers.

Layer-Resolved Magnetic Moments inNi/PtMultilayers

“…These effects may be attributed to hybridization at the Ni͞Pt interface. They are much less pronounced in the second from the interface Ni and Pt layers indicating sharp interfaces in agreement with the structural studies [7][8][9].…”

“…For this profile two series of Ni n ͞Pt m samples, one with constant m 5 and n 2, 4, 6 and another with constant n 6 and m 2, 5 were used. Contrary to alloys where the atomic distances are strongly dependent on their composition, for thick multilayers with large lattice misfit ͑ϳ10%͒ between their constituents, like ours, it has been shown that the constituents retain almost their bulk lattice parameters and the residual strain is very small ͑0% 2%͒; see, e.g., [8,19]. Thus, one may not expect sizable changes of the volume of Pt and Ni in our samples due to their composition which could have affected the spin magnetic moment [20] and, consequently, the determination of the magnetic profile by using various samples [21].…”

“…As a prototype system we select the Ni͞Pt one because (i) the interfaces between Ni and Pt in evaporated Ni͞Pt multilayers are sharp in the ML limit, as was shown by structural characterization via x-ray diffraction (XRD) and electron microscopy [7,8]. As evidence we show in Fig.…”

X-ray magnetic circular dichroic magnetometry on Ni/Pt multilayers

“…Inside the grains, the interfaces are flat and roughness could be at the maximum about 1 to 2 ML. 5,16 This interface roughness has to be clearly distinguished from interdifussion. Roughness of 1 to 2 ML could be accompanied by a a͒ Author to whom correspondence should be addressed; Tel: ͑ϩ4930͒838-56143, Fax: ͑ϩ4930͒838-53646, electronic mail: babgroup@physik.fuberlin.de large ͑several nm͒ lateral coherence of pure Ni or Pt layers, while in the case of interdifussion the lateral coherence is only 1 to 2 lattice parameters.…”

Magnetic studies in evaporated Ni/Pd multilayers

“…It is shown that the thermal decrease of the spontaneous magnetization of ferromagnetic transition metal differs characteristically depending on preparation conditions [2][3][4][5][6]. In all cases, the deviations from saturation at absolute zero can be accurately described by a single temperature power, temperature power term T n , which holds up to several hundreds of kelvins.…”