Disorder mediated fully compensated ferrimagnetic spin-gapless semiconducting behaviour in Cr3Al Heusler alloy

summary

The gist

Spin-gapless semiconductors (SGSs) that simultaneously host fully compensated ferrimagnetism are highly sought for energy-efficient and stray-field-free spintronic technologies, yet their realization

In short

Researchers investigated Cr3Al, a chemically disordered Heusler alloy, to find a material exhibiting both spin-gapless semiconducting transport and fully compensated ferrimagnetism simultaneously. The study confirmed that this coexistence occurs in the fully A2-disordered structure. This discovery suggests that chemical disorder can stabilize functional electronic and magnetic states for advanced spintronic applications.

Key concepts

Spin-Gapless Semiconducting Transport (SGS): This transport behavior is characterized by weak temperature dependence in conductivity and very low Seebeck coefficients. It is driven by chemical disorder, leading to an electron-hole compensated transport mechanism where the energy gaps are small and sensitive to disorder.
Fully Compensated Ferrimagnetism (FCF): The material exhibits a magnetic ground state where the net magnetization is almost zero. This is confirmed by neutron diffraction and XMCD measurements showing a net zero total magnetic moment on Cr atoms, pointing toward an antiferromagnetic or fully compensated ferrimagnetic ordering.
A2-type Disorder in Heusler Structure: Cr3Al adopts a structure with complete mixing of Cr and Al atoms at all atomic sites. This A2-type disorder arises because the atomic radii and electronegativities of Cr and Al are comparable, significantly influencing the alloy's electronic, magnetic, and transport properties.
Spin-Polarized Density Functional Theory (DFT): First-principles calculations using DFT were used to validate experimental findings. These simulations showed a vanishing spin-up band gap—a key indicator of SGS behavior—and predicted the almost zero net moment through antiparallel Cr spin configurations across mixed sites.

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This episode discusses

Disorder mediated fully compensated ferrimagnetic spin-gapless semiconducting behaviour in Cr3Al Heusler alloy · Paper Radio

The paper

Disorder mediated fully compensated ferrimagnetic spin-gapless semiconducting behaviour in Cr3Al Heusler alloy · Read on arXiv

Department of Physics, Indian Institute of Technology Palakkad, Kerala 678623, India · Department of Physics, Indian Institute of Technology Bombay, Mumbai 400076, India · Department of Chemistry, Indian Institute of Technology Kharagpur, West Bengal, India · Central University of Haryana · School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram-695551, India · UGC-DAE Consortium for Scientific Research Indore 452001, India · Solid State Physics Division, Bhabha Atomic Research Centre Mumbai 400085, India · Homi Bhabha National Institute Anushaktinagar Mumbai 400094, India

Spin-gapless semiconductors (SGSs) that simultaneously host fully compensated ferrimagnetism are highly sought for energy-efficient and stray-field-free spintronic technologies, yet their realization in chemically disordered systems has remained elusive. Here, we demonstrate that the binary Heusler alloy Cr3Al despite adopting a fully A2-disordered structure exhibits a rare coexistence of SGS transport and a fully compensated ferrimagnetic (FCF) ground state. Single-crystalline and polycrystalline Cr3Al samples were synthesized, and comprehensive structural analyses using single crystal XRD, synchrotron powder XRD, and neutron powder diffraction reveal complete Cr/Al site mixing. Remarkably, this chemical disorder does not disrupt magnetic order; instead, magnetization, X-ray magnetic circular dichroism (XMCD), and temperature-dependent neutron diffraction establish a robust compensated ferrimagnetic state with a vanishingly small ordered moment of 0.1(1) muB/f.u and a high Curie temperature of 773(2) K. Electrical and thermal transport measurements uncover clear SGS characteristics, including weak temperature-dependent conductivity, very low Seebeck coefficients, and electron-hole compensated transport. Hall measurements show unusual temperature-dependent carrier concentrations consistent with disorder-modified electronic states. First-principles calculations on an A2-disordered SQS structure reproduce the experimentally observed negligibly small magnetization (0.0072 muB/f.u) and reveal a vanishing spin-up band gap unambiguously supporting SGS behavior driven by chemical disorder. Our results identify Cr3Al as the first experimentally verified A2-disordered Heusler alloy exhibiting both fully compensated ferrimagnetism and spin-gapless semiconducting transport, positioning it as a robust and disorder-tolerant platform for next-generation, high-temperature spintronic devices.

DOI: 10.1002/adfm.75194

Transcript

Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: Today's paper: "Disorder mediated fully compensated ferrimagnetic spin-gapless semiconducting behaviour in Cr3Al Heusler alloy".

Mira: Spin-gapless semiconductors (SGSs) that simultaneously host fully compensated ferrimagnetism are highly sought for energy-efficient and stray-field-free spintronic technologies, yet their realization in chemically disordered systems has remained elusive.

Kai: First, who's behind it and why it matters.

Paper summary: Mira: Moving into the specifics of the paper, the authors detail how they confirmed that Cr3Al adopts a "fully A2-disordered configuration" where all atomic sites have mixed Cr and Al occupancy.

Kai: They then describe how magnetometry measurements revealed a "fully compensated ferrimagnetic (FCF) state," which is further supported by temperature-dependent neutron diffraction showing long-range ferrimagnetic order with a compensated magnetic moment.

Lev: That finding about the compensated magnetic moment is critical; running this on real hardware means we'd need to ensure that the system maintains this compensation even when subjected to thermal fluctuations, which is a tough challenge.

Mira: Electrically and thermally, they uncovered clear signatures of spin-gapless semiconductor (SGS) behavior, including weak temperature-dependent conductivity and very low Seebeck coefficients.

Kai: Their transport analysis fits the data using a two-carrier model with extracted energy gaps of "zero point nine two ± zero point zero seven meV for electrons and ninety-four ± four meV for holes," alongside an electron mobility calculated to be "∼one point eight cm2/(V·s)."

Lev: That calculated mobility figure tells us about the carrier scattering, and if that is indeed strong scattering associated with the chemical disorder, it confirms our hypothesis about how disorder influences transport in this material.

Mira: The theoretical validation involves spin-polarized density functional theory calculations on the A2-disordered phase, which reproduce these experimental features by showing a "vanishing spin-up band gap."

Kai: That vanishing gap is what unambiguously supports the SGS behavior driven by chemical disorder, and the model naturally yields an almost zero net moment through antiparallel Cr spin configurations across mixed sites.

Lev: If we were trying to design a quantum error correction system based on this, we’d have to consider how sensitive those spin configurations are to external fields or pressure, as the paper mentions SGS materials are highly sensitive to external factors ten eleven.

Mira: So, the main thrust of this research is establishing a consistent picture where the experimental signatures of SGS behavior align perfectly with electronic structure calculations on a fully disordered material.

Kai: It’s really about connecting what you measure experimentally—the transport and magnetic properties—to what you predict theoretically from first principles.

Conclusion: Mira: Looking at the conclusion of "Disorder mediated fully compensated ferrimagnetic spin-gapless semiconducting behaviour in Cr3Al Heusler alloy," the paper confirms Cr3Al as the first experimentally verified A2-disordered alloy exhibiting both fully compensated ferrimagnetism and SGS-like transport.

Kai: That means we have a material that combines robust magnetism with this specific kind of spin-selective transport, which is a big deal for spintronic applications.

Lev: From an error correction standpoint, the fact that it's disordertolerant in this way suggests a potentially stable platform for integrating spin functionality into larger circuits without immediately losing its magnetic or transport properties.

Mira: The implication is that chemical disorder, which we often think of as something detrimental to spin-polarized transport, can actually be a stabilizing force here under these specific conditions.

Kai: It positions Cr3Al as a distinctive and promising material for future spintronic technologies because it shows that these two seemingly opposite behaviors can coexist in one alloy structure.

Lev: I'm thinking about the next steps; if we could systematically tune this disorder through chemical substitution or strain engineering, we might be able to precisely modulate the band topology for more tailored spin polarization.

Mira: That systematic tuning is exactly where the future research direction lies, moving beyond just verifying the coexistence to actively controlling it for specific device architectures.

Kai: So, the big picture is that this work opens up a new platform in chemically disordered Heusler alloys for developing next-generation spintronic devices.

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