Ferromagnetic MnBi4Te7 obtained with low concentration Sb doping: A promising platform for exploring topological quantum states
Y. D. Guan, C. H. Yan, S. H. Lee, X. Gui, W. Ning, J. L. Ning, Y. L. Zhu, M. Kothakonda, C. Q. Xu, X. L. Ke, J. W. Sun, W. W. Xie, S. L. Yang, Z. Q. Mao
备注：
37 Pages, 7 Figures and 2 Tables. Supplementary Materials is included
The tuning of magnetic phase, chemical potential, and structure is crucial to observe diverse exotic topological quantum states in $MnBi_2Te_4(Bi_2Te_3)_m$ (m = 0, 1, 2, & 3). Here we show a ferromagnetic (FM) phase with a chiral crystal structure in $Mn(Bi_{1-x}Sb_x)_4Te_7$, obtained via tuning the growth conditions and Sb concentration. Unlike previously reported $Mn(Bi_{1-x}Sb_x)_4Te_7$, which exhibits FM transitions only at high Sb doping levels, our samples show FM transitions ($T_C$ = 13.5 K) at 15%-27% doping levels. Furthermore, our single crystal x-ray diffraction structure refinements find Sb doping leads to a chiral structure with the space group of P3, contrasted with the centrosymmetric P-3m1 crystal structure of the parent compound $MnBi_4Te_7$. Through ARPES measurements, we also demonstrated that the non-trivial band topology is preserved in the Sb-doped FM samples. Given that the non-trivial band topology of this system remains robust for low Sb doping levels, our success in making FM $Mn(Bi_{1-x}Sb_x)_4Te_7$ with $x$ = 0.15, 0.175, 0.2 & 0.27 paves the way for realizing the predicted topological quantum states such as axion insulator and Weyl semimetals. Additionally, we also observed magnetic glassy behavior in both antiferromagnetic $MnBi_4Te_7$ and FM $Mn(Bi_{1-x}Sb_x)_4Te_7$ samples, which we believe originates from cluster spin glass phases coexisting with long-range AFM/FM orders. We have also discussed how the antisite Mn ions impact the interlayer magnetic coupling and how FM interlayer coupling is stabilized in this system.
We have found high ferromagnetic transition temperature in Mn delta-doped GaAs-based heterostructures grown on GaAs(001) substrates by molecular beam epitaxy. A 0.3 ML Mn d-doped GaAs samples showed high resistivity at low temperature and did not show a ferromagnetic behavior. However, in a selectively doped heterostructure (Mn delta-doped GaAs / Be-doped AlGaAs), where holes were supplied from the Be-doped AlGaAs layer, clear ferromagnetic order was observed. The ferromagnetic transition temperature of the selectively doped heterostructure was as high as 172K with suitable low-temperature (LT…
We present a study of p-type doping of CdTe and Cd$_{1-x}$Mn$_x$Te quantum wells from surface states. We show that this method is as efficient as usual modulation doping with nitrogen acceptors, and leads to hole densities exceeding $2 \times 10^{11}$ cm$^{-2}$. Surface doping was successfully applied to obtain carrier-induced ferromagnetism in a Cd$_{1-x}$Mn$_x$Te quantum well. The observed temperature dependence of photoluminescence spectra, and the critical temperature, correspond well to those previously reported for ferromagnetic quantum wells doped with nitrogen.
Recently the discovery of magnetic order in two-dimensional monolayer chromium trihalides opens the new research field in two-dimensional materials. We use first-principles calculations to systematically examine the doping effect of chalcogen on CrBr3. In the case of S-doping, four stable configurations, Cr2Br5S, Cr2Br4S2-A, Cr2Br4S2-B and Cr2Br3S3-A, are predicted to be ferromagnetic semiconductors. It is found that the new bands appearing in the original bandgap are made up of S-p and Cr-d-egorbits, lead to the obvious reduce of bandgap and the enhanced optical absorption in the visible rang…
Based on experimental observations in A{x}MO{2} (A = Na, Li; M = Co, Ni), a model for suppression of magnetic frustration by electron doping in a nearest-neighbour antiferromagnetic triangular lattice is presented. It is found that frustration can be quantified, as determined by geometry and bond-counting, and its magnitude is a non-monotonic function of $x$. A mean-field calculation provides temperature-dependent magnetization, spin-entropy and heat capacity. Low-doping (x = 0.25, 0.33) results in a highly frustrated regime. A{0.5}MO{2} has strongest order and no frustration, while high dopin…
We have investigated the transport and magnetic properties of group-IV ferromagnetic semiconductor Ge1-xFex films (x = 1.0 and 2.3 %) with and without boron doping grown by molecular beam epitaxy (MBE). In order to accurately measure the transport properties of 100-nm-thick Ge1-xFex films, (001)-oriented silicon-on-insulator (SOI) wafers with an ultra-thin Si body layer (~5 nm) were used as substrates. Owing to the low Fe content, the hole concentration and mobility in the Ge1-xFex films were exactly estimated by Hall measurements because the anomalous Hall effect in these films was found to b…
The magnetization compensation phenomenon is observed for Sm1-xNdxScGe at x = 0.09 at a temperature near 90 K in a small applied magnetic field, which establishes the spin surplus status of magnetic moment of Sm in the host matrix. We also noted that the sample profiles in QD SQUID magnetometer become asymmetric in some situations indicating significant contributions from multiple moments higher than the dipole moment. We have successfully accounted for them using a fitting procedure involving the higher order magnetic moments.
The effect of modulation doping by Be on the ferromagnetic properties of Ga(1-x)Mn(x)As is investigated in Ga(1-x)Mn(x)As/Ga(1-y)Al(y)As heterojunctions and quantum wells. Introducing Be acceptors into the Ga(1-y)Al(y)As barriers leads to an increase of the Curie temperature T_C of Ga(1-x)Mn(x)As, from 70 K in undoped structures to over 100 K with the modulation doping. This increase is qualitatively consistent with a multi-band mean field theory simulation of carrier-mediated ferromagnetism. An important feature is that the increase of T_C occurs only in those structures where the modulation …
We present a theoretical study of (Ga,Mn)(As,C) diluted magnetic semiconductors with high C acceptor density that combines insights from phenomenological model and microscopic approaches. A tight-binding coherent potential approximation is used to describe the electronic structure in the presence of Mn$_{\rm Ga}$ and C$_{\rm As}$ impurities. We find only a small effect of C on the distribution and coherence of electronic states close to the top of the valence band and on the coupling between Mn moments, even at doping levels of several per cent. These results justify applying the model of ferr…
Experimentally Cr doping in the rutile phase of VO$_2$ is found to stabilize a charge ordered ferromagnetic insulating state in the doping range of 10\% to 20\%. In this work, we investigated its origin at 12.5\% Cr doping using a combination of ab-initio electronic structure calculations as well as microscopic modeling. Our calculations are found to reproduce the ferromagnetic insulating state as well as a charge ordering at the V and Cr sites. The mapping of the ab-initio band structure onto a tight-binding Hamiltonian allows one to calculate the energy gain from different exchange pathways.…
(La1-xSrx)(Zn1-yMny)AsO is a two dimensional diluted ferromagnetic semiconductor that has the advantage of decoupled charge and spin doping. The substitution of Sr2+ for La3+ and Mn2+ for Zn2+ into the parent semiconductor LaZnAsO introduces hole carriers and spins, respectively. This advantage enables us to investigate the influence of carrier doping on the ferromagnetic ordered state through the control of Sr concentrations in (La1-xSrx)(Zn0.9Mn0.1)AsO. 10 % Sr doping results in a ferromagnetic ordering below TC ~ 30 K. Increasing Sr concentration up to 30 % heavily suppresses the Curie temp…
We have performed x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) studies of the diluted ferromagnetic semiconductor Zn$_{1-\textit{x}}$Cr$_\textit{x}$Te doped with iodine (I) or nitrogen (N), corresponding to electron or hole doping, respectively. From the shape of the Cr $2p$ absorption peak in the XAS spectra, it was concluded that Cr ions in the undoped, I-doped and lightly N-doped samples are divalent (Cr$^{2+}$), while Cr$^{2+}$ and trivalent (Cr$^{3+}$) coexist in the heavily N-doped sample. This result indicates that the doped nitrogen atoms act as acce…
The study of the ordered oxygen deficient perovskite EuBaCo2-xNixO5.50 shows that the doping of cobalt sites by nickel induces a strong ferromagnetic component at low temperature in the antiferromagnetic matrix of EuBaCo2O5.50. This system exhibits indeed phase separation, i.e. consists of ferromagnetic domains embedded in the antiferromagnetic matrix of EuBaCo2O5.50. Besides, a magnetic transition is observed for the first time at 40K in the undoped and nickel doped phases, which can be attributed to the ferromagnetic ordering of the Eu3+ moments below this temperature. Moreover sharp ultra m…
The structural, optical and magnetic properties of the Zn1-xMnxO (0 < x < 0.05) thin films synthesized by sol-gel technique have been analyzed in the light of modification of the electronic structure and disorder developed in the samples due to Mn doping. The films are of single phase in nature and no formation of any secondary phase has been detected from structural analysis. Absence of magnetic impurity phase in these films confirmed from morphological study also. Increasing tendency of lattice parameters and unit cell volume has been observed with increasing Mn doping concentration. The inc…
We present in this paper the changes in the room temperature magnetic property of ZnO on Mn doping prepared using solvo-thermal process. The zero field cooled (ZFC) and field cooled (FC) magnetisation of undoped ZnO showed bifurcation and magnetic hysteresis at room temperature. Upon Mn doping the magnetic hysteresis at room temperature and the bifurcation in ZFC-FC magnetization vanishes. The results seem to indicate that undoped ZnO is ferromagnetic while on the other hand the Mn doped ZnO is not a ferromagnetic system. We observe that on addition of Mn atoms the system shows antiferromagnet…
The structure, electronic, and magnetic properties of the Mo-doped perovskite La0.7Ca0.3Mn1-xMoxO3 (x < 0.1) have been studied. A significant increase in resistivity and lattice parameters were observed with Mo doping. A marginal decrease in the Curie temperature Tc and the associated metal-insulator transition Tp were observed. Magnetization data reveal that long-range ferromagnetic ordering persists in all samples studied and the saturation moment decreases linearly as x increases. Enhancement in magnetoresistance at near Tc in the Mo-doped compounds with an optimum doping value x = 0.05 was…
We show that doped cubic iron pyrite, which is a diamagnetic semiconductor, becomes ferromagnetic when $p$-type doped. We furthermore find that this material can exhibit high spin polarization both for tunneling and transport devices. These results are based on first principles electronic structure and transport calculations. This illustrates the use of $p$-type doping without magnetic impurities as a strategy for obtaining ferromagnetic semiconducting behavior, with implications for spintronic applications that require both magnetic ordering and good mobility. This is a combination that has b…
Ferromagnetic semiconductors promise the extension of metal-based spintronics into a material system that combines widely tunable electronic, optical, and magnetic properties. Here, we take steps towards realizing that promise by achieving independent control of electronic doping in the ferromagnetic semiconductor (Ga,Mn)As. Samples are comprised of superlattices of 0.5 monolayer (ML) MnAs alternating with 20 ML GaAs and are grown by low temperature (230 C) atomic layer epitaxy (ALE). This allows for the reduction of excess As incorporation and hence the number of charge-compensating As-relate…
The seeking of room temperature ferromagnetic semiconductors, which take advantages of both the charge and spin degrees of freedom of electrons to realize a variety of functionalities in devices integrated with electronic, optical, and magnetic storage properties, has been a long-term goal of scientists and engineers. Here, by using the spin-polarized density functional theory calculations, we predict a new series of high temperature ferromagnetic semiconductors based on the melilite-type oxysulfide Sr$_2$MnGe$_2$S$_6$O through hole (K) and electron (La) doping. Due to the lack of strong antif…
A two-dimensional scandium monochloride sheet was investigated by using density functional theory. It could be exfoliated from a known bulk material with a cleavage energy slightly lower than that of graphene. The sheet has a ferromagnetic ground state with a Curie temperature of 100 K. Moreover, the sheet becomes a half-metal under hole doping. The Curie temperature increases to 250 K with the doping amount of 0.4 per primitive cell, which is close to the ice point. The two-dimensional scandium monochloride sheet should be a good candidate for two-dimensional spintronics.
Ferromagnetic resonance (FMR) is used to study magnetic anisotropy of GaMnAs in a series of Ga$_{1 - x}$Mn$_{x}$As/Ga$_{1 - y}$Al$_{y}$As heterostructures modulation-doped by Be. The FMR experiments provide a direct measure of cubic and uniaxial magnetic anisotropy fields, and their dependence on the doping level. It is found that the increase in doping -- in addition to rising the Curie temperature of the Ga$_{1 - x}$Mn$_{x}$As layers -- also leads to a very significant increase of their uniaxial anisotropy field. The FMR measurements further show that the effective $g$-factor of Ga$_{1 - x}$…
(Ga,Mn)As is at the forefront of research exploring the synergy of magnetism with the physics and technology of semiconductors, and has led to discoveries of new spin-dependent phenomena and functionalities applicable to a wide range of material systems. Its recognition and utility as an ideal model material for spintronics research has been undermined by the large scatter in reported semiconducting doping trends and micromagnetic parameters. In this paper we establish these basic material characteristics by individually optimizing the highly non-equilibrium synthesis for each Mn-doping level …
Various types of magnetism can appear in emerging quantum materials such as van der Waals layered ones. Here, we report the successful doping of manganese atoms into a post-transition metal dichalcogenide semiconductor: SnSe$_2$. We synthesized a single crystal Sn$_{1-x}$Mn$_x$Se$_{2}$ with $\textit{x}$ = 0.04 by the chemical vapor transport (CVT) method and characterized it by x-ray diffraction (XRD) and energy-dispersive x-ray spectroscopy (EDS). The magnetic properties indicated a competition between coexisting ferromagnetic and antiferromagnetic interactions, from the temperature dependenc…
We report the doping dependence of the order of the ferromagnetic metal to paramagnetic insulator phase transition in La1-xCaxMnO3. At x = 0.33, magnetization and specific heat data show a first order transition, with an entropy change (2.3 J/molK) accounted for by both volume expansion and the discontinuity of M ~ 1.7 Bohr magnetons via the Clausius-Clapeyron equation. At x = 0.4, the data show a continuous transition with tricritical point exponents alpha = 0.48+/- 0.06, beta = 0.25+/- 0.03, gamma = 1.03+/- 0.05, and delta = 5.0 +/- 0.8. This tricritical point separates first order (x<0.4) f…
Despite significant potential as energy storage materials for electric vehicles due to their combination of high energy density per unit cost and reduced environmental and ethical concerns, Co-free lithium ion batteries based off layered Mn oxides presently lack the longevity and stability of their Co-containing counterparts. Here, we demonstrate a reduction in this performance gap via chemical doping, with Li$_{1.1}$Ni$_{0.35}$Mn$_{0.55}$O$_2$ achieving an initial discharge capacity of 159 mAhg$^{-1}$ at C/3 rate and a corresponding capacity retention of 94.3% after 150 cycles. We subsequentl…
We have investigated the influence of B - site doping on the crystal and magnetic structure in $La_{0.5}Ca_{0.5}Mn_{1-x}B_{x}O_{3}$ (B= Fe, Ru, Al and Ga) compounds using neutron diffraction, SANS, magnetization and resistivity techniques. The B - site doped samples are isostructural and possess an orthorhombic structure in \textit{Pnma} space group at 300K. A structural transition from orthorhombic to monoclinic is found to precede the magnetic transition to CE - type antiferromagnetic state in few of these samples. On doping with Fe, charge and orbitally ordered CE - type antiferromagnetic s…
Interlayer coupling is of vital importance for manipulating physical properties, e.g. electronic bandgap, in two-dimensional materials. However, tuning magnetic proper-ties in these materials is yet to be addressed. Here, we found a striped antiferromag-netic (sAFM) to ferromagnetic (FM) transition undergoing from monolayer to bilayer and thicker CrS2. This transition is attributed to charge sharing of interlayer S atoms and its resulting charge transfer from Cr d eg to t2g orbitals. The transferred charge reduces a portion of Cr4+ to Cr3+, which enhances the double-exchange mechanism favoring…
Cobalt and silver co-doping has been undertaken in ZnO thin films grown by pulsed laser deposition in order to investigate the ferromagnetic properties in ZnO-based diluted magnetic materials and to understand the eventual relation between ferromagnetism and charge carriers. Hall transport measurements reveal that Ag doping up to 5% leads to a progressive compensation of the native n-type carriers. The magnetization curves show ferromagnetic contributions for all samples at both 5 K and room temperature, decreasing with increasing the Ag concentration. First principles modeling of the possible…
The electronic structure of Li-doped Ni$_{1-x}$Fe$_x$O has been investigated using photoemission spectroscopy (PES) and x-ray absorption spectroscopy (XAS). The Ni $2p$ core-level PES and XAS spectra were not changed by Li doping. In contrast, the Fe$^{3+}$ intensity increased with Li doping relative to the Fe$^{2+}$ intensity. However, the increase of Fe$^{3+}$ is only $\sim 5%$ of the doped Li content, suggesting that most of the doped holes enter the O $2p$ and/or the charge-transferred configuration Ni $3d^8\underline{L}$. The Fe 3d partial density of states and the host valence-band emiss…
To obtain high-performance spintronic devices with high integration density, two-dimensional (2D) half-metallic materials are eagerly pursued all along. Here, we propose a stable 2D material with a honeycomb-kagome lattice, i.e., the Mg3C2 monolayer, based on first-principles calculations. This monolayer is an anti-ferromagnetic (AFM) semiconductor at its ground state. We further demonstrate that a transition from AFM semiconductor to ferromagnetic half-metal in this 2D material can be induced by carrier (electron or hole) doping. This magnetic transition can be understood by the Stoner criter…
Two-dimensional (2D) ferromagnetic materials are considered as promising candidates for the future generations of spintronic devices. Yet, 2D materials with intrinsic ferromagnetism are scarce. High-throughput first-principles simulations are performed in order to screen 2D materials that present a non-magnetic to a ferromagnetic transition upon hole doping. A global evolutionary search is subsequently performed, in order to identify alternative possible atomic structures of the eligible candidates, and 122 materials exhibiting a hole-doping induced ferromagnetism are identified. Their energet…
We report the discovery of a new diluted magnetic semiconductor, Li(Zn,Mn)P, in which charge and spin are introduced independently via lithium off-stoichiometry and the isovalent substitution of Mn2+ for Zn2+, respectively. Isostructural to (Ga,Mn)As, Li(Zn,Mn)P was found to be a p-type ferromagnetic semiconductor with excess Lithium providing charge doping. First principles calculations indicate that excess Li is favored to partially occupy the Zn site, leading to hole doping. Ferromagnetism is mediated in semiconducting samples of relative low mobile carriers with a small coercive force, ind…
Here we report the successful synthesis of a spin- & charge-decoupled diluted magnetic semiconductor (Ca,Na)(Zn,Mn)2As2, crystallizing into the hexagonal CaAl2Si2 structure. The compound shows a ferromagnetic transition with a Curie temperature up to 33 K with 10% Na doping, which gives rise to carrier density of np~10^20 cm^-3. The new DMS is a soft magnetic material with HC<400 Oe. The anomalous Hall effect is observed below the ferromagnetic ordering temperature. With increasing Mn doping, ferromagnetic order is accompanied by an interaction between the local spin and mobile charge, giving …
The electronic structure and magnetic properties of FeGa3 and doped FeGa3 are studied using density functional calculations. An itinerant mechanism for ferromagnetism is found both for n-type doping with Ge and also for p-type doping. Boltzmann transport calculations of the thermopower are also reported.
In order to study the metallic ferromagnetism induced by electron doping in the narrow-gab semiconductor FeSb$_2$, single crystals of FeSb$_2$, Fe$_{1-x}$Co$_x$Sb$_2$ ($0 \le x \le 0.5$) and FeSb$_{2-y}$Te$_y$ ($0 \le y \le 0.4$), were grown by a simplified self-flux method. From powder x-ray diffraction (XRD) patterns, wavelength-dispersive x-ray spectroscopy (WDX) and x-ray Laue diffraction, pure and doped high-quality single crystals, within the selected solubility range, show only the orthorhombic $Pnnm$ structure of FeSb$_2$ with a monotonic change in lattice parameters with increasing th…
The magnetic and electronic properties of strontium titanate with different carbon dopant configurations are explored using first-principles calculations with a generalized gradient approximation (GGA) and the GGA+U approach. Our results show that the structural stability, electronic properties and magnetic properties of C-doped SrTiO3 strongly depend on the distance between carbon dopants. In both GGA and GGA+U calculations, the doping structure is mostly stable with a nonmagnetic feature when the carbon dopants are nearest neighbors, which can be ascribed to the formation of a C-C dimer pair…
Impurity effects on the stability of a ferromagnetic metallic state in a bicritical-state manganite, (La0.7Pr0.3)0.65Ca0.35MnO3, on the verge of metal-insulator transition have been investigated by substituting a variety of transition-metal atoms for Mn ones. Among them, Fe doping exhibits the exceptional ability to dramatically decrease the ferromagnetic transition temperature. Systematic studies on the magnetotransport properties and x-ray diffraction for the Fe-doped crystals have revealed that charge-orbital ordering evolves down to low temperatures, which strongly suppresses the ferromagn…
The effect of Fe doping in the Mn site on the magnetic, transport and structural properties of polycrystalline La1/2Ca1/2MnO3 was studied. Doping with low Fe concentration (< 10%) strongly affects electrical transport and magnetization. Long range charge order is disrupted even for the lowest doping level studied (~2%). For Fe concentration up to 5% a ferromagnetic state develops at low temperature with metallic like conduction and thermal hysteresis. In this range, the Curie temperature decreases monotonously as a function of Fe doping. Insulating behavior and a sudden depression of the ferro…
Versatile features of impurity doping effects on perovskite manganites, $R_{0.6}$Sr$_{0.4}$MnO$_{3}$, have been investigated with varying the doing species as well as the $R$-dependent one-electron bandwidth. In ferromagnetic-metallic manganites ($R$=La, Nd, and Sm), a few percent of Fe substitution dramatically decreases the ferromagnetic transition temperature, leading to a spin glass insulating state with short-range charge-orbital correlation. For each $R$ species, the phase diagram as a function of Fe concentration is closely similar to that for $R_{0.6}$Sr$_{0.4}$MnO$_{3}$ obtained by de…
To understand the magnetic properties of Fe$_3$GeTe$_2$, we performed the detailed first-principles study. Contrary to the conventional wisdom, it is unambiguously shown that Fe$_3$GeTe$_2$ is not ferromagnetic but antiferromagnetic carrying zero net moment in its stoichiometric phase. Fe defect and hole doping are the keys to make this material ferromagnetic, which are shown by the magnetic force response as well as the total energy calculation with the explicit Fe defects and the varied system charges. Further, we found that the electron doping also induces the antiferro- to ferromagnetic tr…
We have employed one of the well-known many-body techniques, density functional theory plus dynamical mean-field theory (DFT + DMFT), to investigate the electronic structure of ferromagnetic monolayer CrI3 as a function of temperature and hole-doping concentration. The computed magnetic susceptibility follows the Curie's law, indicating that the ferromagnetism of monolayer CrI3 originates from localized magnetic moments of Cr atoms rather than Stoner-type itinerant ones. The DFT + DMFT calculations show a different coherent temperature for each spin component, demonstrating apparent strong spi…
Emergence of half-semiconductor behavior and tunable magnetism via carrier doping in Janus VXSe (X=Cl, Br, I) monolayers
Southwest University（西南大学）；Hanhong College, Southwest University（汉弘学院，西南大学）；AECC Hunan Aviation Powerplant Research Institute（中国航发湖南航空发动机研究所）；Chengdu University of Technology（成都理工大学）；Leshan Normal University（乐山师范学院）；Shanghai Jiao Tong University（上海交通大学）
$Na_xCoO_2$ has a fascinating and complex magnetic phase diagram that can be further manipulated by doping. Here, we investigated the effect of electron doping on the magnetic coupling among $Co^{4+}$ ions in $Na_xCoO_2$ using density functional theory based on Hartree-Fock hybrid functional. We found that electron doping through substitutional $Sb_{Co}$ dopants flip the in-plane ferromagnetic coupling among $Co^{4+}$ ions in the undoped compound to antiferromagnetic. Electron doping through interstitial $Cu_{Int}$, however, does not have a similar effect as $Cu_{Int}$ dopant leaves the compou…
We discuss the phase diagram of the two-orbital model of half-doped manganites by calculating self-consistently the Jahn-Teller (JT) distortion patterns, charge, orbital and magnetic order at zero temperature. We analyse the instabilities of these phases caused by electron or hole doping away from half-doping, or by the application of a magnetic-field. For the CE insulating phase of half-doped manganites, in the intermediate JT coupling regime, we show that there is a competition between canting of spins (which promotes mobile carriers) and polaronic self-trapping of carriers by JT defects. Th…
Magnetic doping of topological quantum materials provides an attractive route for studying the effects of time-reversal symmetry breaking. Thus motivated, we explore the introduction of the transition metal Mn into thin films of the Dirac semimetal Cd3As2 during growth by molecular beam epitaxy. Scanning transmission electron microscopy measurements show the formation of a Mn-rich phase at the top surface of Mn-doped Cd3As2 thin films grown using both uniform doping and delta doping. This suggests that Mn acts as a surfactant during epitaxial growth of Cd3As2, resulting in phase separation. Ma…
Understanding the magnetic properties of the various Mn doping configurations that can be encountered in $2H$-MoS$_2$ monolayer could be beneficial for its use in spintronics. Using density functional theory plus Hubbard U (DFT$+$U) approach, we study how a single isolated, double- and triple-substitution configurations of Mn atoms within a MoS$_2$ monolayer could contribute to its total magnetization. We find that the doping-configuration plays a critical role in stabilizing a ferromagnetic state in a Mn-doped MoS$_2$ monolayer. Indeed, the Mn-Mn magnetic interaction is found to be ferromagnt…
Strontium doping transforms manganites of type La(1-x)Sr(x)MnO(3) from an insulating antiferromagnet (x=0) to a metallic ferromagnet (x>0.16) due to the induced charge carriers (holes). Neutron scattering experiments were employed to investigate the effect of Sr doping on a tailor-made compound of composition La(0.7)Sr(0.3)Mn(0.1)Ti(0.3)Ga(0.6)O(3). By the simultaneous doping with Sr2+ and Ti4+ ions the compound remains in the insulating state, so that the magnetic interactions for large Sr doping can be studied in the absence of charge carriers. At TC=215 K there is a first-order reconstructi…
Resistivity and dc magnetization measurements were performed for the polycrystalline Pr$_{0.5}$Ca$_{0.5}$Co$_{1-x}$Fe$_{x}$O$_{3-δ}$ ($x$ = 0, 0.05, 0.10 and 0.15) samples. The as-fabricated samples exhibit ferromagnetic (FM) transition and the transition temperature increases with increasing the iron doping level. Annealing under high oxygen pressure induces a spin-state transition of Co ions in the \emph{iron-free} sample and such transition is reinforced with increasing the annealing oxygen pressure, while the annealing under high oxygen pressure suppresses the ferromagnetic ordering. Contr…
The effect of additional doping of charge impurities was investigated in a ferromagnetic semiconductor Zn$_{1-x}$Cr$_{x}$Te. It was found that the doping of iodine, which is expected to act as an n-type dopant in ZnTe, brought about a drastic enhancement of the ferromagnetism in Zn$_{1-x}$Cr$_{x}$Te while the grown films remained electrically insulating. In particular, at a fixed Cr composition of x = 0.05, the ferromagnetic transition temperature Tc increased up to 300K at maximum due to the iodine doping from Tc = 30K of the undoped counterpart, while the ferromagnetism disappeared due to th…
We applied the generalized Bloch theorem to verify the ground state (most stable state) in monolayer metal diiodides 1T-XI$_{2}$ (X: Fe, Co, and Ni), a family of metal dihalides, using the first-principles calculations. The ground state, which can be ferromagnetic, antiferromagnetic, or spiral state, was specified by a wavevector in the primitive unit cell. While the ground state of FeI$_{2}$ is ferromagnetic, the spiral state becomes the ground state for CoI$_{2}$ and NiI$_{2}$. Since the multiferroic behavior in the metal dihalide can be preserved by the spiral structure, we believe that CoI…
We studied structural, electronic and magnetic properties of a cubic perovskite BaFeO$_{3-δ}$ ($0 \le δ\le 0.5$) within the density functional theory using a generalized gradient approximation and a GGA+U method. According to our calculations, BaFeO$_3$ in its stoichiometric cubic structure should be half-metallic and strongly ferromagnetic, with extremely high Curie temperature ($T_C$) of 700 - 900 K. However, a such estimate of $T_C$ disagrees with all available experiments, which report that $T_C$ of the BaFeO$_3$ and undoped BaFeO$_{3-δ}$ films varies between 111 K and 235 K or, alternativ…
Semiconductor structures using ferromagnetic semiconductors as spin injectors are promising systems for future spintronic devices. Here, we present combined photoluminescence (PL) and time-resolved magneto-optical experiments of a nominally nonmagnetic quantum well(QW) separated by a thin barrier from a ferromagnetic Ga(Mn)As layer. Due to the partial quenching of the PL, we conclude that there is a significant Mn backdiffusion into the QW. Moreover, from the time-resolved measurements, we infer that the Mn leads to n-type doping within the QW, and, in addition, strongly increases the electron…
Diluted ferromagnetic III-V semiconductors typically show a high degree of compensation. Compensation is connected to the presence of comparable densities of charged defects of either sign. This naturally leads to the development of strong correlations between defect positions during growth and annealing. We show that these correlations are required to understand the experimentally observed transport and magnetic properties as well as the persistence of the energy gap upon doping with magnetic ions.
We propose a class of graphene nanoribbons showing strong intrinsic ferromagnetic behavior due to their asymmetry. Such ribbons are based on a zig-zag edged backbone surmounted by a periodic, triangular notched region of variable size. The electronic properties as a function of the topology are investigated. Interestingly, substitutional doping by boron or nitrogen induces half-metallicity. The most effective doping sites can be inferred from the band structure. Given the present rapid development of bottom-up strategies for the synthesis of atomically precise carbon nanostructures the propose…
We successfully dope the magnetically silent double perovskite semiconductor Sr2GaSbO6 to induce ferromagnetism and tune its band gap, with Ga3+ partially substituted by the magnetic trivalent cation Mn3+, in a rigid cation ordering with Sb5+. Our new ferromagnetic semiconducting Sr2Ga1-xMnxSbO6 double perovskite, which crystallizes in tetragonal symmetry (space group I4/m) and has tunable ferromagnetic ordering temperature and band gap, suggests that magnetic ion doping of double perovskites is a productive avenue towards obtaining materials for application in next-generation oxide-based spin…
Magic-angle twisted bilayer graphene (MATBG) is notable as a highly tunable platform for investigating strongly correlated phenomena such as high-$T_c$ superconductivity and quantum spin liquids, due to easy control of doping level through gating and sensitive dependence of the magic angle on hydrostatic pressure. Experimental observations of correlated insulating states, unconventional superconductivity and ferromagnetism in MATBG indicate that this system exhibits rich exotic phases. In this work, using density functional theory calculations in conjunction with the effective screening medium…
Fe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature > 450 K with a low-temperature transition from ferromagnetic to spin-glass state due to canting of the disordered surface spins in the nanoparticle system. Local magnetic probes like EPR and Mossbauer indicate the presence of Fe in both valence states Fe2+ and Fe3+. We argue that the presence of Fe3+ is due to the possible hole doping in t…
We theoretically study the carrier doping effect for magnetism in a stacked-kagome system $\rm{{Co}_3{Sn}_2{S}_2}$ based on an effective model and the Hartree-Fock method. We show the electron filling and temperature dependences of the magnetic order parameter. The perpendicular ferromagnetic ordering is suppressed by hole doping, wheres undoped $\rm{{Co}_3{Sn}_2{S}_2}$ shows magnetic Weyl semimetal state. Additionally, in the electron-doped regime, we find a non-collinear antiferromagnetic ordering. Especially, in the non-collinear antiferromagnetic state, by considering a certain spin-orbit …
Intrinsic ferromagnetism is a crucial ingredient to realize quantum anomalous Hall effect in quasi two dimensional materials, thus the search of intrinsic ferromagnetic topological materials is one of the most concerned issues in the field of topological phases of matter. In this work, combining magnetotransport measurements, first principles calculations, and angle-resolved photoemission spectroscopy studies, we find that in MnSb6Te10, the n = 2 member of the MnSb2Te4/(Sb2Te3)n family, the strong magnetic competition realizes a fragile ferromagnetic ground state, which whereas easily enters i…
