Investigation on structural electronic and magnetic properties of perovskites srmo3 m mn and co via gga and gga+u methods

Journal of Science: Advanced Materials and Devices (2017) 115e122 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article Investigation on structural, electronic and magnetic properties of perovskites SrMO3 (M ¼ Mn and Co) via GGA and GGA ỵ U methods M Musa Saad H.-E.* Department of Physics, College of Science, Qassim University, Buraidah 51452, Saudi Arabia a r t i c l e i n f o a b s t r a c t Article history: Received November 2016 Received in revised form February 2017 Accepted February 2017 Available online 22 February 2017 In this study, two transition-metal perovskites SrMO3 (M ¼ Mn and Co) of interest were studied Their structural, electronic and magnetic properties were investigated via the full-potential linear muffin-tin orbital (FP-LMTO) method within a generalized gradient approximation (GGA) and GGA ỵ U in the framework of the density functional theory (DFT) At room temperature, both compounds of SrMnO3 and SrCoO3 crystallize in a cubic structure, with space group of Pm3m (no 221) in a single phase, having the lattice constants of a ¼ 3.806 Å and a ¼ 3.740 Å, respectively The calculated results are in good agreement with the experimental results DFT calculations reveal strong hybridization between Mn (3d) and Co (3d) and the O (2p) orbitals, and the conduction bands were found to be raised from the hybridized M (3d)eO (2p) orbitals The spin magnetic moments were systemically calculated based on double-exchange interaction M4ỵeOeM3ỵ in SrMO3 â 2017 The Author Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Magnetic materials Perovskites Physical properties DFT GGA method Introduction Perovskites AMO3 have been termed as inorganic changeable oxides due the large flexibility of their crystal structure Many different inorganic oxides take this or related crystal structure since the parent structure easily distorts or adopts to the relative sizes of A and M ions forming the perovskite AMO3 Consequently, the flexibility of the crystal structure of perovskite AMO3 and its ability to accommodate wide range of cations with different ionic sizes and oxidation states in A and M sites are at the origin of the large variety of perovskite compounds with a wide range of physical properties The ideal perovskite AMO3 crystallizes in cubic structure; it consists of MO6 octahedra connected to each other by corner sharing oxygen, and A-cations occupy the 12-fold coordination sites surrounding by eight MO6 octahedra Therefore, the ionic radius of the A ion is larger than that of the M ion and the presence of the different-size cation sites enables a wide variety of perovskite-type oxides For example, the crystal structure of alkaliearth manganese perovskites AMnO3 (A2ỵ ẳ Ca, Sr, Ba) reects the importance of A2ỵ size, where the ionic radius increases from 1.98 for Ca2ỵ to 2.15 for Sr2ỵ and 2.24 for Ba2ỵ In AMnO3 * Fax: ỵ966 163800911 E-mail address: musa.1964@gmail.com Peer review under responsibility of Vietnam National University, Hanoi series, CaMnO3 crystallizes in an orthorhombic derivative of the ideal cubic SrMnO3 [1], containing intermediately sized ions, crystallizes in both cubic and hexagonal and this is a rare example of perovskites having alternating crystal structures While BaMnO3 exhibits hexagonal [2] in which all MnO6 octahedra share faces along the c axis in the crystal Hexagonal structure in SrMnO3 is a 4H-type with alternating face sharing and corner sharing along the c axis The hexagonal modification is stabled up to about 1035  C where it transferred into an ideal cubic in high temperature [2,3] During the last decades, transition-metal perovskites have been a hot topic of the experimental and theoretical research due to their exclusive physical properties, such as ferroelectric in BaTiO3 [4], multiferroic in BiFeO3 [5], high Curie-temperature (TC) in SrRu1ÀxCrxO3 [6] and p-type conducting [7] The interest in transition-metal perovskites was derived from their potential applications For example, colossal magnetoresistance (CMR) in Pr0.7Ca0.3MnO3 [8], spin-filter-type magnetic tunnel junction (MTJ) barriers in La0.1Bi0.9MnO3 [9], magnetic sensors and memory devices in reading heads in SrTiO3 [10,11], electrolytes in solid oxide fuel cells (SOFC) in Y-doped BaCeO3 [12], proton conducting fuel cell (PCFC) in La0.7Sr0.3FeO3Àa [13], etc Moreover, transition-metal perovskites were reported as materials with half-metallic (HM) and MR nature, such as in PrMnO3 [14], Pr1ÀxSrxMnO3 [15], La0.7Ca0.3MnO3 [16] and La1xSrxCoO3 [17] In doped manganite with mixed Mn3ỵ (3d4; t32g e1g ) and Mn4ỵ (3d3; t32g e0g ) valence-states, the hopping of eg electrons occurs http://dx.doi.org/10.1016/j.jsamd.2017.02.001 2468-2179/© 2017 The Author Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 116 M Musa Saad H.-E / Journal of Science: Advanced Materials and Devices (2017) 115e122 between two partially filled 3d orbitals of neighboring Mn3ỵeMn4ỵ This can be simplied by the pdds orbital overlap Mn3ỵ (e1g)eO (2ps)eMn4ỵ (e0g) and the strong onsite Hund coupling between t2g core spins and the eg electrons Such mechanism is known as double-exchange (DE) interaction; it brings about the simultaneous onset of ferromagnetic (FM) and metallic nature Also, another mechanism in doped manganites is the antiferromagnetic (AFM) super-exchange (SE) interaction via the pddp orbital overlap Mn3ỵ t42g ịeO (2pp)eMn4ỵ ðt32g Þ Therefore, the presence of FM-DE and AFM-SE interactions along with the presence of disorder plays an important role in determining the electronic and magnetic properties of doped manganites Transition-metal perovskites have been the subject of many research studies due to their unique properties, such as semiconducting behavior, spin-polarization, metallic or half-metallic (HM), ferromagnetic (FM), antiferromagnetic (AF), ferroelectric (FE), etc Among this family, the pure and doped SrMO3 containing Mn and Co have attracted much attention in many fundamental and applied fields of solid-state physics, solid-state chemistry and material science because of the unusual combination of their structural, electronic and magnetic properties [2,3] SrMO3 (M ¼ Mn, Co) compounds cover a variety of technological applications, such as use in semiconductor products, solid oxide fuel cells, design magnetic memories, read head in hard disks, tunnel magnetic junctions, multiferroics applications, gas diffusion membranes, etc [10e15] In this study, motivated by observation of these remarkable properties in perovskites SrMnO3 and SrCoO3, the structural, electronic and magnetic properties of perovskites SrMO3 (M ¼ Mn and Co) are investigated using the full potential linear muffin-tin orbital method according to density functional theory (DFT) Moreover, an attempt is made to explore the effect of exchange-correlation energy U and M4ỵ-site with 3d transitionmetal ions, M4ỵ ẳ Mn4ỵ and Co4ỵ, on the structural, electronic and magnetic properties The electronic and magnetic results will provide some information on the DE and SE interactions of M4ỵeOeM3ỵ in both of the 90 and 180 arrangements in SrMO3 DFT calculations The calculation of the properties for SrMO3 (M ¼ Mn and Co) was based on the first-principles density functional theory (DFT) [18], via the full-potential linear muffin-tin orbital (FP-LMTO) method [19] Electronic and magnetic properties were obtained from the generalized gradient approximation (GGA) [20], and the exchange-correlation parameterization of PerdeweWang (PW91) [20] was employed in GGA Unluckily, GGA cannot successfully describe the 3d states, so, this lack was corrected by adding exchange-correlation terms to GGA using the GGA ỵ U method [21] GGA ỵ U yields quite satisfying results for correlated perovskites by exploiting correlation parameters, Coulomb repulsion (U) and Hund exchange (J) [22,23] For M (3d) ions, the reasonable values U ¼ 4.0 eV and J ¼ 0.96 eV were employed [22e24], and their settings were examined by the total energy convergence reached in the calculations The cutoff-energy was set to 450 eV and   k-points grids were set in the irreducible part of Brillouin zone To find the stable state, the energy convergence criterion for the electronic selfconsistent calculation was set to 0.001 meV The WignereSeitz radii of the muffin-tin (MT) spheres were set to 2.50, 2.0 and 1.5 a.u for Sr, M and O atoms, respectively In addition, the effect of spineorbit coupling (SOC) was included in the calculations by using the scalar relativistic method (GGA ỵ SOC) and (GGA ỵ SOC ỵ U) based on Dirac equation [19] The full relativistic effects were calculated by using the Dirac equation for core states, whereas the scalar relativistic approximation was used for the valance states [25] Including SOC effect is important for investigating the electronic and magnetic properties of SrMO3 due to the presence of the relatively heavy atoms The SOC was included in a self-consistent manner by solving the radial Dirac equation for the core electrons and evaluated based on the second variation treatment [25,26]; thus, the total angular momentum coupled the orbital angular momentum to the spin of the valence and semi-core states of M (3d) Results and discussion 3.1 Structural properties In crystalline material, the large ion O2À (R ¼ 1.44 Å) is combined with a transition-metal having small ionic radius, such Mn2ỵ (R ẳ 0.67 ), Co2ỵ (R ẳ 0.65 ) and Ni2ỵ (ẳ 0.69 ), the resulting structure can be looked upon as close packed oxygen ions with transition-metal ions in the interstitials This is observed for many inorganic compounds with oxygen ions and transition-metal of valence ỵ2, e.g Mn2ỵO2, Co2ỵO2 and Ni2ỵO2 In these crystal structures, the O2À ions form a cubic close packed (ccp) lattice with the transition-metal ions in the octahedral interstitials, i.e the rocksalt (NaỵCl) structure Replacing one-fourth of the oxygen with a cation of approximately the same radius as O2À, e.g alkali-earth element (A ẳ Ca2ỵ, Sr2ỵ or Ba2ỵ) reduces the number of octahedral voids, occupied by a small M-cation, to one-fourth The resulted formula can be written as AMX3 and this crystal represented the perovskite structure, where the anion X is often O2À but also other large ions such as FÀ and ClÀ are possible This mineral is stable perovskite type, which is one of the fundamental crystal structures Perovskite SrMO3 is a centrosymmetric solid with a typical cubic perovskite structure in Pm3m space group, in which the Sr2ỵ cations are 12-fold coordinated forming cuboctahedral SrO12 clusters, whereas the M4ỵ cations are 6-fold coordinated [27] The octahedral MO6 clusters form the framework of the cubic structure, where the Sr2ỵ, M4ỵ and O2 atoms occupy the cube corners and the edge centers, respectively, as shown in Fig From GGA calculations, the obtained equilibrium lattice constants are a ¼ 3.806 Å for M ¼ Mn, and a ¼ 3.740 Å for M ¼ Co in a good agreement with the previous theoretical values [28,29], as well as with the experiments [30,31] Moreover, similar calculations are repeated by the GGA ỵ U method; however, the crystal structure is only slightly changed with respect the GGA one Table shows the structural properties of the unit cell for perovskites SrMO3 (M ẳ Mn4ỵ and Co4ỵ) Crystal symmetry, space group, lattice constant, unit cell volume, ionic radius, tolerance factor, atomic sites and positions, bond distance and bond angle 3.2 Electronic properties In this part, the effects of M-site substitution, spineorbit coupling (SOC) and exchange-correlation energy U on electronic properties of SrMO3 (M ¼ Mn and Co) are described Therefore, the total and partial density of states (DOS) are calculated within the DFT by using four methods GGA, GGA ỵ SOC, GGA ỵ U and GGA ỵ SOC ỵ U, and plotted in Figs 2e4, in the range 8.0 eV to ỵ12.0 eV relative to the Fermi energy (EF; dashed line) First, Fig represents the total density of states (TDOS) of perovskites SrMO3 (M ¼ Mn and Co) along their cubic symmetry axes The large TDOS at EF in four methods suggest that two compounds have a metallic behavior, which is similar with the results obtained by LSDA method [30,32] There are some bands with different TDOS cross the EF in both spin-up and spin-down directions with no energy-gaps From GGA and GGA ỵ SOC, it is clearly seen that M Musa Saad H.-E / Journal of Science: Advanced Materials and Devices (2017) 115e122 117 Fig Crystal structure of perovskites AMO3 (a) The cubic unit cell, A-atoms (grey) at the corners, M-atoms (blue) in the centers and O-atoms (red) in the face-centers (b) The corner-sharing octahedral structure, where A-atoms occupy every void, which is created by eight MO6 octahedra, giving an 12-fold oxygen coordination for A-atoms and 6-fold oxygen coordination for M-atoms Table DFT calculations of the structural properties for SrMO3 (M ¼ Mn and Co) SrMO3 M ẳ Mn4ỵ M ẳ Co4ỵ Crystal structure Space-group Cubic Cubic Pm3m 3.806 55.134 0.670 Pm3m 3.740 52.319 0.650 1.033 1.051 1b (½, ½, ½) 1a (0, 0, 0) 3d (0, 0, ½) 1b (½, ½, ½) 1a (0, 0, 0) 3d (0, 0, ½) 2.6913 1.9030 90 180 2.6446 1.8700 90 180 Lattice constant a () Cell volume V (3) R4ỵ M () T Atomic sites and positions (x, y, z) Sr M O Bond distances and bond angles SreO (Å) MeO (Å) OeMeO ( ) MeOeM ( ) the TDOS split into three main bands, valence band, between À7.0 eV and À3.0 eV, conduction band through EF, between 3.0 eV and ỵ4.0 eV, and a band above the EF, between ỵ4.0 eV and ỵ11.0 eV In GGA ỵ U and GGA ỵ SOC ỵ U, Fig 2(c) and (d), these bands have more splitting due to the U energy The main contribution in the spin-up and spin-down TDOS of SrMO3 (M ¼ Mn and Co) in the valence bands, between À7.0 eV and À1.0 eV, is mainly due to the Sr (5s), Mn (3d)/Co (3d) and O (2p) states The broad O (2p) bands between À3.0 eV and À6.0 eV can be seen to have almost identical structure in SrMnO3 and SrCoO3, as the 3d bands, which lie above them In addition, both bands of Mn (3d) in SrMnO3 and Co (3d) in SrCoO3 occupy the same energy levels As is well known, SOC is the relativistic effect and as such increases strongly with the nuclear charge of atoms containing partially filled bands [25] In 3d perovskites SrMO3 (M ¼ Mn and Co), since they contain atoms with a low nucleus charge, Z ¼ 25 for Mn (3d) and Z ¼ 27 for Co (3d), the effect of SOC is regularly small compared with the effect of correlation energy U, whereas, for 5d perovskites containing heavier atoms with a high nucleus charge, such as Z ¼ 75 for Re (5d), Z ¼ 76 for Os (5d) and Z ¼ 77 for Ir (5d), the SOC effect is much larger The 3d localized electrons in Mn (3d3) and Co (3d5) have less extended electronic orbitals in the valence bands, leading to significant increases in the electronic correlations and decreases in orbital overlap in the crystal structures Moreover, to explain the contribution of different states to the TDOS, the partial density of states (PDOS) of Sr (5s), Mn (3d)/Co (3d) and O (2p) in SrMO3 with M ¼ Mn and M ¼ Co are calculated and shows in Figs and 4, respectively From the GGA and GGA ỵ SOC for SrMnO3 in Figs and 4(a) and (b), the broad O (2p) bands between À2.5 eV and À7.0 eV can be seen with the Mn (3d) and Co (3d) bands above them, which they must place at the turn of the EF Two sharp spin-up and spin-down peaks of 3.26 and 2.79 expand from 1.20 eV to ỵ0.50 and from 0.92 eV to ỵ0.74 corresponding to the Mn (3d) and Co (3d) states, respectively, are clearly visible through EF Whereas, these peaks split in spin-up for M ¼ Mn and spin-down for M ¼ Co and decline to 2.77 and 0.90, respectively, in PDOS from GGA ỵ U and GGA ỵ SOC ỵ U methods, Figs and 4(c) and (d) Moreover, in all PDOS there is an electronic hybridization between M (3d)/Co (3d) and O (2p) bands, which is expected to be occurred between 2.0 eV and ỵ2.0 eV, and of course leads to the DE interaction in magnetic perovskites Once more, the Sr (5s) bands can be seen to have considerable dispersion suggesting that it is involved in covalent bonding, and the Mn (3d) and Co (3d) bands overlap with tiny orbitals of partially occupied Sr (5s) states The large TDOS at the EF suggests that the cubic FM structure is stable, and that a lower energy structure could be achieved by allowing spin-polarization of the conduction-electron The TDOS and PDOS of SrMnO3 are similar to that previously published [33e35], and agree well with the experiment [28,36] The top of the valence bands is composed of O (2p)eMn (3d) and O (2p)eCo (3d) hybridized orbitals, while the bottom of the conduction bands is mainly composed of Mn (3d) and Co (3d) orbitals, Figs and The modest contributions of Sr (5s) orbitals are located in the middle of the top of valence bottom of the conduction bands For SrMnO3, the calculated energy-gap in spin-down band is 0.52 eV, Fig 3, which compares well with the reported value, i.e 0.75 eV [34] The underestimation with respect to the experimental values 3.2e3.4 eV [28,36] is a well-known consequence of the incomplete cancellation of the selfinteraction in the local exchange functional of GGA Moreover, similar calculations are repeated by using the GGA ỵ U and GGA ỵ SOC ỵ U methods for SrMO3 (M ¼ Mn and Co) However, the energy-gap is only considerably changed with respect to the GGA 118 M Musa Saad H.-E / Journal of Science: Advanced Materials and Devices (2017) 115e122 Fig Total density of states (TDOS) for the perovskites SrMO3 (M ẳ Mn4ỵ and Co4ỵ), computed within DFT using (a) GGA, (b) GGA ỵ SOC, (c) GGA þ U and (d) GGA þ SOC þ U The horizontal solid lines indicate the zero TDOS and the vertical dashed lines indicate the Fermi level (EF) and GGA ỵ SOC methods, the energy-gap is 4.51 eV for M ¼ Mn, which is significantly increased, while for M ¼ Co, there is a tiny spin-up band cross the EF and two splitting spin-down bands around the EF Co results in SrCoO3 agreement with the previous results [37,38] In addition, no significant changes appear in the TDOS and PDOS shapes for SrMO3 compounds Furthermore, clearly, the PDOS for Mn (3d) and Co (3d) states are expanded and responsible for the metallic behavior of the perovskites SrMnO3 and SrCoO3, respectively Since the 3d orbitals split into t2g and eg states, the 3d-t2g states are more localized than the 3deg states Thus, the M (3d-eg)eO (2p) bond in SrMnO3 is stronger as compared with the M (3d-t2g)eO (2p) Consequently, the partial states of M (3d-eg) and O (2p) hybridize and cross the EF in the electronic TDOS, due to which the perovskites show metallic behavior It is also clear that M (3d-t2g) and M (3d-eg) in GGA ỵ U and GGA ỵ SOC þ U results, Figs and 4(c) and (d), are shifted toward the valence bands as compared to GGA and GGA ỵ SOC, which is due to the fact that GGA method is not appropriate to treat 3d states exactly 3.3 Magnetic properties In order to describe the magnetic properties of transition-metal perovskites, we first investigate the magnetic interaction and its mechanisms in SrMO3 (M ¼ Mn and Co) As is well known, DE is a type of a magnetic interaction that was originally proposed by C Zener [39] for FM manganites with perovskite structure Then it applied to SrMO3 by K Kubo and N Ohata [40] to account for the simultaneous appearance of its FM order and metallic behavior To describe DE mechanism in perovskites SrMO3, a little must be first understood about the electronic and magnetic structures about the transition-metals Mn (3d) and Co (3d) sites In an ideal crystal lattice, the 3d orbital splits into two sub-states, a triple t2g and double eg sub-orbitals, due to the crystal field created by the cubic symmetry surrounding the M (3d) sites with Mn4ỵ (3d3; t32g e0g ) and Co4ỵ (3d5; t32g e2g ) The doublet eg sub-orbitals in SrMO3 usually lie 2e4 eV above the triplet t2g sub-orbitals in energy, see Fig M Musa Saad H.-E / Journal of Science: Advanced Materials and Devices (2017) 115e122 119 Fig Total and partial [Sr (5s), Mn (3d) and O (2p)] density of states of SrMnO3, computed within DFT using (a) GGA, (b) GGA ỵ SOC, (c) GGA ỵ U and (d) GGA ỵ SOC ỵ U The vertical dashed lines indicate the Fermi level (EF) In octahedral crystal eld, Mn4ỵ (3d3) ions have only one possible spin state, t32g e0g (S ¼ 3/2) with three unpaired electrons, whereas Co4ỵ (3d5) ions have three possible spin states, t52g e0g (S ¼ 1/2), t42g e1g (S ¼ 3/2) and t32g e2g (S ¼ 5/2) with one, three and five unpaired electrons, respectively We designated these spin states in Fig as low spin (LS) state with one unpaired electron, intermediate spin (IS) state with two or three unpaired electrons and high spin (HS) state with ve unpaired electrons for Mn4ỵ and Co4ỵ ions These spin congurations of Mn4ỵ (3d3) and Co4ỵ (3d5) ions in octahedral crystal eld are schematically represented in Fig Moreover, the Coulomb-repulsion energy U forces each 3delectron to lay on a lonely level, and the Hund's rule coupling is strong enough to ensure that all the 3d electrons on the Mn (3d) and Co (3d) sites are FM aligned In Mn (3d) ions, three electrons drive to fill the lower lying t32g states forming and inert core-spin of S ¼ 3/2, whereas the remaining electrons lie in a superposition of the e 0g states While in Co (3d) ions also three electrons drive to fill the t32g states forming S ¼ 3/2 and the remaining electrons lie in the e2g states These electrons may move through the lattice subject to the constraint that the hopping-electron always has its spin aligned with its host's core-spin The hopping from Mn4ỵ to Mn3ỵ or Co4ỵ to Co3ỵ is mediated by the O2À ions between them, and DE organizes this hopping interaction As the temperature is lowered and spin fluctuations decreased, the crystal lowers its energy by FM aligning the M (3d) core-spins allowing the eg electrons to gain kinetic energy and move about the crystal The hopping transfer integral calculated from such DE theory is a very sensitive function of the M4ỵeOeM3ỵ bond angle, deviated from the ideal 180 resulting in much reduced hopping probability This agrees with experimental evidence, where different divalent dopants with different atomic radii cause about large change in the Curie temperature (TC) Dopants with small atomic radii cause a buckling in the M4ỵeOeM3ỵ bond angle, decreasing the single electron bandwidth and consequently reducing the TC The effect of dopant size on the structural and electronic properties can be described using the tolerance factor, which describes the degree of deviation from ideal cubic symmetry, as it discussed extensively in Section 3.1 for crystal structure properties Then, the magnetic properties of perovskites SrMO3 (M ¼ Mn and Co) were investigated in detail, where the spin magnetic moments were calculated by using the four different approximations: GGA, GGA ỵ SOC, GGA ỵ U and GGA ỵ SOC þ U, within DFT method 120 M Musa Saad H.-E / Journal of Science: Advanced Materials and Devices (2017) 115e122 Fig Total and partial [Sr (5s), Co (3d) and O (2p)] density of states of SrCoO3, computed within DFT using (a) GGA, (b) GGA ỵ SOC, (c) GGA þ U and (d) GGA þ SOC þ U The vertical dashed lines indicate the Fermi level (EF) Fig Splitting of 3d levels into t2g and eg states due to the octahedral crystal field and different possible spin states for (a) Mn4ỵ (3d3) and (b) Co4ỵ (3d3) in SrMO3 (M ¼ Mn and Co) M Musa Saad H.-E / Journal of Science: Advanced Materials and Devices (2017) 115e122 Table Spin magnetic moments (in mB) in cubic SrMO3 (M ẳ Mn and Co), calculated using GGA, GGA ỵ SOC, GGA ỵ U and GGA ỵ SOC ỵ U within DFT method DFT method SrMnO3 Sr (5s) Mn (3d) O (2p) Total SrCoO3 Sr (5s) Co (3d) O (2p) Total GGA GGA ỵ SOC GGA ỵ U GGA ỵ SOC ỵ U 0.0669 2.4768 0.3037 2.6450 0.0669 2.4768 0.3037 2.6451 0.0251 3.6688 À0.7828 3.4330 0.0251 3.6688 À0.7828 3.4330 0.0589 1.6519 0.5422 2.2530 0.0590 1.6523 0.5430 2.2543 0.0593 3.4630 1.0808 3.8826 0.0593 3.4629 1.0809 3.8825 Table shows the calculated partial and total spin magnetic moments for the cubic symmetry in two compounds First, it is remarked that when the Coulomb repulsion-energy U was used, the obtained spin magnetic moments have an extensive increase, whereas the SOC term has a small effect since the partially filled 3d states in Mn and Co ions are weak in their compounds It is seen from these results, the spin magnetic moments are overestimated by both GGA ỵ U and GGA ỵ SOC ỵ U methods, but less that the GGA ỵ U calculation gives the biggest values, especially the partial spin magnetic moments of Mn (3d) and Co (3d) ions, which are more important than others The electronic configuration of the Mn (Z ¼ 25) and Co (Z ¼ 27) atoms are [Ar]18 3d5 4s2 and [Ar]18 3d7 4s2, respectively, which indicate the dissimilar configurations of these elements in their compounds The obtained values are 3.6688 mB for M ¼ Mn (3d) and 3.4630 mB for M ¼ Co (3d), which suggest the electronic conguration of the 3d ions in-between Mn4ỵ (3d3) and Mn3ỵ (3d4), and Co4ỵ (3d5) and Co3ỵ (3d6) states in SrMnO3 and SrCoO3, respectively These results agree well with the partial and total spin magnetic moments of SrMnO3 and SrCoO3 calculated using the GGA method [16,31,41] In those studies, it carried out the values of 2.50 mB and 2.967 mB, respectively, for the FM configuration of the cubic structures On the other hand, the spin magnetic moment of the O2À ions is very small; approximately equal to zero in two compounds, with small contribution to the total spin magnetic moment The same remark is revealed for the Sr2ỵ ions, and found that its spin magnetic moment is negligibly smaller than the other ions in each of SrMnO3 and SrCoO3 Moreover, both GGA and GGA ỵ SOC calculations produce similar results for the M (3d) ions, around 2.5 mB and 1.7 mB for M ¼ Mn and for M ¼ Co, respectively, whereas the GGA ỵ U and GGA ỵ SOC þ U calculations overestimated the spin magnetic moment of the M (3d) ions, in comparison with the obtained values from GGA and GGA ỵ SOC The GGA ỵ U and GGA ỵ SOC ỵ U calculations give bigger values than GGA and GGA ỵ SOC ones, which show the effect of U parameter, especially on the spin magnetic moment of the M (3d) ions Thus, the exchange-correlation methods, GGA ỵ U and GGA ỵ SOC ỵ U, are more accurate than others used in the calculations, which they will be indispensable for the electronic and magnetic structure calculations, particularly for the transition-metal materials Conclusion The structural, electronic and magnetic properties of two interested transition-metal perovskites SrMO3 (M ¼ Mn and Co) were investigated via the full potential linear muffin-tin orbital (FPLMTO) method within generalized gradient approximation (GGA) and GGA þ U based on the density functional theory (DFT) First, the structural properties of SrMO3 perovskites were investigated; two compounds crystallize in a cubic symmetry with space group of 121 Pm3m (no 221) The increasing of occupation-number on M-site in perovskites SrMO3 (M ẳ Mn4ỵ and Co4ỵ) decreased the lattice constant and the unit cell volume, and increased the tolerance factor of SrMO3 Then the electronic properties of perovskites SrMO3 (M ¼ Mn and Co) are also investigated by calculating the total (TDOS) and partial (PDOS) density of states In electronic TDOS, there are some bands with different DOS cross the EF in both of the spin-up and spin-down directions We found that the PDOS of Mn (3d) and Co (3d) states, which hybridize with O (2p) states, are responsible for the metallic behavior of the perovskites SrMnO3 and SrCoO3, respectively Finally, the magnetic properties of transition-metal perovskites SrMO3 (M ẳ Mn4ỵ and Co4ỵ) were studied in detail Also, the possible spin states of Mn4ỵ (3d3) and Co4ỵ (3d5) ions in octahedral crystal eld were discussed, where Mn4ỵ (3d3) splitting into t32g e0g (S ¼ 3/2) with three unpaired electrons, whereas Co4ỵ (3d5) states have t52g e0g (S ẳ 1/2), t42g e1g (S ¼ 3/2) and t32g e2g (S ¼ 5/2) with one, three and five unpaired electrons, respectively The magnetic double-exchange interaction M4ỵeOeM3ỵ and its mechanisms in SrMO3 were described The partial and total spin magnetic moments for the cubic symmetry in SrMO3 (M ẳ Mn4ỵ and Co4ỵ) were determined by using the above mentioned four different approximations, within the DFT method Acknowledgments The author gratefully acknowledges Deanship of Scientific Research, Qassim University, Saudi Arabia for financial support of this research study (Grant number 3000) References [1] F.F Fava, P D'Arco, R Orlando, R Dovesi, A quantum-mechanical investigation of the electronic and magnetic-properties of CaMnO3 perovskite, J 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transition-metal materials Conclusion The structural, electronic and magnetic properties of two interested transition-metal perovskites SrMO3 (M ¼ Mn and Co) were investigated via the full... mainly composed of Mn (3d) and Co (3d) orbitals, Figs and The modest contributions of Sr (5s) orbitals are located in the middle of the top of valence bottom of the conduction bands For SrMnO3,... interaction M4 ỵeOeM3ỵ and its mechanisms in SrMO3 were described The partial and total spin magnetic moments for the cubic symmetry in SrMO3 (M ¼ Mn4 ỵ and Co4 ỵ) were determined by using the above mentioned