02_enhancement


Morales and Villagonzalo

6

Enhancement of Fe Magnetic Moments in Fe/Co (001) Multilayers

Marienette B. Morales*1 and Cristine R. Villagonzalo
Structure and Dynamics Group,

National Institute of Physics, University of the Philippines,
Diliman, Quezon City 1101

E-mail: mmorales@ateneo.edu

ABSTRACT

Science Diliman (July-December 2004) 16:2, 6–7

In order to investigate the electronic and magnetic properties of a bcc Fe/Co (001) multilayer, we have
performed electronic structure calculations employing the total energy full-potential linear muffin tin
orbital method. The magnetic moments of the layers are calculated. Based on these results, the
magnetization profiles and the microscopic origin of the enhancement of Fe moments in the multilayers of
the same Co content but with different interface qualities are reported. Large enhancement of magnetic
moment is observed in the Fe monolayer located at the interface, and an even greater increase is obtained
for the multilayer with one monolayer of intermixing between Fe and Co layers. The Co atoms were
found to have similar magnetic moments in the bulk and at the interface.

INTRODUCTION

Thin films are well known to exhibit features that are
not observed in bulk materials. A lot of work has been
devoted to the study of bcc Co thin films and Fe/Co
multilayers primarily for their great importance in
investigating magnetism of surfaces and interfaces in
unique structures. In this present work, the effects of
interface quality to the magnetic moment of the
constituent atoms in the multilayer are investigated. We
have chosen to study magnetism in a multilayer
consisting of Fe and Co, both of which are
independently highly ferromagnetic, and their positions
in the bcc lattice. An advantage of the Fe/Co system is
that it makes it possible to investigate Co atoms in the
bcc phase.

NUMERICAL METHOD

The computational method used is the full-potential
linear muffin tin orbital (FP-LMTO) method based on
the density-functional theory. This provides the basis
set in which the wave functions are expanded by
dividing the three-dimensional space into
nonoverlapping muffin-tin (MT) spheres region and
interstitial region. In each MT assigned to each atomic
site, the density and potential are expanded using
spherical harmonics, while outside the basis are
expanded by means of Fourier series. The main input
parameters are only the type of atoms and the structure
of the system of atoms, which are information that have
long been established or may be patterned from
experimental results. The advantage of this method is
that no approximation is made on the shape of the
density or potential.

STRUCTURAL PARAMETERS

The supercell or the smallest volume of the infinitely
periodic multilayer system is composed of eight atoms

*Corresponding author
1Ms. Morales is also from the Department of Physics of the Ateneo
de Manila University.



Enhancement of Fe

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which are stacked along the (001) axis. The atoms form
four conventional bcc unit cells with eight layers. The
unit cell is perfectly cubic so the in-plane and out-of-
plane lattice constants are equal at the numerically
verified value of 5.20 Bohr. To simulate the
experimentally observed imperfect interfaces in
fabricated Fe/Co multilayers, the atoms in the supercell
containing 25% Co concentration are rearranged such
that Co atoms are intermixed within the Fe layers.

SUMMARY OF RESULTS

We have successfully verified theoretically the
enhancement of the magnetic moment of Fe in Fe/Co
(001) multilayer in the ground state without any
restrictive assumptions. For multilayers with the same
content concentration, the location of atoms in the
multilayers affects the magnetic moment. Fe atoms that
are sandwiched between two Co atoms show an even
larger increase in magnetic moment than when placed
adjacent to another Fe layer and Co. For the Fe
monolayer, we have shown that this is due to the
presence of a different kind of atom as its nearest
neighbor. No significant change in Co moment is
observed even when the number of neighboring Fe and
Co atoms changes. These information are useful for
multilayer devices where a large magnetic moment
response is needed.