# Epitaxial growth and characterization of (001) [NiFe/M]$_{20}$ (M = Cu, CuPt and Pt) superlattices

## TL;DR

This study optimizes the growth of (001) NiFe/M superlattices on MgO substrates, analyzing how epitaxial strain influences magnetic anisotropy and coercivity, revealing strain-induced rotation of easy magnetization axes and isotropic magnetic behavior.

## Contribution

It demonstrates controlled epitaxial growth of NiFe/M superlattices with strain-dependent magnetic properties, providing insights into strain effects on magnetocrystalline anisotropy.

## Key findings

- Epitaxial growth achieved at 100°C regardless of lattice mismatch.
- Epitaxial strain causes rotation of magnetic easy axes from [110] to [100].
- Increased strain leads to isotropic magnetic hysteresis and higher coercivity.

## Abstract

We present optimization of [(15 $\unicode{x212B}$) Ni$_{80}$Fe$_{20}$/(5 $\unicode{xC5}$) M]$_{20}$ single crystal multilayers on (001) MgO, with M being Cu, Cu$_{50}$Pt$_{50}$ and Pt. These superlattices were characterized by high-resolution X-ray reflectivity (XRR) and diffraction (XRD) as well as polar mapping of important crystal planes. It is shown that cube on cube epitaxial relationship can be obtained when depositing at the substrate temperature of 100 $^\circ$C regardless of the lattice mismatch (5% and 14% for Cu and Pt, respectively). At lower substrate temperatures poly-crystalline multilayers were obtained while at higher substrate temperatures {111} planes appear at $\sim$10$^\circ$ off normal to the film plane. It is also shown that as the epitaxial strain increases, the easy magnetization axis rotates towards the direction that previously was assumed to be harder, i.e. from [110] to [100], and eventually further increase in the strain makes the magnetic hysteresis loops isotropic in the film plane. Higher epitaxial strain is also accompanied with increased coercivity values. Thus, the effect of epitaxial strain on the magnetocrystalline anisotropy is much larger than what was observed previously in similar, but polycrystalline samples with uniaxial anisotropy (Kateb et al. 2021).