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The conduction type in (Zn,Sn,Mn)As2 thin films grown by molecular beam epitaxy (MBE) on InP substrates was found to be controllable from p-type to n-type as a function of Mn content. n-type (Zn,Sn,Mn)As2 thin films were obtained by Mn doping of more than approximately 11 cat.%. It is likely that Mn interstitials (MnI) incorporated by excess Mn doping are located at tetrahedral hollow spaces surrounded by Zn and Sn cation atoms and four As atoms, which are expected to act as donors in (Zn,Sn,Mn)As2, resulting in n-type conduction. The effect of annealing on the structural, electrical and magnetic properties of n-type (Zn,Sn,Mn)As2 thin films was investigated as functions of annealing temperature and time. It was revealed that even if the annealing temperature is considerably higher than the growth temperature of 320 °C, the magnetic properties of the thin films remain stable. This suggests that a MnI complex surrounded by Zn and Sn atoms is thermally stable during high-temperature annealing. The n-type (Zn,Sn,Mn)As2 thin films may be suitable for application as n-type spin-polarized injectors.

The structural, magnetic, and electrical properties of InMnAs thin films were investigated to elucidate their ferromagnetism for potential applications in InP-based spintronics and magneto-optical integrated circuits. The films were prepared on InP substrates by molecular beam epitaxy at growth temperatures of 220–280 °C without further annealing. Except for the 220 °C-grown sample, the films showed ferromagnetism at room temperature. We found that the room-temperature ferromagnetism was predominantly caused by the existence of hexagonal MnAs clusters embedded in a homogeneous InMnAs matrix (InMnAs:MnAs system). High-resolution transmission electron microscope images revealed that the MnAs nanoclusters formed either elongated or round structures in the InMnAs host matrix. The experimental results indicate that the mixed systems of hexagonal MnAs embedded in InMnAs may provide potential ferromagnetic building blocks for InP-based spintronics.

The crystalline structure and quality of ZnSnAs2:Mn films grown by molecular beam epitaxy (MBE) on InP substrates are two of the most important issues in preparing spintronic structures such as magnetic quantum wells and spin-based transistors. We conducted high-resolution X-ray diffraction (XRD) measurements to clarify the crystalline structure of ZnSnAs2:Mn thin films. The XRD measurements reveal with very high accuracy that the samples have a sphalerite structure with high epitaxial quality. These results, within the limits of measurement accuracy support the previous assumption that ZnSnAs2:Mn thin films are coherently clustered ferromagnetic semiconductors without breaking the continuity of the sphalerite structure, leading to ferromagnetism with a high Curie temperature close to that of zincblende MnAs.

The ferromagnetic transition in (Zn,Sn,Mn)As2 thin films is explained in terms of magnetic percolation in a Mn-As clustering network. We first studied the relationship between the spatial distribution of Mn-As clusters and the Curie temperature (TC). The local atomic structure was reconstructed from datasets of atomic positions in (Zn,Sn,Mn)As2 obtained by atom probe tomography (APT). To probe the local atomic structure and the magnetic properties of Mn-As clusters in ZnSnAs2 thin films, we investigated molecular beam epitaxially grown (Zn,Sn,Mn)As2 samples doped with 2.1 and 3.6 at. % Mn. Representative regions with a low and high Mn concentration were extracted from APT datasets. Mn-As clusters containing 2-36 Mn atoms were identified in regions of high Mn concentration. We also obtained a correlation between TC and Mn-As clustering that was consistent with not only the experimental results but also first-principles calculations using the mean-field approximation.The ferromagnetic transition in (Zn,Sn,Mn)As2 thin films is explained in terms of magnetic percolation in a Mn-As clustering network. We first studied the relationship between the spatial distribution of Mn-As clusters and the Curie temperature (TC). The local atomic structure was reconstructed from datasets of atomic positions in (Zn,Sn,Mn)As2 obtained by atom probe tomography (APT). To probe the local atomic structure and the magnetic properties of Mn-As clusters in ZnSnAs2 thin films, we investigated molecular beam epitaxially grown (Zn,Sn,Mn)As2 samples doped with 2.1 and 3.6 at. % Mn. Representative regions with a low and high Mn concentration were extracted from APT datasets. Mn-As clusters containing 2-36 Mn atoms were identified in regions of high Mn concentration. We also obtained a correlation between TC and Mn-As clustering that was consistent with not only the experimental results but also first-principles calculations using the mean-field approximation.

We have observed anomalous temperature dependence of magnetization of ZnSnAs 2 :Mn epitaxial thin films grown on InP(001) substrates compared with the values estimated by the mean-field theory using S = 5/2, as a function of temperature: The ZnSnAs 2 :Mn epitaxial thin films exhibits slightly increasing magnetization with rising temperature. From the first-principles calculation, when Mn substitutes for neighboring Zn sites in ZnSnAs 2 , MnZ n -MnZ n pairs result, which prefer antiferromagnetic (AFM) ordering. On the other hand, MnZ n -MnS n and MnS n -MnS n pairs can introduce both holes and spins, leading to ferromagnetic (FM) ordering. Thus, assuming that the magnetic property of ferromagnetic phase follows the mean-field theory, it can be explained by coexistence of FM and AFM phases.

We investigated the effect of film thickness on structural and magnetic properties of ZnSnAs 2 :Mn thin films. Samples with 80, 170 and 250 nm values of thickness were epitaxially grown on semi-insulating InP(001) substrates, followed by ZnSnAs 2 buffer layers using molecular beam epitaxy (MBE). The lattice constants and crystal structures were determined by X-ray diffraction (XRD). The reciprocal lattice mapping revealed that the 80-nm-thick sample could be completely lattice-matched with InP (001) substrates. Ferromagnetic hysteresis was clearly observed at 300 K for the 170 nm and 250 nm samples.

We investigated the influence of growth parameters on the film properties of multinary ZnSnAs 2 thin films with and without Mn doping grown by molecular beam epitaxy (MBE) on InP substrates. As growth parameters, the substrate temperature and the beam equivalent pressure (BEP) were varied. The most stoichiometric ZnSnAs 2 thin film was obtained when the substrate temperature was 340 °C. We found that the high-quality Mn-doped ZnSnAs 2 (ZnSnAs 2 :Mn) thin films can be realized by decreasing the beam flux of Zn source.

The relationship between Mn concentration and Curie temperature (TC) is studied for Mn-doped ZnSnAs2 ferromagnetic semiconductors, epitaxially grown on InP substrates by molecular beam epitaxy. In the ferromagnetic phase, Mn distributions in a (Zn,Mn,Sn)As2 thin film with 7.2 cation percent (cat. %) Mn are investigated using three-dimensional atom probe tomography. The results indicate an inhomogeneous distribution which spreads to a relatively high Mn concentration of 9.0 at. % (at. %). In the paramagnetic phase, it is found that the paramagnetic to ferromagnetic transition takes place sharply with a TC of 334 K when the Mn doping concentration increases to about 4 cat. % Mn, which corresponds to a magnetic percolation threshold for ferromagnetism in (Zn,Mn,Sn)As2. An effective Curie temperature ⟨TC⟩ is considered to bridge the Curie temperatures obtained experimentally to those calculated theoretically in inhomogeneous magnetic semiconductors. The behavior of magnetism in Mn-doped ZnSnAs2 can be explain...

The effects of cationic growth parameters of molecular beam epitaxy on the crystalline and magnetic properties of Mn-doped ZnSnAs2, (Zn,Sn,Mn)As2, thin films were investigated in order to control ferromagnetism at room temperature. The combination of cationic beam equivalent pressures of Zn, Sn, and Mn atoms was varied at an optimal substrate temperature of 320 °C. Clear hysteresis loops were observed for the samples at 300 K, indicating ferromagnetism at room temperature. We found that the change in Zn flux does not significantly affect the composition of (Zn,Sn,Mn)As2 thin films and ferromagnetic properties and that ferromagnetic properties definitely depend on the amounts of Mn and Sn fluxes. X-ray photoelectron spectroscopy analysis revealed that the sum of the amounts of Mn2+ and Mn4+, which may contribute to the ferromagnetism in (Zn,Sn,Mn)As2 thin films, was approximately 60–70% of the total Mn amount with respect to ferromagnetic (Zn,Sn,Mn)As2 samples. This result indicates that the ferromagnetic properties could be controlled in multilayered (Zn,Sn,Mn)As2 by changing the combination of Zn, Sn, and Mn fluxes.

The magnetization of (Zn,Sn,Mn)As2 thin films epitaxially grown on InP(001) substrates exhibited an anomalous temperature dependence, increasing slightly with temperature, compared with estimates based on the mean-field theory (MFT). Assuming that ferromagnetic (FM) and antiferromagnetic (AF) phases coexist at low temperature, these anomalous magnetic properties can be well explained by an AF-FM transition through a paramagnetic phase. The Neel temperature TN of the AF phase is estimated from the threshold of the difference curve between the experimental and theoretical data, assuming the magnetization of the FM phase, which follows the MFT. The estimated TN rapidly increases by ∼50 K in the range of Mn concentrations where the hexagonal MnAs (h-MnAs) phase precipitates. This can be explained by the superparamagnetic behavior of the precipitated h-MnAs nanoclusters, which possess a high blocking temperature.