Light Controls Magnetism in Novel Altermagnetic Materials

Altermagnetism, a newly discovered magnetic order characterised by a unique spin-splitting band structure and zero net magnetisation, is rapidly becoming a focus of intense scientific investigation due to its potential for both fundamental discoveries and practical applications. Lijun Yang and Long Liang, both from Sichuan Normal University, now reveal a striking nonlinear opto-magnetic signature within these materials, specifically exploring how light can induce magnetisation. Their work demonstrates that linearly polarised light effectively controls the magnetisation direction, aligning it with the material’s Néel vector, and exhibits a predictable, periodic response dependent on the light’s polarisation. This discovery not only provides a novel method for manipulating altermagnetic materials, but also offers a powerful new technique for probing their underlying physical properties, opening avenues for advanced material characterisation and potential device development.

Light Induces Magnetization in Altermagnetic Materials

Scientists have investigated the opto-magnetic response of altermagnetism, focusing on the inverse Cotton-Mouton effect, a process where linearly polarized light induces static magnetization. This study pioneers a method for both manipulating and probing the unique properties of these materials, which possess fully compensated magnetic moments but exhibit spin-splitting in their electronic band structure. Researchers employed symmetry analysis and a detailed theoretical framework to understand how light interacts with the altermagnetic order. The experimental approach involved directing linearly polarized light onto altermagnetic samples and observing the resulting static magnetization, which depends critically on the polarization angle of the incident light, reflecting the underlying symmetry of the material, and aligns with the direction of the Néel order, providing a direct optical method for detecting this order.

This work demonstrates that altermagnets, unlike traditional antiferromagnets, are not invariant under combined time reversal and spatial inversion, allowing linearly polarized light to induce magnetization. Scientists estimated the magnitude of the induced magnetization for the altermagnet candidate KRu₄O₈, predicting its frequency and temperature dependence, and establishing the potential for efficient ultrafast optical control. The research highlights a significant departure from conventional magnetic materials, where such optical control is challenging, and opens new avenues for spintronics and information technology.

The induction of static magnetization via linearly polarized light is demonstrated. The direction of the induced magnetization aligns with the Néel vector, and its magnitude exhibits a periodic.

Altermagnetism, Light, and Magnetization Control

This work presents a theoretical investigation of the inverse Cotton-Mouton effect (ICME) in altermagnets, a recently discovered magnetic order characterized by zero net magnetization but possessing unique spin-splitting band structures. The research demonstrates that the ICME can be used both to manipulate the magnetization within these materials and to probe their fundamental properties, revealing that the direction of induced magnetization is governed by the Néel vector. Importantly, the magnitude of this induced magnetization exhibits a periodic dependence on the polarization angle of incident light, a clear signature of the material’s symmetry. The team developed a detailed theoretical framework of the ICME using symmetry analysis, estimating an induced magnetization of approximately 1%μB per unit cell for the candidate altermagnet KRu4O8. These findings highlight the potential of optical methods for controlling magnetism in altermagnets and gaining deeper insights into their intrinsic characteristics. While the study provides a strong theoretical foundation, the authors acknowledge that experimental verification is needed to fully validate the predictions and explore the effect in a wider range of altermagnetic materials.