AFM Ground State Research Articles

First principles investigation of 3d transition metal doped SnO monolayer based diluted magnetic semiconductors

The two-dimensional (2D) SnO monolayer attracted capacious recognition on account of its incomparable applications in nanoelectronics. Diluted magnetic semiconductors (DMS) are realized via doping of transition metals (TM) in semiconductors for usage in spintronic devices. This work is carried out using first-principles method to substitute 3d TM impurity atoms (Sc, Ti, V, Cr, Co, Ni, Cu and Zn) in place of Sn cation sites in the SnO monolayers. The analysis of modification resulted after the doping process is carried out to investigate the changes in the structural, electronic and magnetic properties of the materials. The calculated formation energy is utilized to examine the structural stability of the doped materials. The material doped with Sc, Ti, V, Cr, Co and Cu showed magnetic behavior while no magnetization is detected in case of doping with Ni and Zn. The results are discussed in the light of calculated crystal field splitting and exchange interactions between the two impurity-doped atoms. The magnetic ground state and Curie temperature of the DMS are also estimated. The Sc, V and Co doping has a ferromagnetic ground state while Ti, Cr and Cu doped structures got the AFM ground state. The mixing of TM-3d orbitals with the host s and p states is considered responsible for magnetism and the magnetic moment. The outcomes of the study point out that the TM doped SnO monolayer based DMS may be helpful to realize the spin-TFT devices in the near future.

Role of cationic size mismatch and effect of disorder in mixed valent manganites

Comparative studies of structure, magnetism, and magnetoresistance (MR) have been carried out in A-site ordered NdBaMn2O6 (O-NB), A-site disordered NdBaMn2O6 (D-NB) and A-site disordered NdCaMn2O6 (D-NC). O-NB, where A-site cations, Nd3+ and Ba2+ (of different ionic sizes) are arranged periodically, undergoes structural transition with temperature, while no structural change is present in D-NB where A-site cations are arranged randomly. However, structural transitions are observed in D-NC where Nd3+ and Ca2+ have similar ionic sizes. Magnetization (M) data shows O-NB has AFM ground state associated with a lower structurally symmetric phase and an FM ground state is observed for D-NB with higher structural symmetry. However, AFM ground state is observed in D-NC similar to that of O-NB. Both the disorder systems exhibit semiconductive transport characteristics over the entire temperature range. The resistivity data of disorder compounds have been fitted with different theoretical models to elucidate the conduction process in these systems. Further, MR studies depict a three times higher value of MR in both disorder compounds compared to that of order one. However, the behavior of MR with H is different for D-NB and D-NC, implying a different origin of this large MR in these compounds. We believe that the different magnetic ground state of D-NB and D-NC is the possible origin of their distinct MR behavior to the magnetic field.

Magnetotransport and magnetic properties of Cr-modified Mn2Sb epitaxial thin films.

High-quality Mn2-xCrxSb (x = 0.01, 0.04, and 0.1) epitaxial thin films were grown on SrTiO3 (STO) (001) single-crystal substrates using molecular beam epitaxy. Magnetotransport and magnetic measurements reveal that the x = 0.01 sample undergoes a quasi-ferrimagnetic (I) [Q-FIM(I)]-to-ferrimagnetic (II) [FIM(II)] spin reorientation (SR) transition and a giant magnetoresistance (MR) associated first-order ferrimagnetic(II)-to-antiferromagnetic (AFM) phase transition upon cooling, resulting in the AFM ground state with a weak in-plane net moment. Upon increasing the doping level from x = 0.01 to 0.1, both the SR transition and the first-order magnetic transition are suppressed. For x = 0.1, the former transition is suppressed, leaving only the Q-FIM(I)-to-AFM transition within the whole temperature region. TAFM-FIM shows almost similar changes upon the application of either in-plane or out-of-plane magnetic fields. TAFM-FIM values of the x = 0.01 and 0.04 samples are much higher than those of the Mn2-xCrxSb bulk with similar doping levels, which can be understood by the clamping effect from STO substrates. For each thin-film sample, the MR effect is observed near TAFM-FIM and disappears in the high temperature Q-FIM(I) phase and low temperature AFM phase, indicating that MR is related to the spin-dependent electron scattering during the first-order magnetic phase transition. Based on the magnetotransport and magnetic data, a magnetic phase diagram is established for the Mn2-xCrxSb films in the low doping level region.

Magnetism of two-dimensional honeycomb layered Na2Ni2TeO6 driven by intermediate Na-layer crystal structure

The microscopic spin-spin correlations in the 2D layered spin-1 honeycomb lattice compound Na2Ni2TeO6 have been investigated by neutron diffraction and inelastic neutron scattering. The honeycomb lattice of spin-1 Ni2+ ions, within the crystallographic ab planes, are well separated along the c axis by an intermediate Na layer whose crystal structure contains chiral nuclear density distributions of Na ions. The chirality of the alternating Na layers is opposite. Such alternating chirality of the Na layer dictates the magnetic periodicity along the c axis where an up-up-down-down spin arrangement of the in-plane zigzag AFM structure is found. Besides, the above described commensurate (CM) zigzag AFM order state is found to coexist with an incommensurate (ICM) AFM state below the TN ~ 27.5 K. The ICM state is found to appear at much higher temperature ~ 50 K and persists down to lowest measured temperature of 1.7 K. Our reverse Monte Carlo (RMC) analysis divulges a two dimensional (2D) magnetic correlations (within the ab plane) of the ICM AFM state over the entire temperature range 1.7-50 K. Further, the spin-Hamiltonian has been determined by carrying out inelastic neutron scattering experiments and subsequent linear spin-wave theory analysis which reveals the presence of competing inplane exchange interactions up to 3 rd nearest neighbours consistent with the zigzag AFM ground state, and weak interplanar interaction as well as a weak single-ion-anisotropy. The values of the exchange constants yield that Na2Ni2TeO6 is situated well inside the zigzag AFM phase (spans over a wide ranges of J2/J1 and J3/J1 values) in the theoretical phase diagram. The present study, thus, provides a detailed microscopic understanding of the magnetic correlations and divulges the intertwining magneto-structural correlations.

Theoretical investigation of the effect of native defects on spin polarization and antiferromagnetic state in Co3O4

The effect of the native defects on the spin polarization and the antiferromagnetic state of Co3O4 was investigated using the first-principles calculations. The results reveal that the AFM ground state of Co3O4 is changed to a ferromagnetic state by introducing one OCo antisite defect at the A/B site, while O vacancy can induce the highest spin polarization and most stable AFM state. The interactions between two O vacancies with different distances are all AFM interactions and the strength of AFM interaction is strongest at the distance of 2.85 Å. The theoretical investigation suggests an effective route to improve the spin polarization and stability of AFM state by defect engineering, promoting the applications of Co3O4 in antiferromagnetic spintronics.

Spin and Orbital Effects on Asymmetric Exchange Interaction in Polar Magnets: M(IO3)2 (M = Cu and Mn).

Magnetic polar materials feature an astonishing range of physical properties, such as magnetoelectric coupling, chiral spin textures, and related new spin topology physics. This is primarily attributable to their lack of space inversion symmetry in conjunction with unpaired electrons, potentially facilitating an asymmetric Dzyaloshinskii-Moriya (DM) exchange interaction supported by spin-orbital and electron-lattice coupling. However, engineering the appropriate ensemble of coupled degrees of freedom necessary for enhanced DM exchange has remained elusive for polar magnets. Here, we study how spin and orbital components influence the capability of promoting the magnetic interaction by studying two magnetic polar materials, α-Cu(IO3)2 (2D) and Mn(IO3)2 (6S), and connecting their electronic and magnetic properties with their structures. The chemically controlled low-temperature synthesis of these complexes resulted in pure polycrystalline samples, providing a viable pathway to prepare bulk forms of transition-metal iodates. Rietveld refinements of the powder synchrotron X-ray diffraction data reveal that these materials exhibit different crystal structures but crystallize in the same polar and chiral P21 space group, giving rise to an electric polarization along the b-axis direction. The presence and absence of an evident phase transition to a possible topologically distinct state observed in α-Cu(IO3)2 and Mn(IO3)2, respectively, imply the important role of spin-orbit coupling. Neutron diffraction experiments reveal helpful insights into the magnetic ground state of these materials. While the long-wavelength incommensurability of α-Cu(IO3)2 is in harmony with sizable asymmetric DM interaction and low dimensionality of the electronic structure, the commensurate stripe AFM ground state of Mn(IO3)2 is attributed to negligible DM exchange and isotropic orbital overlapping. The work demonstrates connections between combined spin and orbital effects, magnetic coupling dimensionality, and DM exchange, providing a worthwhile approach for tuning asymmetric interaction, which promotes evolution of topologically distinct spin phases.

Proximity-Induced Novel Ferromagnetism Accompanied with Resolute Metallicity in NdNiO3 Heterostructure.

Employing X‐ray magnetic circular dichroism (XMCD), angle‐resolved photoemission spectroscopy (ARPES), and momentum‐resolved density fluctuation (MRDF) theory, the magnetic and electronic properties of ultrathin NdNiO3 (NNO) film in proximity to ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) layer are investigated. The experimental data shows the direct magnetic coupling between the nickelate film and the manganite layer which causes an unusual ferromagnetic (FM) phase in NNO. Moreover, it is shown the metal–insulator transition in the NNO layer, identified by an abrupt suppression of ARPES spectral weight near the Fermi level (E F), is absent. This observation suggests that the insulating AFM ground state is quenched in proximity to the FM layer. Combining the experimental data (XMCD and AREPS) with the momentum‐resolved density fluctuation calculation (MRDF) reveals a direct link between the MIT and the magnetic orders in NNO systems. This work demonstrates that the proximity layer order can be broadly used to modify physical properties and enrich the phase diagram of RENiO3 (RE = rare‐earth element).

Ab-Initio Study of Magnetically Intercalated Platinum Diselenide: The Impact of Platinum Vacancies.

We study the magnetic properties of platinum diselenide (PtSe2) intercalated with Ti, V, Cr, and Mn, using first-principle density functional theory (DFT) calculations and Monte Carlo (MC) simulations. First, we present the equilibrium position of intercalants in obtained from the DFT calculations. Next, we present the magnetic groundstates for each of the intercalants in along with their critical temperature. We show that Ti intercalants result in an in-plane AFM and out-of-plane FM groundstate, whereas Mn intercalant results in in-plane FM and out-of-plane AFM. V intercalants result in an FM groundstate both in the in-plane and the out-of-plane direction, whereas Cr results in an AFM groundstate both in the in-plane and the out-of-plane direction. We find a critical temperature of <0.01 K, 111 K, 133 K, and 68 K for Ti, V, Cr, and Mn intercalants at a 7.5% intercalation, respectively. In the presence of Pt vacancies, we obtain critical temperatures of 63 K, 32 K, 221 K, and 45 K for Ti, V, Cr, and Mn-intercalated , respectively. We show that Pt vacancies can change the magnetic groundstate as well as the critical temperature of intercalated , suggesting that the magnetic groundstate in intercalated can be controlled via defect engineering.

Unraveling the effects Mn-site doping on structural, magnetic and magnetotransport properties of Nd0.67Sr0.33Mn0.9T0.1O3 (T= Mn, Fe, Cr, Ni)

The present work reports the effects Mn site doping on the structural, magnetic and magnetotransport properties of Nd0.67Sr0.33Mn0.9T0.1O3, where T = Mn, Fe, Cr and Ni. Structural analysis based on Rietveld refinement confirms that the samples crystallize in orthorhombic structure with Pbnm space group. A detailed investigation on the FTIR spectra hints to the improved metallic character of Nd0.67Sr0.33Mn0.9Mn0.1O3 and Nd0.67Sr0.33Mn0.9Ni0.1O3 samples. Strong ferromagnetic character of Nd0.67Sr0.33Mn0.9Mn0.1O3 and Nd0.67Sr0.33Mn0.9Cr0.1O3 is revealed from ZFC-FC magnetization studies, while the Fe and Ni doped samples possess strong AFM ground state. An irreversible metamagnetic transition is discernible from the hysteresis curve of Nd0.67Sr0.33Mn0.9Fe0.1O3. Transport studies reveal a charge ordered state in Fe doped sample close to its spin glass transition temperature, Tg = 65 K. Nd0.67Sr0.33Mn0.9Mn0.1O3 behave like a typical double exchange material with nearly same TC and TP values, whereas for all other samples TP lie much below TC. Low resistive state materialized in a strong AFM material as observed in Nd0.67Sr0.33Mn0.9Ni0.1O3, is rarely observed in manganites. Colossal MR values exhibited by Fe and Ni doped samples are understood based on phase separation scenario of manganites. Large dissimilarities evident in the magnetic and electronic properties of the compounds, though the dopant ions possess nearly same ionic size, are attributed to differences in their electronic configuration. Resistivity behavior of samples in different temperature regimes are comprehended based on existing models of conduction.

Stability of atomic-sized skyrmions in antiferromagnetic bilayers

We perform a stability analysis of an isolated atomic-sized antiferromagnetic skyrmion (AFM-Sk), formed on the superior layer of a magnetic bilayer. The coupling between both square lattices acts as an effective staggered magnetic field that stabilizes the AFM-Sk and reduces its radius. A suitable anisotropy constant of the bottom layer material keeps it close to the homogeneous AFM state. We compare the energy of the AFM-Sk with the energy of the AFM ground state. In addition, an estimation of the energy barrier that protects the skyrmion from being destabilized is provided and its value determined to be in the order of ∼300 K. The remarkable reduction in the skyrmion radius towards atomic size and avoiding an external magnetic field are key points in order to increase our ability to manipulate AFM-Sk on skyrmionic devices. Our calculations provide an insight into novel ways to create and manipulate AFM-Sk at the atomic scale.

First-principles study on electronic and magnetic properties of (Al,Mn) codoped BaZn2As2

Based on the first-principles calculations, the electronic structure and magnetic properties of (Al,Mn) codoped BaZn2As2 have been investigated. We find that only Al atom doped BaZn2As2 is a nonmagnetic semiconductor with a band gap of 0.7 eV. Exploiting (Zn2+,Mn2+) substitutions to introduce magnetic moments, the Ba(Zn,Mn)2As2 system prefers the AFM ground state. For one Al atom and Mn codoped BaZn2As2, the long-range Mn-Mn pair configuration turns into FM state, while the nearest neighbour Mn-Mn pair configuration remains AFM state. However, because of more electron introduced by increasing the Al dopant, the nearest neighbour Mn-Mn pair configuration transfers from AFM to FM. Our investigation reveals that the FM coupling is mediated by the exchange interaction of Mn-3d orbitals and As-4p orbitals. The FM originates from a strong p-d exchange interaction occurred between carriers and localized spin for the (Ba,Al)(Zn,Mn)2As2.

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe1−xCox)2As2

Results of inelastic neutron scattering measurements are reported for two annealed compositions of ${\mathrm{Ca}(\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}{\mathrm{As}}_{2},x=0.026$ and 0.030, which possess stripe-type antiferromagnetically ordered and superconducting ground states, respectively. In the AFM ground state, well-defined and gapped spin waves are observed for $x=0.026$, similar to the parent ${\mathrm{CaFe}}_{2}{\mathrm{As}}_{2}$ compound. We conclude that the well-defined spin waves are likely to be present for all $x$ corresponding to the AFM state. This behavior is in contrast to the smooth evolution to overdamped spin dynamics observed in ${\mathrm{Ba}(\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}{\mathrm{As}}_{2}$, wherein the crossover corresponds to microscopically coexisting AFM order and SC at low temperature. The smooth evolution is likely absent in ${\mathrm{Ca}(\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{)}_{2}{\mathrm{As}}_{2}$ due to the mutual exclusion of AFM ordered and SC states. Overdamped spin dynamics characterize paramagnetism of the $x=0.030$ sample and high-temperature $x=0.026$ sample. A sizable loss of magnetic intensity is observed over a wide energy range upon cooling the $x=0.030$ sample, at temperatures just above and within the superconducting phase. This phenomenon is unique amongst the iron-based superconductors and is consistent with a temperature-dependent reduction in the fluctuating moment. One possible scenario ascribes this loss of moment to a sensitivity to the $c$-axis lattice parameter in proximity to the nonmagnetic collapsed tetragonal phase and another scenario ascribes the loss to a formation of a pseudogap.

Electronic Structures of Silicene Nanoribbons: Two-Edge-Chemistry Modification and First-Principles Study.

In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same sp2 hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings.

CO-doping effects on the transport and magnetic properties of FeTe

Here we report a systematic investigation of Co-doping effects on the magnetism and transport properties of Fe1+yTe single crystals. It is found that the anti-ferromagnetism transition temperature decreases upon Co doping, and a spin-glass like behavior emerges at low temperature. With substituting more than x=0.09 Co for Fe, both the metallic behavior and the structural transition disappear, but the density of states at Fermi-level does not change significantly. These results suggest that Co doping does not act as carrier doping but is more likely to bring in random magnetic scatters. In addition, the analysis of RH measurements reveals that the Fermi-level reconstruction is not closely related to the long rang AFM transition, which further supports for the local moment picture with frustrated character in dominating the AFM ground state of Fe1+yTe.

Ferromagnetism in alkali-metal-doped AlP: An ab initio study

By using first-principle calculations within the generalized gradient approximation, we investigated the magnetic and electronic properties of Group IA alkali-metal (Li, Na, K)-doped AlP. The main purpose of this study is to determine the effect that different types of alkali dopants have on the magnetic behavior of AlP. The magnetic moment induced by the Li dopant is negligible in (2×2×2) Li-doped AlP supercell. However, it is also found that the magnetism is affected by the Li doping concentration. The Na and K dopants in AlP induce a net magnetic moment of 2.0μB. Half-metallic characteristics are achieved in K-doped AlP. The calculated density of states and the spin density distribution of Na- and K-doped AlPs show that the magnetism derives from the p–p interaction between the dopants and the neighboring anions. However, the spontaneous polarization cannot occur in Na-doped AlP. The K-doped AlP has the AFM ground state which is the unstable at room temperature. The results reveal that the Na- and K-doped AlPs are unlikely to be potential DMSs for the development of new spintronic devices.

Magnetic properties in CdS monolayer doped with first-row elements: A density functional theory investigation

Using first-principles calculations, we have studied the structural, electronic, and magnetic properties in CdS monolayer doped with nonmagnetic (NM) atoms X (X = B, C, N, and O). The total magnetic moments are about 1.0, 2.0, 1.0, and 0.0 µB per supercell for the B-, C-, N-, and O-doped systems, respectively. As the electronegativity of X element increases, the local magnetic moment tends to localize and the impurity states gradually approach the valence band maximum of the host CdS. We find that the CdS monolayer with one S atom per supercell substituted by a B or C atom is half-metallic (HM), while that with an N atom per supercell is a ferromagnetic (FM) semiconductor. As for the one-oxygen doped case, the system still remains a semiconductor. Upon two S atoms per supercell substituted by X (=B, C, and N) atom, the X-doped CdS systems exhibit various magnetic ground states. As a consequence of the competition between double-exchange and super-exchange, the two-B-doped CdS system displays NM and anti-magnetic (AFM) behaviors, while the two-C-doped CdS system shows HM ferromagnetism with a Curie temperature of 280 K. However, the two-N-doped CdS system is a semiconductor with weakly AFM ground state. Our study demonstrates that the NM elements doping is an efficient route to tune the magnetic and electronic properties in CdS monolayers.

Structural and electromagnetic properties of double C chains decorated zigzag silicene nanoribbon

Using the first-principles calculation, we investigate the structural and electromagnetic properties of the zigzag edge Si nanoribbons (ZSiNRs) decorated with double C chains. The results show that double C chains decorated ZSiNRs are always metallic independent of the ribbon width. The defect states contributed from double C chains are composed of two degenerated bands across the Fermi level. The perfect ZSiNR has a FM ground state, while double C chains decorated one have an AFM ground state. The C chains are always close to straight ones thereby resulting in a transverse contraction near the C chains and thus the ribbon width. The C–Si bond displays an ionic binding feature and the C–H bond is a typical covalent one because of the electronegativity and the bound force difference between H, C and Si atoms.

First-principles LDA+U study of magnetism in CuxIn1−xN

We have carried out First-principles spin-polarized calculations in order to study the electronic structure and magnetism in Cu-doped InN using the LDA+U and LDA formalisms within density functional theory (DFT) with a plane-wave ultrasoft pseudopotential scheme. We found a stable ferromagnetic state in Cu0.0625In0.9375N with a total magnetization of 1.98μB per supercell, indicating Cu orders ferromagnetically in InN. The results indicate that the ferromagnetic ground state originates from the hybridized Cu(3d)–N(2p)–In(5p)–N(2p) chain formed through p–d coupling. Formation energy and ground state calculations have been performed for ferromagnetic and antiferromagnetic states of CuxIn1−xN (x=0,0625 and 0,125) by LDA+U and LDA formalisms. A weak ferromagnetic behavior for CuxIn1−xN (x=0,125) was found. The results predicted an AFM ground state for cases where the Cu atoms are closer. For longer Cu–Cu distances a stable FM ground state was found. This ferromagnetic behavior in CuxIn1−xN (x=0,125) could be tuned with In or N vacancies.

Field-induced phases in UPt2Si2

The tetragonal compound UPt2Si2 has been characterised as a moderately mass enhanced system with an antiferromagnetic ground state below T_N = 32 K. Here, we present an extensive study of the behavior in high magnetic fields. We have performed pulsed field magnetization and static field resistivity measurements on single crystalline samples UPt2Si2. Along the crystallographic a axis, at low temperatures, we find a metamagnetic-like transition in fields of the order 40 T, possibly indicating a first order transition. Along the crystallographic c axis, in magnetic fields of B>= ~24 T, we find distinct anomalies in both properties. From our analysis of the data we can distinguish new high field phases above the AFM ground state. We discuss the emergence of these new phases in the context of Fermi surface effects and the possible occurrence of a Lifshitz or electronic topological transition, this in contrast to previous modellings of UPt2Si2 based on crystal electric field effects.

The magnetism for NN AFM ground state in Fe-based superconductor: Sr 1− xK xFe 2As 2

The crystal structure, magnetism properties, and density of states for FeAs layered compound SrFe 2As 2 have been investigated by using the density functional theory (DFT) method. The magnetism under a checkerboard nearest neighbor anti-ferromagnetic (NN AFM) and ferromagnetic (FM) order ground-state have been analyzed with substitution for Sr with K ion in Sr 1− x K x Fe 2As 2. The results indicate that the distortion of FeAs tetrahedrons is sensitive to the electron doping concentration. The system magnetism was suppressed by K doping in NN-AFM ground state instead of FM. The density of states at Fermi level N ( E F ) under NN AFM ground state would be regarded as a driving force for the increased T c of Sr 1− x K x Fe 2As 2 system as observed experimentally. Our calculation reflects that NN AFM type spin fluctuation may still exist in the Sr 1− x K x Fe 2As 2 system and it may be an origin of strong spin fluctuation in this system besides the spin density wave (SDW) states.