Origin and control of high-temperature ferromagnetism in semiconductors

Kuroda, Shinji; Nishizawa, Nozomi; Takita, K.; Mitome, Masanori; Bandô, Yoshio; Osuch, K.; Dietl, T.

doi:10.1038/nmat1910

Cited by 338 publications

(302 citation statements)

References 52 publications

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“…1,7,14 With an increased interest in the design of transparent electronics using p-type conductive oxides, it is found that by alloying Cu 2 O with other metal oxides such as SrO or Al 2 O 3 , the resultant material is both transparent and conducting, hence making its alloys potential candidates for developing transparent conducting electronic devices. 7 Concurrently, with the recent pursuit for spintronicsrelated technology, 15,16 magnetic oxide semiconductors are receiving much attention as potential candidate materials of interest and promoting the rather new and exciting field of "oxide spintronics." [17][18][19][20][21][22][23][24] Oxides, unlike the III-V compounds, tend to exhibit a much higher Curie temperature when doped and can accommodate a much higher doping concentration of magnetic impurity atoms.…”

Section: Introductionmentioning

confidence: 99%

Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties ofCu2−δO

et al. 2009

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Native defects in cuprous oxide Cu 2 O are investigated by using first-principles calculations based on density-functional theory. Considering the formation of copper and oxygen vacancies, antisites and interstitials, and a copper split-vacancy complex defect, we analyze the electronic structure and calculate their respective formation energies as a function of the change in Fermi level under both copper-rich and oxygen-rich conditions. We find that, under both growth conditions, the defect with the lowest formation energy is the simple copper vacancy, followed by the copper split-vacancy complex. Both low-energy copper defects produce hole states at the top of the valence band, largely accounting for the p-type conductivity in this material. In spite of the creation of dangling bonds at the nearest-neighbor O atoms, these copper defects are found to be spin neutral. Under oxygen-rich conditions, oxygen interstitials have low formation energies and are found to exhibit a ferromagnetic ordering with a total magnetic moment of 1.38 B and 1.36 B at the octahedral and tetrahedral sites, respectively. Considering the possibility of native defect formation at the surface of this material, we investigate the relative stability of both low-and high-index copper-oxide surfaces by comparing their surface free energies as a function of the change in oxygen chemical potential. Using the technique of ab initio atomistic thermodynamics, we then correlate the dependence of the calculated Gibbs free-surface energy as a function of oxygen pressure and temperature via the oxygen chemical potential. We identify two lowenergy surface structures, namely, Cu 2 O͑110͒ : CuO and Cu 2 O͑111͒-Cu CUS , with the former marginally more stable for oxygen-rich conditions and the latter more stable for oxygen-lean ͑or copper-rich͒ conditions. Cu 2 O͑110͒ : CuO is calculated to be nonmagnetic and Cu 2 O͑111͒-Cu CUS is calculated to be a ferromagnetic ordering, with a total magnetic moment of 0.91 B per defect. With the results for both bulk and surface native defects, we find that under oxygen-lean conditions, a ferromagnetic behavior could be attributed mainly to copper vacancy formation in the ͑111͒ surface of Cu 2 O while under oxygen-rich conditions, low-energy bulk oxygen interstitial defects induce a ferromagnetic character in the same material. This highlights the complementary role of bulk and surface native magnetic defects under different pressure and temperature conditions, especially at the nanoparticle scale where surface properties dominate.

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Section: Introductionmentioning

confidence: 99%

Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties ofCu2−δO

et al. 2009

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“…Most of the efforts concentrate on homogeneous doping of semiconductors with magnetic impurities [1,2,3,4], but the interfaces in complex oxides prove to be another source of novel behavior [5,6,7]. The unique magnetic properties of the hematiteilmenite system [8, 9, 10] (a canted antiferromagnet and a RT paramagnet, respectively) currently receive revived interest as a possible cause of magnetic anomalies in the Earth's deep crust and on other planets [11] as well as for future device applications [3,12,13].…”

mentioning

confidence: 99%

Interface magnetism inFe2O3/FeTiO3heterostructures

Pentcheva¹,

Nabi²

2008

Phys. Rev. B

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To resolve the microscopic origin of magnetism in the Fe2O3/FeTiO3-system, we have performed density functional theory calculations taking into account on-site Coulomb repulsion. By varying systematically the concentration, distribution and charge state of Ti in a hematite host, we compile a phase diagram of the stability with respect to the end members and find a clear preference to form layered arrangements as opposed to solid solutions. The charge mismatch at the interface is accommodated through Ti 4+ and a disproportionation in the Fe contact layer into Fe 2+ , Fe 3+ , leading to uncompensated moments in the contact layer and giving first theoretical evidence for the lamellar magnetism hypothesis. This interface magnetism is associated with impurity levels in the band gap showing halfmetallic behavior and making Fe2O3/FeTiO3 heterostructures prospective materials for spintronics applications.A challenge of today's materials science is to design ferromagnetic semiconductors operating at room-temperature (RT) for spintronics devices. Most of the efforts concentrate on homogeneous doping of semiconductors with magnetic impurities [1,2,3,4], but the interfaces in complex oxides prove to be another source of novel behavior [5,6,7]. The unique magnetic properties of the hematiteilmenite system [8, 9, 10] (a canted antiferromagnet and a RT paramagnet, respectively) currently receive revived interest as a possible cause of magnetic anomalies in the Earth's deep crust and on other planets [11] as well as for future device applications [3,12,13].Both hematite (a = 5.035Å, c = 13.751Å [14]) and ilmenite (a = 5.177Å, c = 14.265Å [15]) crystallize in a corundum(-derived) structure shown in Fig. 1 where the oxygen ions form a distorted hexagonal close packed lattice and the cations occupy 2/3 of the octahedral sites. In α-Fe 2 O 3 (space group R3c) there is a natural modulation of electronic density along the [0001]-direction where negatively charged 3O 2− layers alternate with positively charged 2Fe 3+ layers. At RT the magnetic moments of subsequent iron layers couple antiferromagnetically (AFM) in-plane with a small spin-canting, attributed to spin-orbit coupling [16,17,18]. In ilmenite, FeTiO 3 , Fe-and Ti-layers alternate, reducing the symmetry to R3 and the corresponding sequence is 3O 2− /2Fe 2+ /3O 2− /2Ti 4+ with AFM coupling between the Fe layers and T N =56-59 K [19].At the interfaces (IFs) in hematite-ilmenite exsolutions, charge neutrality is disrupted. One way to balance the excess charge at the interface is by a disproportionation in the Fe layer, now becom- * Electronic address: pentcheva@lrz.uni-muenchen.de ing mixed Fe 2+ and Fe 3+ . This lamellar magnetism hypothesis (LMH) was proposed by Robinson et al. [20] based on bond valence models and kinetic Monte Carlo simulations (kMC) with empirical chemical and magnetic interaction parameters. The increased technological interest in this system calls for an atomistic material specific understanding that can only be obtained from first principles calculatio...

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“…Figure 2 The low solubility of Cr in ZnTe, as in many of other DMSs, gives rise to an inhomogeneous Cr distribution as a result of the phase separation into regions containing low and high Cr contents [1]. The variation in the inhomogeneity with the flux ratio or the co-doping can be explained by the change in Cr charge state due to the shift of Fermi energy [5,6]. In the inhomogeneous Cr distribution, Cr-rich nano-scale regions, in which Cr spins order ferromagnetically, formed in the Cr-poor matrix give typical features of superparamagnetism; the magnetic anisotropy of the Cr-rich ferromagnetic clusters gives rise to the blocking phenomena as well as the appearance of ferromagnetic-like behaviors such as hysteretic magnetization curves.…”

Section: Resultsmentioning

confidence: 99%

“…x Cr x Te were correlated with the uniformity of Cr distribution in the crystal, which were systematically controlled by the flux ratio during the MBE growth or the co-doping of donor impurity iodine at a fixed average Cr content x ≅ 0.05 [5]. Here we report on the detailed analyses of the correlation between superparamagnetic behaviors and the uniformity of Cr distribution, including the data of a higher average Cr content of x ≅ 0.2.…”

Section: Introductionmentioning

confidence: 99%

Inhomogeneous Cr distribution and superparamagnetic behavior in magnetic semiconductor (Zn, Cr)Te

Ishikawa¹,

Nishizawa²,

Kuroda³

et al. 2010

AIP Conference Proceedings

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Abstract.The correlation between Cr spatial distribution and magnetic properties have been investigated for Zn1-xCrxTe films with low and high average Cr contents of x ≅ 0.05 and 0.2, which were grown by MBE under different Zn/Te flux or with the co-doping of donor impurity iodine. The EDS analysis reveals that the Cr distribution is strongly inhomogeneous in films grown under the Zn-rich condition or co-doped with iodine, in contrast to relatively homogeneous distribution in undoped films grown in the Te-rich condition. In the magnetization measurements, the superparamagnetic features, such as the blocking phenomena in the temperature dependence of magnetization, become more pronounced with the enhancement of inhomogeneity of Cr distribution.

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Origin and control of high-temperature ferromagnetism in semiconductors

Cited by 338 publications

References 52 publications

Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties ofCu2−δO

Native defect-induced multifarious magnetism in nonstoichiometric cuprous oxide: First-principles study of bulk and surface properties ofCu2−δO

Interface magnetism inFe2O3/FeTiO3heterostructures

Inhomogeneous Cr distribution and superparamagnetic behavior in magnetic semiconductor (Zn, Cr)Te

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