[Paper Review] Altermagnetic multiferroics and altermagnetoelectric effect

Libor Šmejkal|arXiv (Cornell University)|Nov 29, 2024

Multiferroics and related materials14 citations

TL;DR

The paper uses first-principles calculations to show altermagnetic spin polarization in certain ferroelectrics, classifies altermagnetic polar spin groups, and proposes a nonrelativistic altermagnetoelectric coupling mechanism.

ABSTRACT

Magnetoelectric multiferroics are highly sought after for applications in low-power electronics and for advancing fundamental research, including axion insulators and dark matter detection. However, achieving a combination of ferroic spin and electric orders, along with their controllable switching, remains a significant challenge in conventional ferromagnets and antiferromagnets. Here, we present first-principles evidence that time-reversal symmetry-breaking altermagnetic spin polarization with relatively high critical temperatures can emerge in ferroelectrics BaCuF$_4$ (T$_N$ $\sim$ 275K) and Ca$_3$Mn$_2$O$_7$ (T$_N$ $\sim$ 110K). Furthermore, we classify all possible altermagnetic polar spin groups, revealing altermagnetism in a collinear phase of BiFeO$_3$. We also propose an altermagnetoelectric effect, a nonrelativistic cross-coupling between altermagnetic spin polarization and ferroelectric polarization, mediated by a rotation of nonmagnetic polyhedra in the lattice structure. Our findings suggest an alternative pathway towards high-temperature magnetoelectric multiferroicity and the electric field control of altermagnetic order parameters.

Motivation & Objective

• Demonstrate time-reversal symmetry-breaking altermagnetic spin polarization in ferroelectrics with relatively high critical temperatures.
• Classify all possible altermagnetic polar spin groups, including a case in BiFeO3.
• Propose an altermagnetoelectric effect as a nonrelativistic cross-coupling mechanism between altermagnetic and ferroelectric orders.
• Explore implications for high-temperature magnetoelectric multiferroicity and electric-field control of altermagnetic order parameters.

Proposed method

• Perform first-principles calculations to identify altermagnetic spin polarization in BaCuF4 (T_N ~275 K) and Ca3Mn2O7 (T_N ~110 K).
• Classify altermagnetic polar spin groups and identify altermagnetism in a collinear phase of BiFeO3.
• Propose and articulate a nonrelativistic altermagnetoelectric coupling mechanism mediated by rotation of nonmagnetic lattice polyhedra.

Experimental results

Research questions

• RQ1 Can altermagnetic spin polarization arise in ferroelectric materials at experimentally relevant temperatures?
• RQ2 Which crystallographic groups support altermagnetic polarization, and is altermagnetism present in BiFeO3?
• RQ3 Is there a viable altermagnetoelectric coupling mechanism that links altermagnetic and ferroelectric orders?
• RQ4 What are the implications for achieving high-temperature magnetoelectric multiferroicity and electric-field control of altermagnetic order?

Key findings

• First-principles evidence of time-reversal symmetry-breaking altermagnetic spin polarization in BaCuF4 (T_N ~275 K) and Ca3Mn2O7 (T_N ~110 K).
• Classification of altermagnetic polar spin groups, with altermagnetism identified in a collinear BiFeO3 phase.
• Introduction of an altermagnetoelectric effect as a nonrelativistic cross-coupling between altermagnetic and ferroelectric orders.
• Proposed mechanism where the coupling is mediated by rotation of nonmagnetic lattice polyhedra.