- Email: [email protected]
(InN)1 superlattices
Superlattices and Microstructures 53 (2013) 16–23
Contents lists available at SciVerse ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
Magnetic behavior of (MnN)1/(AlN)1, (MnN)1/(GaN)1, and (MnN)1/(InN)1 superlattices H. Heddar a, A. Zaoui b,⇑, M. Ferhat a a
Département de Physique, Université des Sciences et de la Technologie d’Oran, USTO, Oran, Algeria LGCgE (EA 4515), Ecole Polytechnique de Lille, Université des Sciences et de la Technologie de Lille, Cité Scientifique, Avenue Paul Langevin, 59655 Villeneuve D’Ascq Cedex, France b
a r t i c l e
i n f o
Article history: Received 5 August 2012 Received in revised form 16 September 2012 Accepted 22 September 2012 Available online 13 October 2012 Keywords: Magnetism MnN/AlN MnN/GaN MnN/InN Heterostructures
a b s t r a c t Using density functional theory, we have studied the electronic and magnetic properties of zinc blende (MnN)1/(AlN)1, (MnN)1/ (GaN)1, and (MnN)1/(InN)1 superlattice in the (0 0 1) direction. We demonstrate the possibility to obtain half-metallic ferromagnets in (MnN)1/(GaN)1, and (MnN)1/(InN)1 and (MnN)1/(AlN)1 with a total magnetic moment close to 8lB. The analysis of the partial density of states reveals that ferromagnetism can be explained by the strong p–d hybridization of N and Mn atoms. The magnetism comes essentially from the d orbitals of Mn atoms, and to less extent from the interstitial region. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The strong interest in spin based electronic as promising materials for innovative spin-based devices is motivating studies in many related materials. This has been motivated by the prospect of using spin in addition, or as an alternative, to charge as the physical-quantity-carrying information, which may change device functionality and paving the way to a new field called spintronic. Of particular interest are half-metallic ferromagnets (HMF). HMF are materials showing spin ferromagnetism, but with the exotic property of presenting a metallic density of states only for the one spin direction, in parallel with a clear band gap around the Fermi level for the other spin channel. Therefore, the above state may show nearly 100% spin polarization and can thus be used as spin injectors for magnetic random access memories and other spin-dependent devices.
⇑ Corresponding author. E-mail address: [email protected] (A. Zaoui). 0749-6036/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.spmi.2012.09.011
H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
17
On the other hand, recent progress in thin-film deposition techniques, such as molecular beam epitaxy (MBE) and the ability to control the growth of semiconductors crystals has open the door to the fabrication of high-quality artificial superlattice of many different geometries and semiconductors classes. The compounds are new artificial materials formed by the repeated growth of a pattern made of layers of semiconductors with different numbers of layers and compositions. Electrons in these atomic systems usually encounter interactions different from what they would encounter in natural crystals. Particularly these new materials exhibit new physical properties, unknown from the bulk shape of the constituents. Since de Groot et al. [1] discovery in 1983, many HFMs have been theoretically predicted and some of them have been confirmed experimentally such as zinc-blende CrAs [2], CrSb [3], and MnAs [4], diluted magnetic semiconductors such as Mn doped InAs [5], Mn doped GaAs [6], and Cr doped BeTe [7] or ZnTe [8], and more recently non-magnetic metal copper (Cu) doped ZnO [9–10]. Although many transition-metal doped III–V or II–VI compounds with zinc-blende structure have been studied extensively, it is desirable to explore new HFMs compounds, compatible with important III–V and II–VI semiconductors. We attempt to achieve here good compatibility both in crystal and electronic structures. This compatibility should be useful to fabricate stable compounds and to design devices inheriting the achievement of current semiconductors technology. In this context an alternative approach to polarize the spin of carriers in semiconductors is to use magnetic multi layers and superlattices. The superlattices of MnN and XN (X = Al, Ga, and In) would be
Fig. 1. Total energy as function of volume for the FM phases of (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 superlattice.
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H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23 Table 1 Calculated lattice constants a, bulk moduli B, and the pressure derivative B’ of the (MnN)1/(XN)1 (X = Al, Ga, In) superlattice. Superlattice
a (Å)
B (GPa)
B0
(MnN)1/(AlN)1 (MnN)1/(GaN)1 (MnN)1/(InN)1
4.439 4.565 4.851
141.41 158.08 134.43
4.840 2.026 3.641
Fig. 2. Band structure of (MnN)1/(AlN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 3. Band structure of (MnN)1/(GaN)1 (0 0 1) for spin-up (a) and spin-down (b).
H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
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a good candidates, since Mn such a dopant for XN has attracted great attention, both theoretically [11– 16] and experimentally [17–23]. The propose of the present work is to explore a new HMF-layered materials based on zinc-blende structure, namely (MnN)1/(AlN)1, (MnN)1/GaN)1, and (MnN)1/(InN)1, using full potential linearized augmented plane waves (FP-LAPW) method. The rest of the paper is organized as follows: in section 2, we briefly describe the computational techniques used in this work. Results and discussions will be presented in section 3. Finally, the conclusion will be given in section 4. 2. Method The calculations were performed in the framework of the density functional theory. We have employed the full potential linearized augmented plane wave (FLAPW) method as implemented in the WIEN2k code [24]. The exchange and correlation effects were treated using the generalized gradient approximation GGA [25], which is supposed to be ‘superior’ for magnetic properties. The
Fig. 4. Band structure of (MnN)1/(InN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 5. Total density of states of (MnN)1/(AlN)1 (0 0 1) for spin-up (a) and spin-down (b).
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H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
muffin-tin radii (RMT) of Mn, Al, Ga, In and N were chosen to be 1.80 au, 1.68 au, 1.80 au, 1.82 au and 1.56 au respectively. We expand the basis function up to RMT KMAX = 8 (RMT is the plane wave radius; KMAX is the maximum modulus for the reciprocal lattice vector). Brillouin zone integrations were performed with the special k-point method over a 4 4 4 Monkhorst–Pack mesh [26]. To simulate (MnN)1/(XN)1 in the (0 0 1) direction, cubic supercells containing 8 atoms are employed. Full atomic relaxation was performed with a numerical threshold of 0.5 mRy/cell for total energy calculations. 3. Results and discussions Fig. 1 shows the total energy of (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 for the ferromagnetic states (FM). The calculated total energies are fitted with the Murnaghan’s equation of states [27] (also see Refs. [28–31] for additional evidence). The optimized structural parameters (the lattice parameters a, the bulk modulus B, its pressure derivative B’) for (MnN)1/(XN)1 superlattices are given in Table 1. The calculated band structures of (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 in their FM state phases are shown respectively in Figs. 2–4. It is clear that (MnN)1/(AlN)1 does not show
Fig. 6. Total density of states of (MnN)1/(GaN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 7. Total density of states of (MnN)1/(InN)1 (0 0 1) for spin-up (a) and spin-down (b).
H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
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Fig. 8. Partial density of states of (MnN)1/(AlN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 9. Partial density of states of (MnN)1/(GaN)1 (0 0 1) for spin-up (a) and spin-down (b).
half-metallicity (i.e., valence and conduction bands cross the Fermi level). However (MnN)1/(GaN)1 and (MnN)1/(InN)1 are half-metallic ferromagnets, since the majority spin (spin-up, MAS) is metallic, and the minority spin (spin-down, MIS) is semiconducting. The 100% polarization of conduction carriers, which is required in spin injection, suggest that it can be used efficiently for injection of spin polarized charge carriers into (MnN)1/(GaN)1 (0 0 1) and (MnN)1/(InN)1 (0 0 1) superlattices. Figs. 5–7 represent respectively total density of states (TDOS) of spin up and spin down for (MnN)1/ (AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 respectively. The TDOS for the (MnN)1/(XN)1, confirm the results found in band structure calculations. (MnN)1/(GaN)1 and (MnN)1/(InN)1 are found HFM, where
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H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
Fig. 10. Partial density of states of (MnN)1/(InN)1 (0 0 1) for spin-up (a) and spin-down (b).
the spin-up channel is completely occupied and the spin-down channel is completely empty; while for (MnN)1/(AlN)1 all spin channels are empty, since there is a finite DOS at Fermi level for majority and minority spin. In order to analyze the bonding properties in detail, orbital projected density of states (PDOS) are needed. PDOS of spin-up and spin-down for (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 are given respectively in Figs. 8–10. The lowest bands for (MnN)1/(AlN)1 at 15 eV for MAS and MIS are essentially isolated N s states; while the N-s states are composed of two peaks at 16 eV and at 13 eV for (MnN)1/(GaN)1 and (MnN)1/(InN)1 for both spin channels. Furthermore (MnN)1/(GaN)1 and (MnN)1/(InN)1 are characterized by the presence of a strong localized Ga–d and In–d states at 15 eV for both spin channels. The upper valence band for the (MnN)1/(XN)1 compounds is dominated by the Mn d and N p orbitals, which differ widely for spin-up and spin-down. For the MAS, the valence band between 8 eV and Fermi level (Ef) comes mainly from the Mn d and N p states, reflecting the bonding t2g–p states. This suggests that the hybridization between Mn d and N p orbital is responsible for the half-metallic behaviour of (MnN)1/(GaN)1 and (MnN)1/(InN)1 superlattices. The conduction band originates principally from N p and X s and p states. For the spin-down channel, the valence band between 7 and Table 2 Calculated total magnetic moments (lB) and atomic magnetic moments of Al, Ga, In, N, and Mn in the (MnN)1/(XN)1 (X = Al, Ga, In) superlattice. (MnN)1/(AlN)1
lB
(MnN)1/(GaN)1
lB
(MnN)1/(InN)1
lB
Interstitialregion Al(1) Al(2) Mn(3) Mn(4) N(5) N(6) N(7) N(8) Total
1.588 0.028 0.028 3.094 3.085 0.031 0.03 0.036 0.036 7.96
Interstitial region Ga(1) Ga(2) Mn(3) Mn(4) N(5) N(6) N(7) N(8) Total
1.363 0.04 0.04 3.264 3.264 0.006 0.006 0.007 0.006 8
Interstitial region In(1) In(2) Mn(3) Mn(4) N(5) N(6) N(7) N(8) Total
1.417 0.024 0.024 3.293 3.271 0.006 0.006 0.008 0.007 8
H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
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3 eV originate principally from the N p states, with a weak participation of the Mn d states; while for the conduction band, we notice the strong dominance of the empty nonbonding Mn d states. Now, we turn to the magnetic properties of the (MnN)1/(XN)1 compounds. In Table 2, we give the total and local magnetic moments for all compounds. The calculated total magnetic moments are respectively 7.96lB, 8lB, and 8lB for (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1. One property of half-metallic materials is that the total magnetic moments should exhibit integer spin moments, which is confirmed in all our calculated half-metallic systems. In conjunction with the band structure and DOS calculations, it would suggest that the interaction between the N p and Mn d states preserves the total integer moments of (MnN)1/(GaN)1 and (MnN)1/(InN)1. From Table 2, it is clear that the total magnetic moment for all compounds is mainly due to the Mn atom, and to less extent to the interstitial region; while the contribution of the X and N atoms are insignificant. 4. Conclusion We have study the electronic and magnetic properties of (MnN)1/(XN)1 (0 0 1) (X = Al, Ga, In) superlattices, using first-principles full potential linearized augmented plane waves (FP-LAPW) method. The main result to underline is that (MnN)1/(GaN)1 and (MnN)1/(InN)1 are half-metallic ferromagnets with a total magnetic moment of 8lB; while (MnN)1/(AlN)1 is found metallic for both spin channels with a total magnetic moment of 7.96lB. The Mn atoms are found to be the main source for (MnN)1/(GaN)1 and (MnN)1/(InN)1. The magnetism comes essentially from the Mn atom and to less extent to the interstitial region. However the contributions of Al, Ga, In and N atoms are quite insignificant. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]
[25] [26] [27] [28] [29] [30] [31]
R.A. de Groot, F.M. Mueller, P.G. van Engen, K.H. Buschow, Phys. Rev. Lett. 50 (1983) 2024. H. Akinaga, T. Manago, M. Shirai, Jpn. J. Appl. Phys. 39 (Part 2) (2000) L1118. J.H. Zhao, F. Matsukura, K. Takamura, E. Abe, D. Chiba, H. Ohno, Appl. Phys. Lett. 79 (2001) 2776. K. Ono, J. Okabayashi, M. Mizuguchi, M. Oshima, A. Fujimori, H. Akinaga, J. Appl. Phys. 91 (2002) 8088. H. Ohno, H. Munekata, T. Penney, S. von Molenár, L.L. Chang, Phys. Rev. Lett. 68 (1992) 2664. H. Ohno, A. Shen, F. Matuskura, A. Oiwa, A. Endo, S. Katsumoto, Y. Iye, Appl. Phys. Lett. 69 (1996) 363. Ko Viloane, M.G. Speenivasan, K.L. Teo, T. Liew, T.C. Chong, J. Appl. Phys. 99 (1996) 08D514. H. Saito, V. Zayets, S. Yamagata, K. Ando, Phys. Rev. Lett. 90 (2003) 207202. C. Sudakar, K. Padmanabhan, R. Naik, G. Lawes, B.J. Kriby, S. Kumar, V.M. Naik, Appl. Phys. Lett. 93 (2008) 042502. M. Ferhat, A. Zaoui, R. Ahuja, Appl. Phys. Lett. 94 (2009) 142502. T. Dietl, H. Ohno, F. Matsukura, J. Cibert, D. Ferrand, Science 287 (2000) 1019. G.P. Das, B.K. Rao, P. Jena, Phys. Rev. B 68 (2003) 035207. K. Sato, W. Schweika, P.H. Dederichs, H. Katayama-Yoshida, Phys. Rev. B 70 (2004) 201202(R). P. Mahadevan, S. Mahallakshmi, Phys. Rev. B 73 (2006) 153201. J.A. Chen, J.Z. Liu, H. Raebiger, S. Lany, A. Zunger, Phys. Rev. B 78 (2008) 184109. C. Caetano, M. Marques, L.G. Ferreira, L.K. Teles, Appl. Phys. Lett. 94 (2009) 241914. M. Reed, N. El-Masry, H. Stadelmaier, M. Ritums, C. Parker, J. Roberts, S. Bedair, Appl. Phys. Lett. 79 (2001) 3473. S. Dhar, O. Brandt, A. Trampert, L. Däweritz, K.J. Friedland, K.H. Ploog, J. Keller, B. Beschoten, G. Güntherodt, Appl. Phys. Lett. 82 (2003) 2077. S. Sonada, S. Shimizu, T. Sasaki, Y. Yamamoto, H. Hori, J. Crys, Growth 237 (2002) 1358. V.A. Chitta, J.A. Coaquira, J.R. Fernandez, C.A. Duarte, J.R. Leite, D. Schikora, D.J. As, K. Lischka, E. Abram, Appl. Phys. Lett. 85 (2004) 3777. S. Granville, B.J. Ruke, A.R.H. Preston, T. Stewart, F. Budde, H.J. Trodahl, A. Bittar, J.E. Downes, M. Ridgway, J. Appl. Phys. 104 (2008) 103710. P.P. Chen, H. Makino, T. Yao, Solid State Commun. 130 (2004) 25. R. Frazier, G. Thaler, M. Overberg, B. Gila, C.R. Abernathy, S. Pearton, J. Appl. Phys. 83 (2003) 1758. P. Blaha, K. Schwarz, J. Luitz, WIEN2k, Vienna, University of Technology 1997 (improved and updated Unix version of the original copyrighted Wien code, witch was published by P. Blaha, K. Schwarz, P. Sorantin, S.B. Trickey, Comput. Phys. Commun. 59 (1990) 399. J.P. Perdew, K. Burke, M. Ernzerhof, Phys. Rev. Lett. 77 (1996) 3865. J. Monkhorst, J.D. Pack, Phys. Rev. B 13 (1976) 5188. F.D. Murnaghan, Proc. Natl. Acad. Sci. USA 30 (1944) 244. M. Ferhat, A. Zaoui, M. Certier, B. Khelifa, Phys. Lett. A 216 (1996) 187. M. Ferhat, A. Zaoui, Infrared Phys. & Tech. 42 (2001) 81. M. Ferhat, A. Zaoui, Appl. Phys. Lett. 88 (2006) 161902. A. Belabbes, M. Ferhat, A. Zaoui, Appl. Phys. Lett. 88 (2006) 152109.
Contents lists available at SciVerse ScienceDirect
Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices
Magnetic behavior of (MnN)1/(AlN)1, (MnN)1/(GaN)1, and (MnN)1/(InN)1 superlattices H. Heddar a, A. Zaoui b,⇑, M. Ferhat a a
Département de Physique, Université des Sciences et de la Technologie d’Oran, USTO, Oran, Algeria LGCgE (EA 4515), Ecole Polytechnique de Lille, Université des Sciences et de la Technologie de Lille, Cité Scientifique, Avenue Paul Langevin, 59655 Villeneuve D’Ascq Cedex, France b
a r t i c l e
i n f o
Article history: Received 5 August 2012 Received in revised form 16 September 2012 Accepted 22 September 2012 Available online 13 October 2012 Keywords: Magnetism MnN/AlN MnN/GaN MnN/InN Heterostructures
a b s t r a c t Using density functional theory, we have studied the electronic and magnetic properties of zinc blende (MnN)1/(AlN)1, (MnN)1/ (GaN)1, and (MnN)1/(InN)1 superlattice in the (0 0 1) direction. We demonstrate the possibility to obtain half-metallic ferromagnets in (MnN)1/(GaN)1, and (MnN)1/(InN)1 and (MnN)1/(AlN)1 with a total magnetic moment close to 8lB. The analysis of the partial density of states reveals that ferromagnetism can be explained by the strong p–d hybridization of N and Mn atoms. The magnetism comes essentially from the d orbitals of Mn atoms, and to less extent from the interstitial region. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction The strong interest in spin based electronic as promising materials for innovative spin-based devices is motivating studies in many related materials. This has been motivated by the prospect of using spin in addition, or as an alternative, to charge as the physical-quantity-carrying information, which may change device functionality and paving the way to a new field called spintronic. Of particular interest are half-metallic ferromagnets (HMF). HMF are materials showing spin ferromagnetism, but with the exotic property of presenting a metallic density of states only for the one spin direction, in parallel with a clear band gap around the Fermi level for the other spin channel. Therefore, the above state may show nearly 100% spin polarization and can thus be used as spin injectors for magnetic random access memories and other spin-dependent devices.
⇑ Corresponding author. E-mail address: [email protected] (A. Zaoui). 0749-6036/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.spmi.2012.09.011
H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
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On the other hand, recent progress in thin-film deposition techniques, such as molecular beam epitaxy (MBE) and the ability to control the growth of semiconductors crystals has open the door to the fabrication of high-quality artificial superlattice of many different geometries and semiconductors classes. The compounds are new artificial materials formed by the repeated growth of a pattern made of layers of semiconductors with different numbers of layers and compositions. Electrons in these atomic systems usually encounter interactions different from what they would encounter in natural crystals. Particularly these new materials exhibit new physical properties, unknown from the bulk shape of the constituents. Since de Groot et al. [1] discovery in 1983, many HFMs have been theoretically predicted and some of them have been confirmed experimentally such as zinc-blende CrAs [2], CrSb [3], and MnAs [4], diluted magnetic semiconductors such as Mn doped InAs [5], Mn doped GaAs [6], and Cr doped BeTe [7] or ZnTe [8], and more recently non-magnetic metal copper (Cu) doped ZnO [9–10]. Although many transition-metal doped III–V or II–VI compounds with zinc-blende structure have been studied extensively, it is desirable to explore new HFMs compounds, compatible with important III–V and II–VI semiconductors. We attempt to achieve here good compatibility both in crystal and electronic structures. This compatibility should be useful to fabricate stable compounds and to design devices inheriting the achievement of current semiconductors technology. In this context an alternative approach to polarize the spin of carriers in semiconductors is to use magnetic multi layers and superlattices. The superlattices of MnN and XN (X = Al, Ga, and In) would be
Fig. 1. Total energy as function of volume for the FM phases of (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 superlattice.
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H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23 Table 1 Calculated lattice constants a, bulk moduli B, and the pressure derivative B’ of the (MnN)1/(XN)1 (X = Al, Ga, In) superlattice. Superlattice
a (Å)
B (GPa)
B0
(MnN)1/(AlN)1 (MnN)1/(GaN)1 (MnN)1/(InN)1
4.439 4.565 4.851
141.41 158.08 134.43
4.840 2.026 3.641
Fig. 2. Band structure of (MnN)1/(AlN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 3. Band structure of (MnN)1/(GaN)1 (0 0 1) for spin-up (a) and spin-down (b).
H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
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a good candidates, since Mn such a dopant for XN has attracted great attention, both theoretically [11– 16] and experimentally [17–23]. The propose of the present work is to explore a new HMF-layered materials based on zinc-blende structure, namely (MnN)1/(AlN)1, (MnN)1/GaN)1, and (MnN)1/(InN)1, using full potential linearized augmented plane waves (FP-LAPW) method. The rest of the paper is organized as follows: in section 2, we briefly describe the computational techniques used in this work. Results and discussions will be presented in section 3. Finally, the conclusion will be given in section 4. 2. Method The calculations were performed in the framework of the density functional theory. We have employed the full potential linearized augmented plane wave (FLAPW) method as implemented in the WIEN2k code [24]. The exchange and correlation effects were treated using the generalized gradient approximation GGA [25], which is supposed to be ‘superior’ for magnetic properties. The
Fig. 4. Band structure of (MnN)1/(InN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 5. Total density of states of (MnN)1/(AlN)1 (0 0 1) for spin-up (a) and spin-down (b).
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H. Heddar et al. / Superlattices and Microstructures 53 (2013) 16–23
muffin-tin radii (RMT) of Mn, Al, Ga, In and N were chosen to be 1.80 au, 1.68 au, 1.80 au, 1.82 au and 1.56 au respectively. We expand the basis function up to RMT KMAX = 8 (RMT is the plane wave radius; KMAX is the maximum modulus for the reciprocal lattice vector). Brillouin zone integrations were performed with the special k-point method over a 4 4 4 Monkhorst–Pack mesh [26]. To simulate (MnN)1/(XN)1 in the (0 0 1) direction, cubic supercells containing 8 atoms are employed. Full atomic relaxation was performed with a numerical threshold of 0.5 mRy/cell for total energy calculations. 3. Results and discussions Fig. 1 shows the total energy of (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 for the ferromagnetic states (FM). The calculated total energies are fitted with the Murnaghan’s equation of states [27] (also see Refs. [28–31] for additional evidence). The optimized structural parameters (the lattice parameters a, the bulk modulus B, its pressure derivative B’) for (MnN)1/(XN)1 superlattices are given in Table 1. The calculated band structures of (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 in their FM state phases are shown respectively in Figs. 2–4. It is clear that (MnN)1/(AlN)1 does not show
Fig. 6. Total density of states of (MnN)1/(GaN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 7. Total density of states of (MnN)1/(InN)1 (0 0 1) for spin-up (a) and spin-down (b).
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Fig. 8. Partial density of states of (MnN)1/(AlN)1 (0 0 1) for spin-up (a) and spin-down (b).
Fig. 9. Partial density of states of (MnN)1/(GaN)1 (0 0 1) for spin-up (a) and spin-down (b).
half-metallicity (i.e., valence and conduction bands cross the Fermi level). However (MnN)1/(GaN)1 and (MnN)1/(InN)1 are half-metallic ferromagnets, since the majority spin (spin-up, MAS) is metallic, and the minority spin (spin-down, MIS) is semiconducting. The 100% polarization of conduction carriers, which is required in spin injection, suggest that it can be used efficiently for injection of spin polarized charge carriers into (MnN)1/(GaN)1 (0 0 1) and (MnN)1/(InN)1 (0 0 1) superlattices. Figs. 5–7 represent respectively total density of states (TDOS) of spin up and spin down for (MnN)1/ (AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 respectively. The TDOS for the (MnN)1/(XN)1, confirm the results found in band structure calculations. (MnN)1/(GaN)1 and (MnN)1/(InN)1 are found HFM, where
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Fig. 10. Partial density of states of (MnN)1/(InN)1 (0 0 1) for spin-up (a) and spin-down (b).
the spin-up channel is completely occupied and the spin-down channel is completely empty; while for (MnN)1/(AlN)1 all spin channels are empty, since there is a finite DOS at Fermi level for majority and minority spin. In order to analyze the bonding properties in detail, orbital projected density of states (PDOS) are needed. PDOS of spin-up and spin-down for (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1 are given respectively in Figs. 8–10. The lowest bands for (MnN)1/(AlN)1 at 15 eV for MAS and MIS are essentially isolated N s states; while the N-s states are composed of two peaks at 16 eV and at 13 eV for (MnN)1/(GaN)1 and (MnN)1/(InN)1 for both spin channels. Furthermore (MnN)1/(GaN)1 and (MnN)1/(InN)1 are characterized by the presence of a strong localized Ga–d and In–d states at 15 eV for both spin channels. The upper valence band for the (MnN)1/(XN)1 compounds is dominated by the Mn d and N p orbitals, which differ widely for spin-up and spin-down. For the MAS, the valence band between 8 eV and Fermi level (Ef) comes mainly from the Mn d and N p states, reflecting the bonding t2g–p states. This suggests that the hybridization between Mn d and N p orbital is responsible for the half-metallic behaviour of (MnN)1/(GaN)1 and (MnN)1/(InN)1 superlattices. The conduction band originates principally from N p and X s and p states. For the spin-down channel, the valence band between 7 and Table 2 Calculated total magnetic moments (lB) and atomic magnetic moments of Al, Ga, In, N, and Mn in the (MnN)1/(XN)1 (X = Al, Ga, In) superlattice. (MnN)1/(AlN)1
lB
(MnN)1/(GaN)1
lB
(MnN)1/(InN)1
lB
Interstitialregion Al(1) Al(2) Mn(3) Mn(4) N(5) N(6) N(7) N(8) Total
1.588 0.028 0.028 3.094 3.085 0.031 0.03 0.036 0.036 7.96
Interstitial region Ga(1) Ga(2) Mn(3) Mn(4) N(5) N(6) N(7) N(8) Total
1.363 0.04 0.04 3.264 3.264 0.006 0.006 0.007 0.006 8
Interstitial region In(1) In(2) Mn(3) Mn(4) N(5) N(6) N(7) N(8) Total
1.417 0.024 0.024 3.293 3.271 0.006 0.006 0.008 0.007 8
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3 eV originate principally from the N p states, with a weak participation of the Mn d states; while for the conduction band, we notice the strong dominance of the empty nonbonding Mn d states. Now, we turn to the magnetic properties of the (MnN)1/(XN)1 compounds. In Table 2, we give the total and local magnetic moments for all compounds. The calculated total magnetic moments are respectively 7.96lB, 8lB, and 8lB for (MnN)1/(AlN)1, (MnN)1/(GaN)1 and (MnN)1/(InN)1. One property of half-metallic materials is that the total magnetic moments should exhibit integer spin moments, which is confirmed in all our calculated half-metallic systems. In conjunction with the band structure and DOS calculations, it would suggest that the interaction between the N p and Mn d states preserves the total integer moments of (MnN)1/(GaN)1 and (MnN)1/(InN)1. From Table 2, it is clear that the total magnetic moment for all compounds is mainly due to the Mn atom, and to less extent to the interstitial region; while the contribution of the X and N atoms are insignificant. 4. Conclusion We have study the electronic and magnetic properties of (MnN)1/(XN)1 (0 0 1) (X = Al, Ga, In) superlattices, using first-principles full potential linearized augmented plane waves (FP-LAPW) method. The main result to underline is that (MnN)1/(GaN)1 and (MnN)1/(InN)1 are half-metallic ferromagnets with a total magnetic moment of 8lB; while (MnN)1/(AlN)1 is found metallic for both spin channels with a total magnetic moment of 7.96lB. The Mn atoms are found to be the main source for (MnN)1/(GaN)1 and (MnN)1/(InN)1. The magnetism comes essentially from the Mn atom and to less extent to the interstitial region. However the contributions of Al, Ga, In and N atoms are quite insignificant. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]
[25] [26] [27] [28] [29] [30] [31]
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