Abstract

Ferromagnetic/antiferromagnetic/ferromagnetic (FM/AF/FM) trilayers are investigated by polarized neutron reflectivity (PNR) with polarization analysis to obtain the layer resolved magnetization profile at various states of magnetization. The trilayers are composed of FeCoV (FM) layers which are separated by NiO (AF) layers of varying thickness. The spin-dependent reflectivities are analyzed by modeling the magnetic states of the FeCoV layers. First, we study magnetization configurations during the magnetization reversal as a function of AF thickness. It is found that for thin AF layers the magnetization reversal of the FM layers occurs simultaneously, whereas for thick AF layers the reversal occurs in a two-step process. In a second part of the experiments we follow, by PNR, the reorientation of the top FM layer in an in-plane perpendicular field starting from a state with the magnetization in the adjacent FM layers oriented antiparallel. It is observed that the magnetization of the top FeCoV layer gradually rotates into the direction of the applied field while the bottom FeCoV layer remains pinned in its state perpendicular to the field.

Keywords: Polarized neutron reflectometry; Magnetic depth profile; Magnetization reversal; Interlayer exchange coupling; Exchange bias

PACS: 61.12.Ha; 75.70.−i; 75.50.Ee

Article Outline

1. Introduction

2. Experiments

3. Results and discussion

Acknowledgements

References

(28K)
Fig. 1. XRR of FeCoV/NiO (t_NiO)/FeCoV trilayers. The symbols represent the experimental data whereas the solid lines show the computed reflectivities. The curves are shifted for clarity.

(26K)
Fig. 2. M–H loops of FeCoV/NiO (t_NiO)/FeCoV trilayers: for , the magnetization reversal occurs via a single process and for , it occurs in two steps. The arrows indicate the positions where PNR is measured (see Fig. 3).

(54K)
Fig. 3. PNR of FeCoV/NiO (t_NiO)/FeCoV trilayers measured at selected positions during the magnetization reversal as indicated in Fig. 2. Experimental data are represented by symbols: , R++; , R− −; ■, R+−; ○, R−+. Computed reflectivities are represented by lines. The insets show the average magnetization of individual FeCoV layers as obtained from modeling. Note that PNR is identical for the configurations which are mirrored at the field axis.

(38K)
Fig. 4. PNR of FeCoV/NiO (60 nm)/FeCoV trilayers measured at two different fields after preparing the sample in a state with the magnetization of the two FeCoV layers being antiparallel with respect to each other and perpendicular to the applied field. Experimental data are represented by symbols: , R++; , R− −; ■, R+−; ○, R−+. Computed reflectivities are represented by lines.

Table 1.
PNR results of FeCoV/NiO/FeCoV trilayers

Sample (tNiO)	5 nm	20 nm	60 nm
H [Oe]	150	100	110
Mt, [μB/f.u.]	−0.75	−0.69	+2.07
Mt,21/2 [μB/f.u.]	0.27	0.40	0.36
Mb, [μB/f.u.]	−0.56	−1.21	−1.60
Mb,21/2 [μB/f.u.]	0.21	0.70	0.58
M/Ms (PNR)	−0.3	−0.4	+0.1
M/Ms (bulk)	−0.2	−0.3	+0.1

H is the applied field. M_t(b):() are the parallel (perpendicular) components of the magnetic moments of the top (bottom) FeCoV layers, respectively ·denotes the lateral average within the coherence length of the neutron beam. M is the resulting net magnetic moment parallel to the applied field. Negative values indicate a component antiparallel to the field.

References

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Corresponding author. Tel.: +49 89 289 14725; fax: +49 89 289 14724.