In our studies we investigated the influence of the proximity of the antiferromagnetic CoO layer on the magnetic properties of ultrathin wüstite (FeO) films. Comparative Mössbauer spectroscopy measurements for MgO/FeO/MgO(001) and MgO/FeO/CoO/MgO(001) show that the neighboring CoO layer can significantly enhance the ordering temperature of wüstite. The T_N of CoO in the FeO/CoO bilayer was determined with a use of X-ray magnetic linear dichroism (XMLD) measurements.

Antiferromagnets (AFMs) due to their unique properties are promising candidates for the next generation spintronic materials [1], [2]. A wide group of AFM materials seems to be useless for applications due to the low ordering temperature, above which the long-range antiferromagnetic order vanishes. The limitation of low T_N can be overcome using the magnetic proximity effect [3].

Synchrotron SOLARIS users proved, that the proximity of CoO strongly influences the magnetic properties of the FeO layer. For the FeO layers grown on 2 nm-thick CoO, the ordering temperature of FeO was increased by 100 K due to the magnetic proximity. This result shows that the limitation of the low ordering temperature of wüstite can be overcome by the antiferromagnetic proximity. To determine the T_N of CoO in the FeO/CoO bilayer, we performed x-ray magnetic linear dichroism (XMLD) measurements. X-ray absorption spectra (XAS) were collected at the PIRX beamline of the National Synchrotron Radiation Centre SOLARIS. Figure 1 shows exemplary normalized XAS spectra for a CoO thickness of 2 nm in FeO/CoO, collected under normal and 60^o X-ray incidence angles at 80 K. Systematic studies of CoO XAS spectra as a function of temperature enabled us to determine the T_N of CoO in FeO/CoO bilayer.

Fig. 1. Co L3 edge XAS spectra at φ = 0° (black solid line) and φ = 60° (red dashed line) obtained for FeO/CoO at 80 K. Inset shows the measurement geometry. (source: Appl. Phys. Lett. 120, 072404 (2022)).

Read the full publication:

A. Kozioł-Rachwał et al., Beating the Limitation of the Néel Temperature of FeO with Antiferromagnetic Proximity in FeO/CoO, Appl Phys Lett 120, 072404 (2022). 

[1] V. Baltz, A. Manchon, M. Tsoi, T. Moriyama, T. Ono, and Y. Tserkovnyak, Antiferromagnetic Spintronics, Rev Mod Phys 90, 15005 (2018).

[2] P. K. Manna and S. M. Yusuf, Two Interface Effects: Exchange Bias and Magnetic Proximity, Phys Rep 535, 61 (2014).

[3] D. Hou, Z. Qiu, and E. Saitoh, Spin Transport in Antiferromagnetic Insulators: Progress and Challenges, NPG Asia Mater 11, 35 (2019).

Written by: Dr. Anna Kozioł-Rachwał