Giant Spin Splitting in Optically Active ZnMnTe/ZnMgTe Core/ShellNanowiresPiotr Wojnar,*,† Elzbieta Janik,† Lech T. Baczewski,† Sławomir Kret,† Elzbieta Dynowska,†

Tomasz Wojciechowski,†,† Jan Suffczynski,‡ Joanna Papierska,‡ Piotr Kossacki,‡ Grzegorz Karczewski,†

Jacek Kossut,† and Tomasz Wojtowicz†

†Institute of Physics, Polish Academy of Sciences, Al Lotnikow 32/46, 02-668 Warsaw, Poland‡Institute of Experimental Physics, University of Warsaw, ul Hoza 69, 00-681 Warsaw, Poland

ABSTRACT: An enhancement of the Zeeman splitting as a result of theincorporation of paramagnetic Mn ions in ZnMnTe/ZnMgTe core/shell nanowiresis reported. The studied structures are grown by gold-catalyst assisted molecular beamepitaxy. The near band edge emission of these structures, conspicuously absent in thecase of uncoated ZnMnTe nanowires, is activated by the presence of ZnMgTe coating.Giant Zeeman splitting of this emission is studied in ensembles of nanowires withvarious average Mn concentrations of the order of a few percent, as well as inindividual nanowires. Thus, we show convincingly that a strong spin sp−d coupling isindeed present in these structures.

KEYWORDS: Nanowire, diluted magnetic semiconductors, spintronics, magneto-optical properties

Semiconductors doped with transition metal ions constitutea separate class of semiconductors called diluted magnetic

semiconductors (DMS), which continue to attract a greatattention because of possible applications in the field ofspintronics, that is, future electronics making use of the spindegree of freedom. Most interesting magnetic and magneto-optical properties of these materials arise from sp−d exchangeinteraction between the band carriers and magnetic ions.1,2 As aresult of this interaction an enhancement of spin-relatedproperties of carriers occurs; in particular, the giant Zeemansplitting of electronic levels is observed. In a parallel research,semiconductor nanowires have recently attracted a greatinterest due to emerging possible application as “buildingblocks” of future electronics,3−5 photonics,6,7 as well asnanosensors8,9 and photovoltaic nanodevices.10,11 Dopingnanowires with magnetic impurities would broaden theirpossible application range by including spintronic devices,12

such as spin filters or nanosensors of magnetic molecules.Moreover, the unique anisotropic properties of nanowires

may result in new and interesting magnetic properties of thesestructures and allow fundamental studies on the impact ofdimensionality and size on the magnetic properties of DMS's.In particular, the axial shape of DMS nanowires maysignificantly affect the magnetization energy inside nanowiresand result in a large magnetic anisotropy which may lead, inturn, to, for example, an easy magnetization axis along thegrowth direction of the nanowire.13 Second, the shape ofnanowire may also strongly affect the spin dynamics of carriersinside nanowire. In particular, the spin relaxation in such quasi-

one-dimensional structures could exhibit a considerable slowingdown or even the total suppression of it.14

Several reports concerning the introduction of magnetic ions(mostly Mn or Co) into nanowires have been recentlypublished involving various hosts coming from group II−VI,15−19 III−V,13,20,21 and IV22,23 families of semiconductors.Unfortunately, only a limited number of these reports addressthe sp−d exchange interaction in these structures. The presenceof sp−d exchange interaction was deduced in one report froman unusual positive magneto-resistance in magneto-transportmeasurements performed on individual ZnO:Co nanowire.24 Inanother attempt,16 the giant Zeeman splitting in ZnMnSenanowires was detected and studied by optical methods. Theemission under investigation was, however, dominated by theluminescence from particular type of structures called by theauthors “crooked nanowires”, that is, nanowire-like structureschanging their growth direction several times. Such structuresgrew simultaneously with the proper straight nanowires.Therefore, the direct observation of sp−d exchange interactionin nanowires still remains a challenge, as is the concept ofusefulness of ZnMnTe nanowires for spintronics.Here we present a method allowing us to overcome this

difficulty. In our previous report the growth of ZnMnTenanowires with high crystalline quality was presented.19 Thephotoluminescence (PL) spectrum of these particular struc-

Received: January 20, 2012Revised: June 21, 2012

Letter

pubs.acs.org/NanoLett

© XXXX American Chemical Society A dx.doi.org/10.1021/nl300254w | Nano Lett. XXXX, XXX, XXX−XXX

tures was, however, limited only to the internal Mn2+ transition,whereas the near band edge emission, which would enable thestudy of giant magneto-optical effects, was missing. In thepresent work, the near band edge emission from ZnMnTenanowires is activated by coating them with a ZnMgTe layer.We show that the near band edge emission exhibits a clear blueshift with an increasing Mn content inside ZnMnTe nanowirecores which confirms successful incorporation of the magneticions into their crystalline lattice of the core. Moreover, in anexternal magnetic field the excitonic emission exhibits a sizableredshift and strong circular polarization which are bothcharacteristic for the giant Zeeman splitting of the excitoniclevels and spin-polarization of the band carriers. Both effectsoriginate from the sp−d exchange interaction between thecharge carriers and magnetic Mn-dopants in our nanowires.ZnMnTe nanowires with various Mn contents controlled by

the temperature of the Mn effusion cell (TMn) are grown bymolecular beam epitaxy employing the vapor−liquid−solidgrowth mechanism induced by gold catalysts. In this Letter, wefocus on the properties nanowires grown with TMn = 810, 780,and 750 °C, which corresponds to a low Mn concentration ofthe order of only a few percent, as based on the referencegrowth of MBE layers. After the growth of 1.5 μm longZnMnTe nanowires at 430 °C on (111)B oriented GaAssubstrate, the growth temperature is considerably reduced tothe range of 250−300 °C for the deposition of the ZnMgTeshell. At such low temperatures the growth occurs mostly in theradial direction of the nanowires and results in an averageZnMgTe shell thickness of 30 nm after 7 min of deposition.The Mg content in the shell is about 20 at. %, as revealed by thepostgrowth X-ray diffraction and EDS measurements. The Mncontents inside ZnMnTe nanowires revealed by EDS measure-ments are, as expected, of the order of only few percent, 5.6%,3.5%, and 1% for TMn = 810 °C, 780 °C, and 750 °C,respectively. More accurate values will be determinedsubsequently by means of optical methods.Figure 1a shows a scanning electron microscope (SEM)

image of ZnMnTe/ZnMgTe core/shell nanowires grown atTMn = 810 °C. Nanowires grown at TMn = 780 and 750 °C arequalitatively very similar. Their diameters are typically in therange of 120−150 nm, whereas the presence of the shellcontributes significantly to these values. For comparison, typicaldiameters of ZnMnTe nanowires grown under nominallyidentical conditions without the outer coating are in the rangeof only 50−70 nm (Figure 1b). Therefore, we deduce theaverage thickness of a ZnMgTe shell of about 30 nm.Transmission microscope measurements performed with highresolution (HR TEM) confirms the crystalline character of thecore and shell semiconductors (with an exception of a thinamorphous oxide layer at the surface). In some nanowires theshell is monocrystalline and oriented as the core semi-conductor, as exemplified in Figure 1c, whereas in othernanowires the ZnMgTe coating includes other crystallinephases. Moreover, a few rotational twinnings which propagateperpendicularly to the growth axis in the cores of nanowires arealso detected. The impact of these particular defects on the PLfrom those nanowires remains, however, out of the scope of themanuscript, where we focus only on optically active nanowires,since we do not have means to perform both types ofmeasurements, HR TEM and magneto-PL, on the samenanowire.Most importantly, the presence of the ZnMgTe shell

activates the excitonic emission from ZnMnTe nanowires.

This is probably due to the surface passivation and,consequently, blocking the nonradiative recombination at thesurface. Figure 2a presents a typical PL spectrum of ZnMnTe/ZnMgTe core/shell nanowires (TMn = 750 °C) measured at alow temperature with the excitonic emission from ZnMnTe at2.32 eV. The broad emission band at 1.8 eV originates fromdeep level defects present in the crystalline structure ofZnMnTe nanowires and is also present in the PL spectrum ofuncoated ZnMnTe nanowires. Possible defects, which may beresponsible for this emission are zinc vacancies, as alreadyidentified for ZnSe nanowires.25 The emission related to theinternal Mn2+ transition, which is expected to appear at about2.0 eV, overlaps with the defect related emission and is notdistinguishable in the case of samples with relatively low Mncontent. However, in the case of the sample characterized byTMn = 810 °C (not shown) this emission manifests itself as anadditional kink at 2.0 eV on the defect-related emission band.In Figure 2b, the near band edge emission from three sampleswith various Mn contents and a reference sample withnonmagnetic ZnTe/ZnMgTe core/shell nanowires is shown.A clear blue shift of the emission with increasing Mn contentinside the nanowires is observed, which is mostly due to theincrease of the energy gap of ZnMnTe with the Mn content.This effect evidences directly the substitutional incorporation ofthe Mn ions into the crystalline structure of ZnMnTenanowires. A similar finding has already been reported forCdMnS nanowires.17 A rough estimate of the average Mnconcentration in our ZnMnTe nanowires can be made on thebasis of this energy shift. Assuming a linear dependence of theZnMnTe energy gap on the Mn content and the energy gapdifference between zinc blended ZnTe and MnTe equal to 0.75eV,26 the Mn content in those three samples is estimated to be

Figure 1. (a) Scanning electron microscope image of ZnMnTe/ZnMgTe core/shell nanowires, TMn = 810 °C, scale bar = 1 μm. (b)Comparison of a single ZnMnTe nanowire with ZnMgTe shell (left)and without the coating (right), scale bar = 200 nm. (c) Highcrystalline quality measured by HR TEM in the region of the ZnMgTecoating, scale bar 5 nm.

Nano Letters Letter

dx.doi.org/10.1021/nl300254w | Nano Lett. XXXX, XXX, XXX−XXXB

1.4%, 4.6%, and 8.1%. The emission energy may be, however,influenced also by strain present in radial nanowireheterostructures,27 as well as the diffusion of Mg ions fromthe shell into the cores of the nanowires. Therefore, a moreaccurate determination of the Mn content is attempted furtheron from magneto-optical measurements.To confirm that the emission under investigation originates,

indeed, from nanowires, almost all nanowires were removedfrom the substrate in an ultrasonic methanol bath. Indeed, theremaining crooked and defected structures on the surface donot reveal any luminescence in the near band edge energyregion of ZnTe as opposite to results reported in ref 16.The spectral width of the near band edge emission of

typically 20 meV was determined from the fits with Gaussianshape, and it does not vary significantly with the Mn content.Based on this result, we conclude that adding a small amount ofMn into ZnTe nanowires does not induce any significantincrease of the alloy disorder, whereas the contribution of themagnetization fluctuations, which is expected to be of the orderof only a few meV,28−30 is negligible compared to the width ofthe emission from the entire ensemble of nanowires.The nanowire PL was, next, measured in an external

magnetic field up to 7 T, as shown in Figure 3a. We observea considerable redshift of the emission energy of about 40 meVat 7 T for the sample with the highest Mn content. Moreover,this energy shift scales with the Mn concentration inside thenanowires, as clearly visible in Figure 3b, where the energyshifts for the three samples with various Mn contents areplotted. The higher the Mn concentration, the larger is theenergy shift. This finding points unambiguously that the sp−d

exchange interaction and the resulting giant Zeeman splittingare the origin of the observed energy shifts.This interpretation is further supported by a quantitative

analysis of the magnetic field dependence of the PL-spectralposition. It is remarkably well fitted, as shown in Figure 3b,with a modified Brillouin function which is well-known todescribe accurately the effects of sp−d exchange interaction inbulk DMS.31 The dependence is given by:

α β μΔ =

− ⎛⎝⎜

⎞⎠⎟E B T

N Nx S B

g B

kT( , )

( )2

0 0Mn 0 5/2

Mn B

eff (1)

where ΔE is the energy shift of the spectral position, B5/2 is theBrillouin function, and N0α = 0.19 eV and N0β = −1.1 eV arethe bulk ZnMnTe32 values for s−d and p−d exchange integrals,respectively. S0 is the bulk ZnMnTe32 effective spin of a Mnion, xMn is the molar fraction of Mn ions; gMn = 2 is the Landefactor for Mn ions, and Teff is the effective temperature of Mnspins, which includes the contribution from light induced spinheating effects and antiferromagnetic ion−ion exchangeinteraction.We assume in our considerations that mostly heavy hole

excitons are observable in the PL spectrum. The reason for thatis the strain originating from the presence of the ZnMgTecoating shell which splits the heavy and light holes similarly tothe case of a strained quantum well or quantum dot. There areonly two fitting parameters: xMn, the Mn content inside thenanowires, and the effective temperature of Mn sublattice Teff.From the best fits for the three samples under investigation,shown in Figure 3b, the average Mn concentration insidenanowires xMn is determined as 1.0%, 2.4%, and 3.5%, for thesamples characterized by TMn = 750 °C, TMn = 780 °C, and TMn

Figure 2. Photoluminescence spectra of ZnMnTe/ZnMgTe core/shell nanowires measured at 3.3 K, excited at 405 nm: (a) Typical spectrumconsists of the near band edge emission at about 2.32 eV and defect related emission at 1.8 eVsample with Mn content defined by TMn = 750 °C;(b) Focus on the near band energy emission region from samples with various Mn contents. A clear blue shift with increasing Mn content isobserved.

Nano Letters Letter

dx.doi.org/10.1021/nl300254w | Nano Lett. XXXX, XXX, XXX−XXXC

= 810 °C, respectively. Those values are slightly smaller thanestimated from the spectral position at 0 T. The difference maybe explained by the tensile strain originating from the ZnMgTeshell which is reduced with increasing Mn content in theZnMnTe cores and may result in an additional shift of thespectral position at 0 T. Some small deviations from assumedlinearity of the energy gap versus xMn may also lead to thisdiscrepancy. Parameters Teff amount to 6.1 K, 5.6 K, and 6.3 Kfor the samples characterized by TMn = 750 °C, TMn = 780 °C,and TMn = 810 °C, respectively. The absence of any trend inthese three values points out that heating effects have the majorcontribution to Teff. The contribution of antiferromagneticMn−Mn exchange interaction is expected to increase withincreasing Mn concentration, whereas its values may beestimated from the study of bulk ZnMnTe32 as 0.6 K, 1.0 K,and 1.7 K in the case of Mn content of 1.0%, 2.4%, and 3.5%,respectively.Circular polarization of the PL-emission further confirms that

the redshift reflects the giant Zeeman splitting of excitoniclevels. As shown in Figure 3c, the degree of circularpolarization, defined as [I(σ+) − I(σ−)]/[I(σ+) + I(σ−)],increases with the magnetic field and saturates at about 2 T,where I(σ+)(I(σ−)) is the intensity of the right-hand (left-hand) circularly polarized PL. This expected effect is a directconsequence of the spin polarization of carriers induced bydifferent populations of the levels split by the magnetic field. Indiluted magnetic semiconductors, where the Zeeman splitting is

enhanced by the presence of the magnetic dopants, nearly fullspin polarization of carriers is usually reached at relatively lowmagnetic fields at low temperature. In contrast to the emissionfrom bulk diluted magnetic semiconductors and dilutedmagnetic quantum dots, the emission from our dilutedmagnetic nanowires, however, remains not completelycircularly polarized (see inset in Figure 3a), and the maximumobserved degree of circular polarization is in the range of 30−50%, depending on the sample. This effect may be an inherentproperty of the nanowires whose emission is normally linearlypolarized due to a large contrast of dielectric constants of thenanowire and the surrounding space.33 This effect occursindependently of the applied magnetic field. Therefore, even incase of the total spin polarization of the band carriers at highmagnetic fields, which would result in 100% circular polar-ization in bulk DMS's, the dielectric environment of thenanowires induces the reduction of the degree of circularpolarization by admitting a component with opposite polar-ization.Moreover, a clear increase of the total emission intensity with

increasing magnetic field is observed (not shown), for example,by a factor of approximately three between 0 and 7 T for thesample characterized by TMn = 810 °C. We interpret this as aresult of the internal Mn2+ transition, which occurs at lowerenergies than the excitonic emission from ZnMnTe nanowires.In such conditions, an efficient excitation transfer from excitonsto Mn-ions occurs, which results in an effective decrease of theintensity of the near band edge emission.17,34,35 With anincreasing magnetic field, this excitation transfer is blocked dueto appearance of additional spin-dependent selection rules,which leads to an effective increase of the excitonic emissionintensity.17,34,35 This effect will be a subject of further studies.After decreasing the size of the excitation spot down to 2 μm,

we reduce the number of nanowires excited simultaneously tobe in the range 20−40 depending on the spatial position of theexcitation. As a result, the relatively broad emission band in thenear band edge energy region splits into several sharp lines withthe spectral width of about 2 meV at 0 T associated to theemission from individual nanowires. An example of suchindividual PL-line from the sample characterized by TMn = 810°C is shown in Figure 4a as a function of the magnetic field.The spectral position of those individual PL lines as a functionof the magnetic field can be well-fitted with a modified Brillouinfunction,31,32 from which the Mn content inside individualnanowires can be obtained (inset in Figure 4a). After a study ofabout 20 individual PL lines, we conclude that the Mn contentdoes not vary significantly from wire to wire, and its averagevalue is 3.5 ± 0.7%, which is consistent with the value obtainedfrom the energy shift of the ensemble emission. Moreover, thespectral width of those individual lines reflects directlymagnetization fluctuations28 inside a nanowire. After applyingthe external magnetic field, the spectral width clearly decreasesby a factor of 2, which is caused by damping of magnetizationfluctuations due to the magnetic field (Figure 4b).In conclusion, we have grown diluted magnetic ZnMnTe/

ZnMgTe core/shell nanowires by gold-catalyst assistedmolecular beam epitaxy process. The presence of the ZnMgTeshells activates the near band edge emission from ZnMnTenanowires and enables the study of giant magneto-opticaleffects in diluted magnetic nanowires. The incorporation of Mnions into the ZnTe nanowires is confirmed by the increase ofthe energy gap with increasing Mn content. Most importantly,however, after applying an external magnetic field, the giant

Figure 3. (a) PL dependence on the magnetic field up to 7 T for thesample with the highest Mn content corresponding to TMn = 810 °C,at T = 2 K excited at 450 nm. Inset: spectrum at 7 T in both circularpolarizations. (b) Spectral position versus magnetic field of the PL forsamples with various Mn contents, experimental data: open blackcircles, sample with Mn content defined by TMn = 810 °C; open bluetriangles, TMn = 780 °C; open red squares, TMn = 750 °C. Solid lines,fits with a modified Brillouin function (see text). (c) Degree of circularpolarization of the near band edge emission dependence on themagnetic field.

Nano Letters Letter

dx.doi.org/10.1021/nl300254w | Nano Lett. XXXX, XXX, XXX−XXXD

Zeeman splitting manifests itself as a considerable energy shiftof the excitonic emission which scales with the Mn contentinside the nanowires. This effect reflects directly the sp−dexchange coupling between carriers and magnetic Mn-ionsinside ZnMnTe nanowires. This finding is further confirmed bythe study of the circular polarization of the emission line whichreflects the spin polarization of the carriers inside nanowires.The degree of circular polarization clearly increases withincreasing magnetic field for all samples, and it saturates at 2 T.The degree of circular polarization, however, never reaches100%, which is caused probably by the magnetic fieldindependent linear polarization of the emission which is aninherent property of nanowire-related emission. A study ofindividual PL-lines in micro-PL-reveals that the Mn contentdoes not vary significantly from nanowire to nanowire pointinga homogeneous distribution of Mn in all nanowires in theentire sample. The most important aspect of this work is,however, that we clearly and directly proved that nanowireswith the key characteristics of diluted magnetic semiconductors,that is, with strong sp−d coupling determining new magneticproperties, can be grown.

■ AUTHOR INFORMATIONCorresponding Author*E-mail: wojnar@ifpan.edu.pl.NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSThe research has been supported by the European Unionwithin European Regional Development Fund throughInnovative Economy Grant (POIG.01.01.02-00-008/08), Na-tional Centre of Science (Poland) Grant DEC-2011/01/D/

ST5/05039, and Ministry of Higher Education (Poland) GrantIP 2011061171.

■ REFERENCES(1) Furdyna, J. K. J. Appl. Phys. 1988, 64, R29−R64.(2) Introduction to the Physics of Diluted Magnetic Semiconductors; Gaj,J. A., Kossut, J., Eds.; Series in Material Science, Vol. 144; Springer:New York, 2010.(3) Hayden, O.; Agarwal, R.; Lu, W. Nano Today 2010, 3, 12.(4) Lu, W.; Lieber, C. M. Nat. Mater. 2007, 6, 841.(5) Yan, H.; Choe, H. S.; Nam, S. W.; Hu, Y. J.; Das, S.; Klemic, J. F.;Ellenbogen, J. C.; Lieber, C. M. Nature 2011, 470, 240.(6) Huang, Y.; Duan, X. F.; Lieber, C. M. Small 2005, 1, 142.(7) Pauzauskie, P. J.; Yang, P. Mater. Today 2006, 9, 36.(8) Cui, Y.; Wei, Q.; Park, H.; Lieber, C. M. Science 2001, 293, 1289.(9) Patolsky, F.; Lieber, C. M. Mater. Today 2005, 8, 20.(10) Kelzenberg, M. D.; Turner-Evans, D. B.; Kayes, B. M.; Filler, M.A.; Putnam, M. C.; Lewis, N. S.; Atwater, H. A. Nano Lett. 2008, 8,710.(11) Tian, B.; Lieber, C. M. Abstr. Pap. Am. Chem. Soc. 2009, 238.(12) Kulkarni, J. S.; Kazakova, O.; Holmes, J. D. Appl. Phys. A: Mater.Sci. Process. 2006, A85, 277.(13) Stamplecoskie, K. G.; Ju, L.; Farvid, S. S.; Radovanovic, P. V.Nano Lett. 2008, 8, 2674.(14) Holleitner, A.; Sih, V.; Myers, R.; Gossard, A.; Awschalom, D.Phys. Rev. Lett. 2006, 97.(15) Chen, L.; Klar, P. J.; Heimbrodt, W.; Brieler, F. J.; Froba, M.;von Nidda, H. A.; Kurz, T.; Loidl, A. J. Appl. Phys. 2003, 93, 1326.(16) Cooley, B. J.; Clark, T. E.; Liu, B. Z.; Eichfeld, C. M.; Dickey, E.C.; Mohney, S. E.; Crooker, S. A.; Samarth, N. Nano Lett. 2009, 9,3142.(17) Na, C. W.; Han, D. S.; Kim, D. S.; Kang, Y. J.; Lee, J. Y.; Park, J.;Oh, D. K.; Kim, K. S.; Kim, D. J. Phys. Chem. B 2006, 110, 6699.(18) Radovanovic, P. V.; Barrelet, C. J.; Gradecak, S.; Qian, F.;Lieber, C. M. Nano Lett. 2005, 5, 1407.(19) Zaleszczyk, W.; Janik, E.; Presz, A.; Dluzewski, P.; Kret, S.;Szuszkiewicz, W.; Morhange, J. F.; Dynowska, E.; Kirmse, H.;Neumann, W.; Petroutchik, A.; Baczewski, L. T.; Karczewski, G.;Wojtowicz, T. Nano Lett. 2008, 8, 4061.(20) Sadowski, J.; Dluzewski, P.; Kret, S.; Janik, E.; Lusakowska, E.;Kanski, J.; Presz, A.; Terki, F.; Charar, S.; Tang, D. Nano Lett. 2007, 7,2724.(21) Urban, A.; Malindretos, J.; Seibt, M.; Rizzi, A. Nano Lett. 2011,11, 398.(22) Kazakova, O.; Kulkarni, J. S.; Holmes, J. D.; Demokritov, S. O.Phys. Rev. B 2005, 72.(23) Seong, H. K.; Kim, U.; Jeon, E. K.; Park, T. E.; Oh, H.; Lee, T.H.; Kim, J. J.; Choi, H. J.; Kim, J. Y. J. Phys. Chem. C 2009, 113, 10847.(24) Liang, W.; Yuhas, B. D.; Yang, P. Nano Lett. 2009, 9, 892.(25) Philipose, U.; Yang, S.; Xu, T.; Ruda, H. E. Appl. Phys. Lett.2007, 90, 063103.(26) Barilero, G.; Rigaux, C.; Menant, M.; Hau, N. H.; Giriat, W.Phys. Rev. B 1985, 32, 5144.(27) Skold, N.; Karlsson, L. S.; Larsson, M. W.; Pistol, M. E.; Selfert,W.; Tragardh, J.; Samuelson, L. Nano Lett. 2005, 5, 1943.(28) Maksimov, A. A.; Bacher, G.; McDonald, A.; Kulakovskii, V. D.;Forchel, A.; Becker, C. R.; Landwehr, G.; Molenkamp, L. W. Phys. Rev.B 2000, 62, R7767.(29) Wojnar, P.; Suffczynski, J.; Kowalik, K.; Golnik, A.; Karczewski,G.; Kossut, J. Phys. Rev. B 2007, 75, 155301.(30) Mackowski, S.; Jackson, H. E.; Smith, L. M.; Kossut, J.;Karczewski, G.; Heiss, W. Appl. Phys. Lett. 2003, 83, 3575.(31) Gaj, J. A.; Planel, R.; Fishman, G. Solid State Commun. 1979, 29,435.(32) Twardowski, A.; Swiderski, P.; Vonortenberg, M.; Pauthenet, R.Solid State Commun. 1984, 50, 509.(33) Wang, J.; Gudiksen, M. S.; Duan, X.; Cui, Y.; Lieber, C. M.Science 2001, 293, 1455.

Figure 4. (a) PL of an individual PL line in external magnetic fields upto 9 T, of the sample characterized by TMn = 810 °C; inset: spectralposition, and (b) spectral width of this PL line as a function of themagnetic field. The solid red line in the inset is the fit with a modifiedBrillouin function with fitting parameters xMn = 0.031 and Teff = 6.1 K.

Nano Letters Letter

dx.doi.org/10.1021/nl300254w | Nano Lett. XXXX, XXX, XXX−XXXE

(34) Kim, C. S.; Kim, M.; Lee, S.; Kossut, J.; Furdyna, J. K.;Dobrowolska, M. J. Cryst. Growth 2000, 214−215, 395−9.(35) Nawrocki, M.; Rubo, Y.; Lascaray, J. P.; Coquillat, D. Phys. Rev.B 1995, 52, R2241.

Nano Letters Letter

dx.doi.org/10.1021/nl300254w | Nano Lett. XXXX, XXX, XXX−XXXF