<p>Using a realistic model relevant to La<sub>2</sub>CuO<sub>4</sub> and other altermagnetic perovskites, we study interrelations between weak spin ferromagnetism, anomalous Hall conductivity, <i>σ</i><sub><i>x</i><i>y</i></sub>, and net orbital magnetization <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\mathcal{M}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi class="MJX-tex-caligraphic" mathvariant="script">M</mi> </math></EquationSource> </InlineEquation>. All of them are intertwined with the vector of Dzyaloshinskii-Moriya interactions. Nevertheless, while weak spin ferromagnetism is induced by interactions having the same sign in all equivalent bonds, <i>σ</i><sub><i>x</i><i>y</i></sub> and <InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({\mathcal{M}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi class="MJX-tex-caligraphic" mathvariant="script">M</mi> </math></EquationSource> </InlineEquation> are related to sign-alternating interactions, which do not contribute to any canting of spins. The microscopic model remains invariant under the symmetry operation <InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\{{\mathcal{S}}| {\bf{t}}\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>{</mo> <mrow> <mi class="MJX-tex-caligraphic" mathvariant="script">S</mi> <mo>∣</mo> <mi mathvariant="bold">t</mi> </mrow> <mo>}</mo> </mrow> </math></EquationSource> </InlineEquation>, combining the shift <b>t</b> of antiferromagnetically coupled sublattices to each other with the spin flip <InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({\mathcal{S}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi class="MJX-tex-caligraphic" mathvariant="script">S</mi> </math></EquationSource> </InlineEquation>. Thus, the band structure remains spin-degenerate, but the time-reversal symmetry is broken, providing a possibility to realize <i>σ</i><sub><i>x</i><i>y</i></sub> in antiferromagnetic substances. The altermagnetic splitting of bands, breaking <InlineEquation ID="IEq5"> <EquationSource Format="TEX">\(\{{\mathcal{S}}| {\bf{t}}\}\)</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mo>{</mo> <mrow> <mi class="MJX-tex-caligraphic" mathvariant="script">S</mi> <mo>∣</mo> <mi mathvariant="bold">t</mi> </mrow> <mo>}</mo> </mrow> </math></EquationSource> </InlineEquation>, does not play a major role in the problem. More important is the orthorhombic strain, responsible for finite <i>σ</i><sub><i>x</i><i>y</i></sub> and <InlineEquation ID="IEq6"> <EquationSource Format="TEX">\({\mathcal{M}}\)</EquationSource> <EquationSource Format="MATHML"><math> <mi class="MJX-tex-caligraphic" mathvariant="script">M</mi> </math></EquationSource> </InlineEquation>.</p>

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Altermagnetism and weak ferromagnetism

  • Igor Solovyev,
  • Sergey Nikolaev,
  • Akihiro Tanaka

摘要

Using a realistic model relevant to La2CuO4 and other altermagnetic perovskites, we study interrelations between weak spin ferromagnetism, anomalous Hall conductivity, σxy, and net orbital magnetization \({\mathcal{M}}\) M . All of them are intertwined with the vector of Dzyaloshinskii-Moriya interactions. Nevertheless, while weak spin ferromagnetism is induced by interactions having the same sign in all equivalent bonds, σxy and \({\mathcal{M}}\) M are related to sign-alternating interactions, which do not contribute to any canting of spins. The microscopic model remains invariant under the symmetry operation \(\{{\mathcal{S}}| {\bf{t}}\}\) { S t } , combining the shift t of antiferromagnetically coupled sublattices to each other with the spin flip \({\mathcal{S}}\) S . Thus, the band structure remains spin-degenerate, but the time-reversal symmetry is broken, providing a possibility to realize σxy in antiferromagnetic substances. The altermagnetic splitting of bands, breaking \(\{{\mathcal{S}}| {\bf{t}}\}\) { S t } , does not play a major role in the problem. More important is the orthorhombic strain, responsible for finite σxy and \({\mathcal{M}}\) M .