Engineering multiferroism through localized hole doping in a flat-band ferroelectric HfO₂

Area of Science:

• Materials Science
• Condensed Matter Physics
• Solid State Chemistry

Background:

• Ferroelectric hafnium oxide (HfO2) exhibits flat phonon bands and alternating polar/spacer layers.
• These polar layers possess switchable ferroelectric dipoles, making them promising for ultradense memory devices.

Purpose of the Study:

• To demonstrate the coupling of localized ferroelectric dipoles with electrically tunable magnetism.
• To achieve multiferroism in a Si-compatible ferroelectric material.

Main Methods:

• Density Functional Theory (DFT) simulations were employed to investigate nitrogen substitution in HfO2.
• Analysis focused on the electronic structure, magnetic ordering, and ferroelectric coupling.

Main Results:

• Nitrogen substitution preferentially occurred in the polar layer of HfO2.
• Nitrogen substitution created localized holes with magnetic moments, inducing antiferromagnetic (AFM) ordering.
• The AFM Néel vector is tunable by an external electric field via ferroelectric displacement.

Conclusions:

• A novel multiferroic compound was realized by exploiting hole doping localized in the polar layer of ferroelectric HfO2.
• This strategy leverages flat phonon bands for Si-compatible multiferroic materials.
• The findings open avenues for electric-field-controlled magnetic devices.