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Ferromagnetism in II–VI Diluted Magnetic Semiconductor Zn1−Xcrxte H

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Ferromagnetism in II–VI Diluted Magnetic Semiconductor Zn1−Xcrxte H Ferromagnetism in II–VI diluted magnetic semiconductor Zn1−xCrxTe H. Saito, W. Zaets, S. Yamagata, Y. Suzuki, and K. Ando Citation: J. Appl. Phys. 91, 8085 (2002); doi: 10.1063/1.1452649 View online: http://dx.doi.org/10.1063/1.1452649 View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v91/i10 Published by the American Institute of Physics. Related Articles Tunneling time and Hartman effect in a ferromagnetic graphene superlattice AIP Advances 2, 012123 (2012) Phase dependent room-temperature ferromagnetism of Fe-doped TiO2 nanorods AIP Advances 2, 012107 (2012) Engineering magnetic domains in manganite thin films by laser interference Appl. Phys. Lett. 100, 012403 (2012) Size effect on magnetic coupling in all-ferromagnetic superlattices Appl. Phys. Lett. 99, 263108 (2011) Weak d0 magnetism in C and N doped ZnO J. Appl. Phys. 110, 123917 (2011) Additional information on J. Appl. Phys. Journal Homepage: http://jap.aip.org/ Journal Information: http://jap.aip.org/about/about_the_journal Top downloads: http://jap.aip.org/features/most_downloaded Information for Authors: http://jap.aip.org/authors Downloaded 24 Jan 2012 to 150.29.211.127. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions JOURNAL OF APPLIED PHYSICS VOLUME 91, NUMBER 10 15 MAY 2002 Magnetic Semiconductors II Olle G. Heinonen, Chairman Ferromagnetism in II–VI diluted magnetic semiconductor Zn1ÀxCrxTe H. Saito,a),b) W. Zaets, S. Yamagata,c) Y. Suzuki,b) and K. Ando Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Tsukuba Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568, Japan Magnetic and transport properties of an epitaxial film of ferromagnetic II–VI diluted magnetic ͑ ͒ ϭ semiconductor DMS Zn1ϪxCrxTe ( x 0.035) were investigated. The Curie temperature TC of the film was about 15 K, which is the highest among the reported ferromagnetic II–IV DMS. Hall effect measurements at room temperature showed a hole concentration p of about 1ϫ1015 cmϪ3, which is several orders lower than that reported for carrier-induced ferromagnetic Zn1ϪxMnxTe. These results suggest that a ferromagnetic superexchange interaction between Cr ions is responsible for the observed ferromagnetism in Zn1ϪxCrxTe. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1452649͔ I. INTRODUCTION tron diffraction ͑RHEED͒ pattern was observed during the growth of the Zn Ϫ Cr Te films having a Cr concentration x Ferromagnetic diluted magnetic semiconductors ͑DMS͒ 1 x x up to 0.035. The Cr concentration x was calculated by elec- are important materials for use in spin electronics devices. tron probe micro-analysis ͑EPMA͒ and secondary ion mass Carrier-induced ferromagnetism has been reported in Mn- ͑ ͒ 1,2 spectroscopy SIMS . Magnetization measurements were doped DMS such as Ga1ϪxMnxAs, and p-doped 3 carried out using a superconducting quantum interference de- Zn Ϫ Mn Te. To achieve the ferromagnetism in Mn-doped 1 x x vice ͑SQUID͒ magnetometer under the magnetic field H ap- DMS, a large quantity of carriers ͑holes͒ is necessary to plied parallel to the film plane. The magnetization of the overcome an antiferromagnetic superexchange interaction Zn Ϫ Cr Te films was derived by subtracting the contribu- between Mn ions. However, it is difficult to control the con- 1 x x tion from the substrate, and the magnetization of the sub- ductive and magnetic properties independently in those ma- strate was also measured by a SQUID. The errors in the terials. Therefore, a ferromagnetic DMS with few carriers is magnetization of the Zn Ϫ Cr Te films are of the order of a desirable. Cr-doped II–VI DMS is expected to meet such a 1 x x few percent. Resistivity and Hall resistivity were measured demand, because a ferromagnetic superexchange interaction in the van der Pauw configuration. between Cr ions has been theoretically shown.4 Moreover, the band calculation results for Cr-doped II–VI DMS pre- dicted that the ferromagnetic state would be stable compared 5,6 to the nonmagnetic state. From the magneto-optical stud- III. RESULTS AND DISCUSSION ͑ ϭ ͒ ies, Zn1ϪxCrxM M S, Se, and Te were confirmed as being DMS,7–9 but no ferromagnetism has been reported.7–11 Figure 1 shows the magnetization curves for a ϭ Very recently, we successfully grew epitaxial films of Zn1ϪxCrxTe ( x 0.035) film at various temperatures T.A Zn1ϪxCrxTe having a relatively high Cr concentration x up to ferromagnetic hysteresis loop is clearly observed in the curve 0.035 and confirmed its ferromagnetism.12 In this study, we at Tϭ5 K. By magnetic circular dichroism ͑MCD͒ measure- report the detailed magnetic and transport properties of a ments, it was confirmed that the ferromagnetic hysteresis ϭ ferromagnetic Zn1ϪxCrxTe ( x 0.035) film. comes from Zn1ϪxCrxTe, and that the film is free from mag- netic precipitates.12 The hysteresis in the magnetization curve almost disappears at Tϭ10 K, as shown in the inset of II. EXPERIMENT Fig. 1, suggesting that the Curie temperature TC of the film is ϭ Epitaxial films of Zn1ϪxCrxTe having a zinc-blende type about 10 K. Above T 50 K, the curves show paramagnetic crystal structure were grown by a molecular beam epitaxy behavior. To determine TC , the Arrott-plots of the film with ͑MBE͒ method. A 100 nm thick ZnTe buffer layer was first xϭ0.035 at various T are given in Fig. 2. The plots show a ϭ grown on the GaAs substrate at TS 300 °C. Then a 200 nm linear relation in relatively high magnetic field ranges. The ϭ 2 ϭ thick Zn1ϪxCrxTe layer was grown at TS 250– 300 °C un- intercept of a linear extrapolation of M at H 0 gives a 2 der Te-rich conditions. A (2ϫ1) reflection high-energy elec- square of the spontaneous magnetization M S. With increas- 2 ϭ ing T, M S decreases and becomes zero at around T 15 K, ͒ which corresponds to T . It should be noted that the ob- a Electronic mail: [email protected] C ͒ b Also at CREST, Japan Science and Technology Corporation. tained TC of the film is about one order higher than that of c͒On leave from Toho University, Funabashi, Chiba, 274-0072, Japan. the reported carrier-induced ferromagnetic II–VI DMS. The 0021-8979/2002/91(10)/8085/3/$19.008085 © 2002 American Institute of Physics Downloaded 24 Jan 2012 to 150.29.211.127. Redistribution subject to AIP license or copyright; see http://jap.aip.org/about/rights_and_permissions 8086 J. Appl. Phys., Vol. 91, No. 10, 15 May 2002 Saito et al. FIG. 1. Magnetization curves for a Zn Ϫ Cr Te ( xϭ0.035) film at various 1 x x FIG. 3. Temperature dependence of susceptibility ͑᭹͒ and inverse suscep- temperatures. The inset shows a magnified view of the data at 5 and 10 K in tibility ͑᭺͒ foraZn Ϫ Cr Te ( xϭ0.035) film in a magnetic field of 10 kOe. low magnetic fields. 1 x x 13 ϭ ␳ TC ofaCd1ϪxMnxTe quantum well, p-doped 50 K.The value of is several orders higher than that of 3 2 Zn Ϫ Mn Te, and Be Ϫ Mn Te ͑Ref. 14͒ are 1.8, 2.4, and carrier-induced ferromagnetic DMS such as Ga1ϪxMnxAs, 1 x x 1 x x 3 2.5 K, respectively. and Zn1ϪxMnxTe. From the Hall effect measurement at Figure 3 shows the temperature dependence of suscepti- room temperature, p-type conduction is clearly observed as bility ␹ and the inverse susceptibility ␹Ϫ1 for the film with shown in the inset of Fig. 4. The carrier concentration p is ϫ 15 Ϫ3 xϭ0.035 in Hϭ10 kOe. It has been reported that the mag- estimated to be about 1 10 cm , which is 3–5 orders lower than that of the reported ferromagnetic DMS (p netic precipitate in Zn1ϪxCrxTe is a mainly NiAs-type CrTe Ϫ 10 ϭ1018–1020 cm 3). Therefore, an even higher T in compound whose TC is slightly above 300 K. No anomaly C ␹Ϫ Zn Ϫ Cr Te is expected by means of hole-doping. in the T curve is apparent in the vicinity of the TC of 1 x x CrTe, meaning that the film is free from the CrTe compound. In DMS, there are two possible magnetic interactions ͑ ͒ The ␹ϪT curve shows a large ␹, even at a much higher between localized spins. One is the carrier hole -induced temperature than the T estimated from the Arrott-plots, as interaction, and the other is the superexchange C 4,15,16 shown in Fig. 2. Fitting the ␹Ϫ1ϪT curve using the Curie– interaction. The former interaction is ferromagnetic, Weiss law, the paramagnetic Curie temperature obtained is whereas a sign of the latter interaction depends on the mag- 17,18 about 150 K, which is significantly higher than a ferromag- netic transition metals used. In the case of an Mn-doped DMS, the superexchange interaction between Mn ions is netic TC . These results indicate that the magnetic short- antiferromagnetic.15 It should be noted that the T of range order remains even far above TC . C The temperature dependence of resistivity ␳ for the film Zn1ϪxCrxTe is higher than that of the carrier-induced ferro- with xϭ0.035 is shown in Fig. 4. Down to Tϭ50 K, magnetic Zn1ϪxMnxTe, although the p of Zn1ϪxCrxTe is the curve shows semiconductive behavior. Resistivity be- several orders lower than that of Zn1ϪxMnxTe, as mentioned comes too high for a reliable measurement below about T FIG. 4. Temperature dependence of resistivity for a Zn1ϪxCrxTe ( x ϭ ϭ FIG. 2. The Arrott-plots of a Zn1ϪxCrxTe ( x 0.035) film at various tem- 0.035) film.
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