A microscopic mystery at the heart of next-generation spintronic materials has come into sharper focus. Using muon spin relaxation and rotation (µSR), an international research team has mapped how magnetic order emerges in bulk Li(Zn,Mn)As, a diluted ferromagnetic semiconductor designed to overcome several limitations of the widely studied material (Ga,Mn)As. The study reveals that long-range ferromagnetism becomes fully homogeneous at approximately 5% manganese substitution, while lower manganese concentrations produce a patchwork of static magnetic regions and fluctuating spins. The results offer a rare atomic-scale view of how magnetism develops in a disordered semiconductor and challenge assumptions about the dynamics of its transition into the ferromagnetic state.
Diluted ferromagnetic semiconductors are materials in which a small fraction of the atoms in a semiconductor lattice is replaced by magnetic ions. Their unusual combination of electrical conductivity and controllable magnetism makes them attractive for spintronics, an emerging technology that aims to use electron spin as well as electric charge to process and store information. The benchmark system, (Ga,Mn)As, has helped establish the field, but it must generally be produced as a thin film using molecular beam epitaxy. It also has limited air stability, and the same chemical substitutions that introduce magnetic manganese ions can influence the material’s charge-carrier concentration. These linked effects make it difficult to determine which microscopic mechanisms are responsible for its magnetic behavior.
Li(Zn,Mn)As offers a different experimental platform. In this cubic F-43m semiconductor, manganese ions with a valence of Mn²⁺ replace Zn²⁺ ions, introducing localized magnetic moments without directly changing the charge balance. Electrical carriers can then be adjusted independently through excess lithium. This separation of spin doping from charge doping gives researchers greater control over the ingredients needed for ferromagnetism. Unlike (Ga,Mn)As, Li(Zn,Mn)As can also be prepared as a chemically stable bulk material, making it suitable for measurements that are difficult or impossible in fragile thin films. Earlier experiments showed that both manganese spins and charge carriers are needed to produce ferromagnetic order, but the way that order evolves through the crystal had remained uncertain.
To investigate the process, the team examined four compositions of Li₁₊ᵧ(Zn₁₋ₓMnₓ)As, ranging from an undoped paramagnetic reference sample to materials with higher manganese concentrations. The experiments were performed at TRIUMF in Canada using zero-field, weak-transverse-field and longitudinal-field µSR. In µSR, positively charged muons are implanted into a material, where their spins act as extremely sensitive local magnetic probes. As the muons decay, the direction of their emitted positrons records how their spins have changed. Static internal magnetic fields cause characteristic depolarization patterns, while fluctuating fields generate relaxation that reflects the timescale of local spin dynamics. Together, these signals can distinguish magnetic regions that appear identical to conventional bulk measurements.
The researchers also developed a global analysis method combining Lorentzian Kubo-Toyabe functions with stretched-exponential relaxation models. This approach allowed them to track both the static magnetic volume fraction and the dynamic spin component over broad temperature and field ranges. That distinction was crucial. At a manganese concentration of 3%, only about 56% of the sample volume developed static ferromagnetic order at low temperature, while the remaining regions retained dynamic, paramagnetic behavior. The material was therefore not simply a weak ferromagnet; it contained magnetically ordered domains embedded in a fluctuating background. When the manganese concentration reached 5%, however, the entire sample volume became statically ordered at 1.8 kelvin, indicating that the magnetic network had crossed a percolation threshold.
Percolation describes the point at which individually separated magnetic regions connect to form a continuous, system-spanning network. In diluted magnetic semiconductors, one possible route to this connectivity involves bound magnetic polarons. These are regions in which a charge carrier locally aligns nearby magnetic moments, creating a magnetically polarized cloud. As the concentration of carriers and magnetic ions increases, such clouds can overlap, allowing long-range ferromagnetic order to spread through the material. The experimentally identified threshold near 5% manganese, under conditions of 10% excess lithium, provides a quantitative benchmark for testing this picture. It also shows that the onset of ferromagnetism is not determined solely by the presence of magnetic ions, but by whether those ions can form a connected magnetic structure throughout the sample.
Longitudinal-field measurements revealed an additional distinction between the compositions. A magnetic field applied parallel to the initial muon-spin direction can suppress relaxation caused by weak, quasi-static local fields, a phenomenon known as decoupling. In the 5% manganese sample, the low-temperature signal was consistent with predominantly static local moments, supporting the picture of a homogeneous ferromagnetic ground state. The lower-manganese sample behaved differently: static ordered regions coexisted with fluctuating spin environments. This microscopic separation helps explain why some diluted ferromagnetic semiconductors deviate from simple relationships connecting the static relaxation rate and Curie temperature. It also provides a physical basis for comparing apparently different materials, including (Ga,Mn)As, Li(Zn,Mn)P and Na(Zn,Mn)Sb, within a common framework.
The most surprising result appeared near the Curie temperature, the point at which the material changes from a ferromagnet to a paramagnet. In many conventional magnetic systems, spins become increasingly slow and correlated as the transition approaches, producing a pronounced peak in the longitudinal-field relaxation rate, or 1/T₁. Such critical slowing down is often regarded as a signature of collective magnetic fluctuations near a continuous phase transition. Li(Zn,Mn)As did not show this expected sharp response. Both the homogeneous and phase-separated compositions displayed only mild relaxation anomalies around their Curie temperatures. The absence of strong critical dynamics suggests that disorder, dilute magnetic connectivity or bound magnetic polaron physics may be suppressing the fluctuations predicted by standard three-dimensional disordered Heisenberg models. At the same time, the observations do not completely match existing theoretical descriptions, leaving the precise nature of the transition unresolved.
The findings give researchers a new way to evaluate magnetic homogeneity in bulk diluted ferromagnetic semiconductors. Rather than relying only on average magnetization, µSR can determine how much of a sample is magnetically ordered and whether apparently ordered regions contain rapidly fluctuating spins. The work also establishes what the team describes as a full-spectrum quantitative fitting protocol for weak-transverse-field µSR studies of these materials. Future experiments will need to combine this local magnetic information with high-resolution transport, heat-capacity and magnetization-hysteresis measurements. More closely spaced manganese concentrations could refine the percolation threshold, while longitudinal-field µSR on higher-temperature materials such as BaZn₂As₂-family compounds could reveal whether suppressed critical dynamics are a general feature of bulk diluted ferromagnetic semiconductors. Ultimately, the ability to control homogeneous and phase-separated magnetic states could support new spintronic devices in which magnetic order is tuned by composition, pressure or electric fields.
Subject of Research: Magnetic ground states, ferromagnetic percolation, phase separation and critical spin dynamics in the diluted ferromagnetic semiconductor Li(Zn,Mn)As.
Article Title: Magnetic ground state, evolution, and critical dynamics in the new generation diluted ferromagnetic semiconductors Li(Zn,Mn)As: a μSR perspective
News Publication Date: 17 July 2026
Web References: https://doi.org/10.1088/2752-5724/ae84ef
References: Guoqiang Zhao, Zheng Deng, Baosen Min, Timothy Ziman, Gang Su, Bo Gu, Changqing Jin and Yasutomo J. Uemura. “Magnetic ground state, evolution, and critical dynamics in the new generation diluted ferromagnetic semiconductors Li(Zn,Mn)As: a μSR perspective.” Materials Futures, 2026, 5(4): 045201. DOI: 10.1088/2752-5724/ae84ef
Image Credits: Guoqiang Zhao, Zheng Deng, Baosen Min, Timothy Ziman, Gang Su, Bo Gu, Changqing Jin and Yasutomo J. Uemura
Keywords
Li(Zn,Mn)As, diluted ferromagnetic semiconductors, spintronics, muon spin relaxation, μSR, ferromagnetism, magnetic percolation, bound magnetic polarons, critical spin dynamics, magnetic semiconductors
Tags: atomic-scale magnetic order mappingbulk Li(Znchallenges in (Gadisordered magnetic semiconductorslimitations of thinlong-range ferromagnetism in diluted semiconductorsmagnetic ion substitution effects in spintronicsmagnetic phase transition in semiconductorsmicroscopic magnetism in semiconductorsMn)As fabricationMn)As magnetic propertiesmuon spin relaxation in magnetic materialsspintronic applications of diluted ferromagnetic semiconductorsspintronic materials
