Polarized Neutron Reflectivity Measurements Research Articles

Temperature- and magnetic field-induced magnetic structural changes in the Fe3Si/FeSi2 superlattice

Artificial lattices with semiconductor spacers are expected to exhibit changes in their magnetic structure owing to the control of their electronic states. The temperature (T) and magnetic-field (H ext) dependence of the in-plane magnetic structure of an [Fe3Si/FeSi2]20 superlattice with a nonmagnetic and semiconducting FeSi2 spacer layer is investigated using magnetization and polarized neutron reflectivity measurements. When H ext = 5 mT, nearly collinear antiferromagnetic (AF) structures are observed from 4 to 298 K. When H ext = 1 T, field-induced fan-like, noncollinear AF structures showing ferromagnetic components along H ext and transverse AF components are observed at low T.

Controllable Spin-Orbit Torque Induced by Interfacial Ion Absorption in Ta/CoFeB/MgO Multilayers with Canted Magnetizations.

Electrically generated spin-orbit torque (SOT) has emerged as a powerful pathway to control magnetization for spintronic applications including memory, logic, and neurocomputing. However, the requirement of external magnetic fields, together with the ultrahigh current density, is the main obstacle for practical SOT devices. In this paper, we report that the field-free SOT-driven magnetization switching can be successfully realized by interfacial ion absorption in perpendicular Ta/CoFeB/MgO multilayers. Besides, the tunable SOT efficiency exhibits a strong dependence on interfacial Ti insertion thicknesses. Polarized neutron reflection measurements demonstrate the existence of canted magnetization with Ti inserted, which leads to deterministic magnetization switching. In addition, interfacial characterization and first-principles calculations reveal that B absorption by the Ti layer is the main cause behind the enhanced interfacial transparency, which determines the tunable SOT efficiency. Our findings highlight an attractive scheme to a purely electric control spin configuration, enabling innovative designs for SOT-based spintronics via interfacial engineering.

Determining the Proximity Effect-Induced Magnetic Moment in Graphene by Polarized Neutron Reflectivity and X-ray Magnetic Circular Dichroism.

We report the magnitude of the induced magnetic moment in CVD-grown epitaxial and rotated-domain graphene in proximity with a ferromagnetic Ni film, using polarized neutron reflectivity (PNR) and X-ray magnetic circular dichroism (XMCD). The XMCD spectra at the C K-edge confirm the presence of a magnetic signal in the graphene layer, and the sum rules give a magnetic moment of up to ∼0.47 μB/C atom induced in the graphene layer. For a more precise estimation, we conducted PNR measurements. The PNR results indicate an induced magnetic moment of ∼0.41 μB/C atom at 10 K for epitaxial and rotated-domain graphene. Additional PNR measurements on graphene grown on a nonmagnetic Ni9Mo1 substrate, where no magnetic moment in graphene is measured, suggest that the origin of the induced magnetic moment is due to the opening of the graphene's Dirac cone as a result of the strong C pz-Ni 3d hybridization.

Magnetotransport and magnetic textures in Ho/FeCoGd/ β -W multilayers

The enhancement of interfacial Dzyaloshinskii-Moriya Interaction (DMI) in magnetic multilayers results in the stabilization of topological spin textures such as chiral domain walls and skyrmions. Here we report on the evaluation of interface-driven magnetic interactions in a uniquely designed multilayer where each magnetic layer of two antiferromagnetically coupled sublattices of $3d$ and $4f$ moments is sandwiched between the layers of \ensuremath{\beta}-tungsten and holmium whose spin Hall angles are large but opposite in sign. The atomic and magnetic periodicity of these multilayers is established by polarized neutron reflectivity measurements and the presence of a labyrinth domain spin texture of zero remanence with x-ray photoelectron microscopy. Measurements of the Hall resistivity $[{\ensuremath{\rho}}_{xy}(T,H)]$ together with static magnetization [$M$($T, H$)] over a broad range of temperature ($T$) and magnetic field ($H$) indicate impending compensation between $3d$ and $4f$ sublattices at $T>350\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. These multilayers are characterized by a small (0.04%) but positive magnetoresistance indicative of interface enhanced scattering, and a large (40 n\ensuremath{\Omega} m) and negative anomalous ${\ensuremath{\rho}}_{xy}(T,H)$ which results from a parallel alignment of $4f$ moments with the external magnetic field. No distinct scaling is seen between ${\ensuremath{\rho}}_{xy}(T,H), {\ensuremath{\rho}}_{xx}(T,H)$, and $M$($T, H$) at temperatures above 200 K where the magnetization develops out of plane anisotropy. The field scans of ${\ensuremath{\rho}}_{xy}$ at $T>200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ show a distinct cusp in the vicinity of magnetic saturation. These Hall data have been analyzed in the framework of a model where a distinct topological contribution to ${\ensuremath{\rho}}_{xy}$ rides over the anomalous Hall resistivities of the $3d$ and $4f$ magnetic sublattices. It is suggested that this apparent topological effect results from an interfacial DMI and dominates ${\ensuremath{\rho}}_{xy}(T,H)$ in the temperature regime where the $3d$ and $4f$ lattices are nearly compensated.

Local Spin Ice Order Induced Planar Hall Effect in Nd–Sn Artificial Honeycomb Lattice

AbstractGeometrically frustrated materials, such as spin ice or kagome lattice, are known to exhibit exotic Hall effect phenomena due to spin chirality. For the first time, Hall effect mechanism is explored in an artificial honeycomb spin ice of Nd–Sn element using Hall probe and polarized neutron reflectivity measurements. In an interesting observation, a strong enhancement in Hall signal at relatively higher temperature of T ∼ 20 K is detected. The effect is attributed to the planar Hall effect due to magnetic moment configuration in spin ice state in low field application. In the antiferromagnetic state of neodymium at low temperature, applied field induced coupling between atomic Nd moments and conduction electrons in underlying lattice causes distinct increment in Hall resistivity at very modest field of H ∼ 0.015 T. The experimental findings suggest the development of a new research vista to study the planar and the field induced Hall effects in artificial spin ice.

Helical magnetic structure and exchange bias across the compensation temperature of Gd/Co multilayers

Antiferromagnetic coupling between rare-earth (RE) and transition metals (TM) gives rise to various magnetic ground states in RE/TM heterostructures. Interface structure and morphology tend to play important roles in defining the magnetic properties of heterostructures of these materials. Using spin-dependent polarized neutron reflectivity (PNR), we found a distinct magnetic structure for RE/TM (Gd/Co) multilayers having different interface morphologies. Two Gd/Co multilayers, each consisting of eight bilayers of Gd and Co, were grown at different argon pressures to accomplish variation in the interface morphology. The Gd/Co multilayer, which is grown at a lower argon pressure, exhibits lower intermixing/interdiffusion at the interfaces and shows asymmetric magnetic hysteresis loops below the compensation temperature (Tcomp ∼ 140 K) and antisymmetric magnetoresistance at Tcomp. The other multilayer, grown at two different argon pressures for the top and bottom four bilayers, shows a double hysteresis loop with an exchange-bias-like shift to the field axis at temperatures above Tcomp (∼150 K). From PNR measurements across Tcomp, these behaviors were attributed to interface dependent magnetic helical structures. The PNR results indicate the formation of a twisted helical magnetic structure with planar 2π domain walls and the evolution of magnetic inhomogeneities below Tcomp. The interface dependent twisted helical magnetic structures and the development of highly correlated magnetic inhomogeneities may find applications in all-spin-based technologies.

Study of reactively sputtered nickel nitride thin films

Nickel nitride (Ni–N) thin film samples were deposited using reactive magnetron sputtering process utilizing the different partial flow of N2 (RN2). They were characterized using x-ray reflectivity (XRR), x-ray diffraction (XRD) and x-ray absorption near-edge spectroscopy (XANES) taken at N K-edge and Ni L-edges. From XRR measurements, we find that the deposition rate and the density of Ni–N films decrease due to successively progression in RN2, signifying that Ni–N alloys and compounds are forming both at Ni target surface and also within the thin film samples. The crystal structure obtained from XRD measurements suggest an evolution of different Ni–N compounds given by: Ni, Ni(N), Ni4N, Ni3N, and Ni2N with a gradual rise in RN2. XANES measurements further confirm these phases, in agreement with XRD results. Polarized neutron reflectivity measurements were performed to probe the magnetization, and it was found Ni–N thin films become non-magnetic even when N incorporation increases beyond few at.%. Overall growth behavior of Ni–N samples has been compared with that of rather well-known Fe–N and Co–N systems, yielding similarities and differences among them.

Charge carrier transport with low-temperature anomalies in engineered 4d/5d oxide superlattices of (Sr2IrO4)4/(Sr3Ru2O7)N

We report the tunable conducting behavior of a series of ${(\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4})}_{4}/{(\mathrm{S}{\mathrm{r}}_{3}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7})}_{N}$ ($N$ = 1, 2, and 4) atomic layer superlattices, in which phases of itinerant electrons, itinerant holes, localized electrons, and an anomalous charge region can be varied dependent on the period and the temperature. Specifically, for the $N$ = 4 superlattice, the electron-to-hole transition occurs at a temperature of 35 K, at which the sample behaves as an intrinsic insulator without either electrons or holes. Upon further reducing the temperature to below 16 K, the superlattice enters an anomalous phase region in which an abrupt zero-to-negative magnetoresistance transition and a Hall resistivity kink are observed at 1.3 and 2.1 T, respectively. Above these fields, polarized neutron reflectivity measurements revealed ferromagnetism confined in the $\mathrm{S}{\mathrm{r}}_{3}\mathrm{R}{\mathrm{u}}_{2}{\mathrm{O}}_{7}$ layers. Moreover, the $N$ = 2 superlattice exhibits a bump feature in the anomalous Hall resistivity near 1.3 T, which is similar to the previously reported topological Hall phenomenon in ultrathin $\mathrm{SrRu}{\mathrm{O}}_{3}$ heterostructures. We demonstrate that the layered $4d/5d$ oxide superlattice is a powerful platform in engineering exotic types of phases which have not been explored in their thin-film or bulk samples.

Enhanced anisotropy and study of magnetization reversal in Co/C60 bilayer thin film

The interface between the organic semiconductor (OSC)/ferromagnetic (FM) material can exhibit ferromagnetism due to their orbital hybridization. Charge/spin transfer may occur from the FM to OSC layer leading to the formation of “spinterface,” i.e., the interface exhibiting a finite magnetic moment. In this work, the magnetic properties of the Co/C60 bilayer thin film have been studied to probe the interface between the Co and C60 layer. Polarized neutron reflectivity (PNR) measurement indicates that the thickness and moment of the spinterface are ∼2 ± 0.18 nm and 0.8 ± 0.2 μB/cage, respectively. The comparison of the magnetization reversal between the Co/C60 bilayer and the parent single layer Co thin film reveals that spinterface modifies the domain microstructure. Further, the anisotropy of the bilayer system shows a significant enhancement (∼two times) in comparison to its single layer counterpart which is probably due to an additional interfacial anisotropy arising from the orbital hybridization at the Co/C60 interface.

Annealing driven positive and negative exchange bias in Fe–Cu–Pt heterostructures at room temperature

We report the annealing-induced exchange bias in Fe–Cu–Pt based heterostructures with Cu as an intermediate layer (Fe/Cu/Pt heterostructure) and as a capping layer (Fe/Pt/Cu heterostructure). The exchange bias (shift in the hysteresis loop along the field axis) observed at room temperature (300 K) is found to be dependent on the annealing temperature. We obtained positive exchange bias of ∼ +120 Oe on annealing both the heterostructures at 400 °C, while on annealing these heterostructures at 500 and 600 °C a negative exchange bias of ∼ −100 Oe was observed. X-ray and polarized neutron reflectivity measurements show the evolution of the depth-dependent structure and magnetic properties of the heterostructures on annealing at different temperatures and revealed the coexistence of soft and hard (alloy) magnetic phases across the thickness of the films. Rapid and long-range interdiffusion at interfaces on annealing the systems at a temperature 〉 400 °C resulted into the formation of a ternary alloy phase. The observation of annealing-induced positive and negative exchange bias effect is dependent on the applied field and majority of the magnetic phase (hard/soft), present in the system. This annealing dependent coupling could give rise to more advanced applications of hard/soft ferromagnetic heterostructures.

Dynamics of reactive sputtering affecting phase formation of Co–N thin films

Target poisoning is one of the major drawbacks of reactive sputtering (RS) affecting the stoichiometry of a compound film depositing onto a substrate. The dynamics of RS has been understood in terms of the well-known ‘Berg’s Model’ (Berg et al. in Thin Solid Films 565:186, 2014; Berg and Nyberg in Thin Solid Films 476(2):215, 2005) which demonstrates that by reducing the size of a sputter target, the drawbacks of RS can be minimized. In the present work, we compare the evolution of cobalt–nitride (Co–N) phases in an RS process from two different sized magnetron sources having diameter of 1 and 3 in. Samples were studied for their long-range ordering and local structure using X-ray diffraction and X-ray absorption spectroscopy. Quantification of N at.% was carried out using secondary ion mass spectroscopy. Polarized neutron reflectivity and bulk magnetization measurements were carried out to study the magnetic properties of Co–N thin film samples. We found that the N incorporation in Co–N films can be accelerated utilizing the smaller source. In addition, by reducing the target size from 3 to 1 in., the range of metallic state can be extended. The $${\mathrm {Co}}_{4}{\mathrm {N}}$$ phase emerging from the metallic state of the smaller target has a lattice parameter more closer to its theoretical value. An insight has been presented on the RS process and it can be readily seen from this work that the poisoning of the target can be minimized for the growth of the $${\mathrm {Co}}_{4}{\mathrm {N}}$$ film from the smaller target and can be understood in accordance with the available theoretical models.

Synthesis, structure and magnetization of Co4N thin films

Abstract We reviewed magnetic tetra metal nitrides – Fe 4 N and Co 4 N for their structure, magnetization and the thermodynamics of phase formation. Opposed to Fe 4 N , the formation of a stoichiometric Co 4 N turns out to be extremely difficult. A review of the literature of Co 4 N compound suggest that the experimental lattice parameter (LP) was always found to be smaller than the theoretical predicted value. It can also be seen that as the substrate temperature ( T s ) increases, the LP of Co 4 N film decreases. In this work, we deposited Co 4 N films using molecular beam epitaxy (MBE), direct current magnetron sputtering (dcMS) and high power impulse MS (HiPIMS). Films were characterized using X-ray diffraction, X-ray reflectivity and atomic force microscopy. It was found that at high T s , N out-diffusion significantly affects the growth of Co 4 N phase. We found that the MBE deposited films did not show any signature of Co 4 N phase when T s 703 K but at T s = 703 K , the phase formed can be assigned to fcc Co rather than Co 4 N . On the other hand, the dcMS and HiPIMS grown films clearly show the presence of Co 4 N phase even at T s = 300 K . Detailed analysis of Co 4 N films grown using dcMS and HiPIMS reveals that HiPIMS grown films are single phase and have a denser microstructure. The density of HiPIMS deposited film was also found to be close to the theoretical value. Magneto optical Kerr effect and polarized neutron reflectivity measurements were carried out to study magnetic properties. Differences in the magnetic moment and magnetic anisotropy were correlated with structural parameters. Obtained results are presented and discussed in terms of involved thin film growth mechanism.

Probing the Transfer of the Exchange Bias Effect by Polarized Neutron Reflectometry

The magnetic reversal behavior of a ferromagnet (FM) coupled through an FeMn antiferromagnet (AF) to a pinned ferromagnet has been investigated by polarized neutron reflectivity measurements. With FeMn as the AF layer it is found that there exists 90° interlayer coupling through this layer and that this plays a key role in the transfer of the exchange bias (EB) effect from the FM/AF interface to the AF/pinned-FM interface. Combined with Monte Carlo simulations, we demonstrate that the competition between the interlayer coupling and the anisotropy of the AF layer results in a control of the EB effect which has potential for device applications.

Effect of magnetic fullerene on magnetization reversal created at the Fe/C60 interface

Probing the hybridized magnetic interface between organic semiconductor (OSC) and ferromagnetic (FM) layers has drawn significant attention in recent years because of their potential in spintronic applications. Recent studies demonstrate various aspects of organic spintronics such as magnetoresistance, induced interface moment etc. However, not much work has been performed to investigate the implications of such OSC/FM interfaces on the magnetization reversal and domain structure which are the utmost requirements for any applications. Here, we show that non-magnetic Fullerene can obtain non-negligible magnetic moment at the interface of Fe(15 nm)/C60(40 nm) bilayer. This leads to substantial effect on both the magnetic domain structure as well as the magnetization reversal when compared to a single layer of Fe(15 nm). This is corroborated by the polarized neutron reflectivity (PNR) data which indicates presence of hybridization at the interface by the reduction of magnetic moment in Fe. Afterwards, upto 1.9 nm of C60 near the interface exhibits magnetic moment. From the PNR measurements it was found that the magnetic C60 layer prefers to be aligned anti-parallel with the Fe layer at the remanant state. The later observation has been confirmed by domain imaging via magneto-optic Kerr microscopy.

Development of high-polarization Fe/Ge neutron polarizing supermirror: Possibility of fine-tuning of scattering length density in ion beam sputtering

The multilayer structure of Fe/Si and Fe/Ge systems fabricated by ion beam sputtering (IBS) was investigated using X-ray and polarized neutron reflectivity measurements and scanning transmission electron microscopy with energy-dispersive X-ray analysis. The obtained result revealed that the incorporation of sputtering gas particles (Ar) in the Ge layer gives rise to a marked reduction in the neutron scattering length density (SLD) and contributes to the SLD contrast between the Fe and Ge layers almost vanishing for spin-down neutrons. Bundesmann et al. (2015) have shown that the implantation of primary Ar ions backscattered at the target is responsible for the incorporation of Ar particles and that the fraction increases with increasing ion incidence angle and increasing polar emission angle. This leads to a possibility of fine-tuning of the SLD for the IBS, which is required to realize a high polarization efficiency of a neutron polarizing supermirror. Fe/Ge polarizing supermirror with m=5 fabricated under the same condition showed a spin-up reflectivity of 0.70 at the critical momentum transfer. The polarization was higher than 0.985 for the qz range where the correction for the polarization inefficiencies of the beamline works properly. The result of the polarized neutron reflectivity measurement suggests that the “magnetically-dead” layers formed at both sides of the Fe layer, together with the SLD contrast, play a critical role in determining the polarization performance of a polarizing supermirror.

Atomic-scale engineering of ferroelectric-ferromagnetic interfaces of epitaxial perovskite films for functional properties

Besides epitaxial mismatch that can be accommodated by lattice distortions and/or octahedral rotations, ferroelectric-ferromagnetic interfaces are affected by symmetry mismatch and subsequent magnetic ordering. Here, we have investigated La0.67 Sr0.33 MnO3 (LSMO) samples with varying underlying unit cells (uc) of BaTiO3 (BTO) layer on (001) and (110) oriented substrates in order to elucidate the role of symmetry mismatch. Lattice mismatch for 3 uc of BTO and symmetry mismatch for 10 uc of BTO, both associated with local MnO6 octahedral distortions of the (001) LSMO within the first few uc, are revealed by scanning transmission electron microscopy. Interestingly, we find exchange bias along the in-plane [110]/[100] directions only for the (001) oriented samples. Polarized neutron reflectivity measurements confirm the existence of a layer with zero net moment only within (001) oriented samples. First principle density functional calculations show that even though the bulk ground state of LSMO is ferromagnetic, a large lattice constant together with an excess of La can stabilize an antiferromagnetic LaMnO3-type phase at the interface region and explain the experimentally observed exchange bias. Atomic scale tuning of MnO6 octahedra can thus be made possible via symmetry mismatch at heteroepitaxial interfaces. This aspect can act as a vital parameter for structure-driven control of physical properties.

A versatile UHV transport and measurement chamber for neutron reflectometry under UHV conditions.

We report on a versatile mini ultra-high vacuum (UHV) chamber which is designed to be used on the MAgnetic Reflectometer with high Incident Angle of the Jülich Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum in Garching, Germany. Samples are prepared in the adjacent thin film laboratory by molecular beam epitaxy and moved into the compact chamber for transfer without exposure to ambient air. The chamber is based on DN 40 CF flanges and equipped with sapphire view ports, a small getter pump, and a wobble stick, which serves also as sample holder. Here, we present polarized neutron reflectivity measurements which have been performed on Co thin films at room temperature in UHV and in ambient air in a magnetic field of 200 mT and in the Q-range of 0.18 Å-1. The results confirm that the Co film is not contaminated during the polarized neutron reflectivity measurement. Herewith it is demonstrated that the mini UHV transport chamber also works as a measurement chamber which opens new possibilities for polarized neutron measurements under UHV conditions.

Simultaneous measurement of volume and grain boundary diffusivity separately in Fe thin film with stable nanostructure using polarized neutron reflectivity

Polarized neutron reflectivity (PNR) measurements have been used for simultaneous measurement of volume and grain boundary diffusivity separately in stable nanocrystalline Fe thin film at very low homologous temperature (0.2 Tm < T < 0.3 Tm). PNR measurements were done on Si (substrate)/Fe (150 nm)/[57Fe (3 nm)/natFe (9 nm)]x10 thin film system with periodic 57Fe isotope modulation. PNR from as deposited film shows strong Bragg peaks due to neutron scattering length contrast between 57Fe and natFe layers. Atomic Diffusivity was measured from decrease in the intensity of the Bragg peak due to interdiffusion of 57Fe and natFe layers after annealing the film at three different temperatures 418 K, 483 K and 548 K, respectively for different time intervals starting from 30 min to several hours. The change in the nanostructure of the film after annealing is characterized using grazing incidence x-ray diffraction. No appreciable grain growth within error bar is observed in the film after annealing indicating that the diffusion measurements were done in stable nanostructure. It is observed that the grain boundary diffusivity is two orders of magnitude higher than the volume diffusivity. However, the mechanism of atomic diffusion is similar in both grain and grain boundary.

Ferromagnetism and spin-dependent transport inn-type Mn-doped bismuth telluride thin films

We describe a detailed study of the structural, magnetic, and magneto-transport properties of single-crystal, n-type, Mn-doped Bi2Te3 thin films grown by molecular beam epitaxy. With increasing Mn concentration, the crystal structure changes from the tetradymite structure of the Bi2Te3 parent crystal at low Mn concentrations towards a BiTe phase in the (Bi2Te3)m(Bi2)n homologous series. Magnetization measurements reveal the onset of ferromagnetism with a Curie temperature in the range 13.8 K - 17 K in films with 2 % - 10 % Mn concentration. Magnetization hysteresis loops reveal that the magnetic easy axis is along the c-axis of the crystal (perpendicular to the plane). Polarized neutron reflectivity measurements of a 68 nm-thick sample show that the magnetization is uniform through the film. The presence of ferromagnetism is also manifest in a strong anomalous Hall effect and a hysteretic magnetoresistance arising from domain wall scattering. Ordinary Hall effect measurements show that the carrier density is n-type, increases with Mn doping, and is high enough (> 2.8 x 10^{13} cm^{-2}) to place the chemical potential in the conduction band. Thus, the observed ferromagnetism is likely associated with both bulk and surface states. Surprisingly, the Curie temperature does not show any clear dependence on the carrier density but does increase with Mn concentration. Our results suggest that the ferromagnetism probed in these Mn-doped Bi2Te3 films is not mediated by carriers in the conduction band or in an impurity band.

Ferromagnetism in Bi2Se3:Mn epitaxial layers

The magnetism in \ensuremath{\sim}1 at$%$ Mn-doped nanometric Bi${}_{2}$Se${}_{3}$ epitaxial layers has been studied by ferromagnetic resonance (FMR), magnetometry, and polarized neutron reflectivity (PNR) measurements. The FMR results reveal the formation of an intrinsic homogeneous FM bulk phase, as confirmed by the PNR measurements. Its critical temperature is low: ${T}_{c}$ \ensuremath{\approx} 6 K; no surface magnetic phase is detected above this temperature. The FMR measurements at $T$ $=$ 4.2 K show a single uniform mode spectrum with a strong uniaxial in-plane/out-of-plane symmetry. The uniaxial anisotropy field at $T$ $=$ 4 K is ${H}_{a}$ \ensuremath{\sim} \ensuremath{-}2500 Oe, corresponding to a uniaxial anisotropy constant of \ensuremath{-}9 \ifmmode\times\else\texttimes\fi{} 10${}^{3}$ erg/cm${}^{3}$. The easy axis of magnetization is oriented in the film plane for temperatures between 4 K and ${T}_{c}$. Conduction electron-mediated FM in this (very) diluted magnetic semiconductor is considered as the most probable origin of the FM phase formation.