Article Single crystal growth and anisotropic magnetic properties of Li Sr[Li Fe N] 2 1−x x 2 PeterHöhn1,TanitaJ.Balle´2,ManuelFix2,YuriiProts1andAntonJesche2,* 1 Max-Planck-InstitutfürChemischePhysikfesterStoffe,NöthnitzerStr.40,D-01187Dresden,Germany 2 EPVI,CenterforElectronicCorrelationsandMagnetism,AugsburgUniversity,D-86159Augsburg, Germany 7 * Correspondence:[email protected];Tel.:+49-821-598-3659 1 0 VersionJanuary24,2017submittedtoInorganics;TypesetbyLATEXusingclassfilemdpi.cls 2 Abstract: Up to now, investigation of physical properties of ternary and higher nitridometalates n 1 a 2 was severely hampered by challenges concerning phase purity and crystal size. Employing a J modified lithium flux technique, we are now able to prepare sufficiently large single crystals of 3 3 2 4 thehighlyairandmoisturesensitivenitridoferrateLi2Sr[Li1−xFexN]2foranisotropicmagnetization 5 measurements. Themagneticpropertiesaremostremarkable: largeanisotropyandcoercivityfields ] of 7 Tesla at T = 2K indicate a significant orbital contribution to the magnetic moment of iron. i 6 c Altogether,thenovelgrowthmethodopensaroutetowardsinterestingphasesinthecomparatively s 7 - 8 recentresearchfieldofnitridometalatesandshouldbeapplicabletovariousothermaterials. l r t m Keywords: solution growth; magnetically hard materials; unquenched orbital moment; single 9 . 10 crystal;fluxgrowth t a m - d n 1. Introduction o c Binary transition metal nitrides attract considerable interest due to their valuable mechanical, [ electrical and magnetic properties. In contrast, chemistry and physics of multinary nitrides are 2 far less explored[1]. Nitridometalates of d metals T represent an interesting class of solid state v phases,whichcontainnitrogenasisolatedanionsN3−orfeaturecomplexanions[T N ]z−ofdifferent x y 7 dimensionalitieswithcoordinationnumbersofTbyNtypicallybetweentwoandfourandoxidation 2 1 states of the transition metals comparatively low. Whereas the bonding within these complex 5 anionsandframeworksisessentiallycovalent,nitridometalatesarestabilizedbypredominantlyionic 0 bondingthroughcounterionsofelectropositivemetalslikealkali(A)oralkaline-earth(AE)cations. . 1 Iron in nitridoferrates of alkali and alkaline-earth metals may be coordinated tetrahedrally 0 7 (Li3[FeIIIN4/2][2,3]) or trigonal-planar in isolated units ((Ca3N)2[FeIIIN3][4], Sr3[FeIIIN3][5], 1 Ba3[FeIIIN3][6], (Sr1−xBax)3[FeIIIN3][7], Sr8[FeIIIN3][FeIIN2][8,9]) as well as in oligomers : v (Ca [FeIIN ][10], Sr [FeIIN ][10]) and 1D chains (LiSr [FeIIN ][11], LiBa [FeIIN ][11]). Linear 2 2 2 2 2 2 3 2 2 3 Xi coordination is observed as linear dumbbells in Sr8[FeIIIN3][FeIIN2][8,9], Sr8[MnIIIN3][FeIIN2][12], r Sr2[FeIIN2][10], and Li4[FeIIN2][13], and in linear substituted chains [(Li1−xFeIx)N]2− in a Li2[(Li1−xFeIx)N][14–16],Li2Ca[(Li1−xFeIx)N]2[17],Li2Sr[(Li1−xFeIx)N]2[17],LiCa2[(FeI1−xLix)N2][18] and LiSr [(FeI Li )N ][19]. Structural data for the majority of nitridoferrates reported up to now 2 1−x x 2 werederivedfromsinglecrystaldata,whereasinmostcasessinglephasepowdersampleshadtobe employedfortheinvestigationofphysicalproperties,withtheexceptionofLi2[(Li1−xFeIx)N][20]and LiSr [(FeI Li )N ][19],wheresinglecrystalsofsufficientsizewereavailableforphysicalproperties 2 1−x x 2 investigations. The single crystal growth of nitrides is often challenging due to the large dissociation energy of the N molecule, the reactivity of the starting materials and enhanced vapor pressures. Only 2 SubmittedtoInorganics,pages1–10 www.mdpi.com/journal/inorganics VersionJanuary24,2017submittedtoInorganics 2of10 Sr Li N Li Fe 1-x x Figure1. CrystalstructureofLi2Sr[(Li1−xFex)N]2,theunitcellisindicatedbytheblacklines(space groupI4/amd).Feissubstitutedinlinear,two-foldcoordinationbetweenN. 1 recently, Li-rich flux was successfully used for the growth of large single crystals of LiCaN, Li N 3 and Li2(Li1−xTx)N with T = Mn,Fe,Co[20] and T = Ni[21]. Further development of the high temperaturecentrifugationaidedfiltrationtechnique[22–24]byadditionofNaandNaN toincrease 3 the basicity of the flux also enabled the growth of large single crystals of nitride metalides like Li Sr Ge N[25]. However,theextentofapplicationofthismethodtowardsmorecomplexsystems, 16 6 6 in particular transition metal rich ternary or quaternary nitridometalates that also contain alkaline earth elements, has not been investigated in detail. Magnetic properties were reported only for few nitridometalates containing alkaline-earth metals. Some of these phases show ferromagnetic (LiSr [CoN ][19]) or antiferromagnetic (LiSr [FeN ][19]) ordering. Furthermore, for many phases 2 2 2 2 (forexampleSr [MnN ] [MnN ][26])alargespin-orbitcouplingtogetherwithloworintermediate 8 3 2 2 spinstatesisbeingdiscussed. We shall present results on Fe-substituted Li SrN . The peculiar (almost) linear, two-fold 4 2 coordination of Fe makes this material particularly promising since unprecedented magnetic coercivity and anisotropy were found in Fe-substituted Li N, which shares the same structural 3 feature[16,27]. SynthesisandcrystalstructureofFe-substitutedLi SrN wasfirstreportedbyKlatyk 4 2 and Kniep[17]: Small single crystals sufficient for X-Ray diffraction were obtained by reaction of Li, Li (Li Fe )N and Sr N in a molar ratio of 7:6:4. The compound crystallizes in a tetragonal 2 0.66 0.33 2 lattice,spacegroup I4/amd(No. 141)witha =3.7909(2)Å,andc =27.719(3)Å.Asindicatedbythe 1 notationofthechemicalformula,Li2Sr[(Li1−xFex)N]2withx =0.46,thesubstitutedFeatomsoccupy only one of the two Li-sites (the one in two-fold coordination of N, see Fig.1). The Fe-coordination isnotstrictlylinear. RathertheN-Fe-Nangleamountsto177.4◦ asinferredfromthereportedcrystal structure[17]. The Fe-substitution causes a decrease of a but an increase of c by 0.8% and 2.5%, respectively, compared to the parent compound Li SrN [28]. No physical properties have been 4 2 reportedsofar. Here we show that Li2Sr[(Li1−xFex)N]2 single crystals of several millimeter along a side can be obtained from Li-rich flux. The large magnetic anisotropy and coercivity revealed a significant orbital contribution to the magnetic moment of Fe. Cu-substituted Li SrN was investigated as a 4 2 non-local-moment-bearingreferencecompound. 2. Results 2.1. Singlecrystalgrowth Due to the air and moisture sensitivity of both the reactants (Li, Sr N, NaN ) and the final 2 3 productLi2Sr[(Li1−xFex)N]2allmanipulationsincludinggrindingandweighing,aswellascomplete sample preparations for measurements were carried out in an inert gas glove box (Ar, O and H O 2 2 VersionJanuary24,2017submittedtoInorganics 3of10 Figure 2. Li2Sr[(Li1−xFex)N]2 single crystal (x = 0.41) on a millimeter grid and corresponding Laue-back-reflection pattern to the right showing the four-fold rotational symmetry along the crystallographicc-axis. ≤1ppm).Thetitlecompoundwasobtainedinformoflarge,blacksinglecrystalsfromthereactionof Sr N,Fe,LiandNaN inmolarratio1:1.8:36:1withNaN actingasnitrogensourceandLiacting 2 3 3 as flux and mineralizer. The mixtures with a total mass of roughly 0.6g were placed in a tantalum ampule[29]. Thewholedevicewassealedbyarcweldingunderinertatmosphereof700mbarargon andsubsequentlyencapsulatedinaquartztubewithaninternalargonpressureof300mbarinorder topreventoxidizationofthetantalum. ThesamplewasheatedfromroomtemperaturetoT =700◦C within 7h, annealed for 2h, then cooled to T = 300◦C within 400h, and finally centrifuged with 3000min−1toseparatethesinglecrystalsofablackishcolorfromtheexcessflux.Besidesseverallarge singlecrystalsofthetitlephase,smallamountsofsinglecrystallineLi3NandLiSr2[(Fe1−xLix)N2][19] werealsoobtained. Usingatwo-probemultimeter,thedifferentphasesshowedremarkablydifferent resisitivitiesenablingthediscriminationofthevariousphases. A representative Li2Sr[(Li1−xFex)N]2 single crystal is shown in Fig.2. The samples show a plate-like habit with the crystallographic c-axis oriented perpendicular to the large surface as confirmedbyLaue-back-reflection(rightpanelinFig.2).Thespot-sizeoftheX-Raybeamwassimilar tothesamplesize. An Fe-concentration of x = 0.42 was determined by energy-dispersive X-Ray analysis (EDX) based on the Fe:Sr ratio and assuming fully occupied Sr-sites. An almost identical value of x = 0.41 was found by chemical analysis by means of inductively coupled plasma optical emission spectroscopy (ICP-OES; accessible is the Li:Sr:Fe ratio) and was confirmed with a second sample takenfromthesamebatch. TheobservedslightLi-excessof0.15performulaunit(0.19fortheother sample),isattributedtosmallamountsofLi-richfluxremnants. 2.2. Crystalstructure Figure3showstheX-RaypowderdiffractionpatternmeasuredongroundLi2Sr[(Li1−xFex)N]2 single crystals. No foreign phases were detected. The region between 2θ = 20◦-25◦ was excluded due to amorphous constituents that are created by degradation during the measurement. Lattice parametersofa =3.79536(9)Åandc =27.6492(13)ÅandanFeoccupancyofx =0.32wereobtained by Rietveld refinement. The decrease in a and increase in c in comparison to the parent compound Li SrN (a = 3.822(2)Åandc = 27.042(9)Å[28])areslightlysmallerthanreportedinRef.[17](x = 4 2 0.46,a =3.7909(2)Åandc =27.719(3)Å)inaccordancewithasomewhatlowerFeconcentration. Smaller crystals were obtained from crushed samples and selected for single crystal X-Ray diffraction. TheresultsaresummarizedinTable1. PowderaswellassinglecrystalX-Raydiffraction revealed an Fe-concentration of x = 0.32. This is somewhat smaller than the values obtained by EDX and chemical analysis and indicates that the Fe concentration may vary between different VersionJanuary24,2017submittedtoInorganics 4of10 Figure3.X-RaydiffractionpatternmeasuredongroundsinglecrystalsofLi2Sr[(Li1−xFex)N]2(CoKα radiation,λ=1.78892Å).TickmarkscorrespondtoreflectionpositionsofLi2Sr[(Li1−xFex)N]2. Table1.SinglecrystalstructurerefinementforLi2Sr[(Li1−xFex)N]2. crystalsystem tetragonal spacegroup I4/amd(No.141) 1 a(Å) 3.8011(1) c(Å) 27.586(3) Feoccupancy 0.32(1) cellvolume(Å3) 398.57(5) Z 4 ρ (gcm−3) 2.907 calcd crystalcolor,habit black,tetragonalcolumn crystalsize(mm) 0.02x0.02x0.07 µ(Mo ,mm−1) 15.52 Kα 2θrange(◦) 5.90-59.60 diffractometer RIGAKU wavelength(Å) 0.71069(MoKα) monochromator graphite temperature 293K scanmode profiledatafromφscans measuredreflections 3355 independentreflections 187 observedreflections[Fo>4σ(Fo)] 2919 R 0.041 int structuresolutionmethod direct numberofparameters 17 goodness-of-fitonF2 1.081 wR2 0.078 R1[Fo>4σ(Fo)] 0.030 R1(alldata) 0.035 residualelectrondensity(e×10−6pm−3) 1.24/-1.70 VersionJanuary24,2017submittedtoInorganics 5of10 ( a ) ( b ) L i S r [L i F e N ] 2 .0 2 0 .5 9 0 .4 1 2 1 2 µ H = 7 T 0 1 0 1 .5 H ^ c -3) -1l)Fe H II c 8 lmFe o1 .0 o m 6 m 3 6 0 -6 10m0 .5 4 -1(cid:1) (1 (cid:1) ( 2 0 .0 µ = 5 .4 (cid:1) /F e c eff B 1 0 0 · L i S r [L i C u N ] 2 0 .6 0 .4 2 0 0 1 0 0 2 0 0 3 0 0 0 1 0 0 2 0 0 3 0 0 T ( K ) T ( K ) Figure4. Magneticsusceptibilityχ= M/HpermolFeasafunctionoftemperatureforfieldapplied parallel and perpendicular to the crystallographic c-axis. (a) A pronounced anisotropy with larger χ for H ⊥ c (open, red symbols) is observed up to room temperature. The molar susceptibility of Li Sr[(Li Cu )N] multipliedbyafactorof100isshownforcomparison(blue,dottedline,H⊥c). 2 0.6 0.4 2 (b)ThetemperaturedependenceoftheinversesusceptibilityroughlyfollowsaCurie-Weisslawfor T>150K. samples; the slight difference between powder and single crystal data may also stem from slight inhomogeneities within the samples. The single crystal used for the magnetization measurements (seebelow)wasdirectlyanalyzedbyICP-OESandshowedanironconcentrationofx =0.41. 2.3. Magneticproperties The temperature-dependent magnetic susceptibility χ(T) = M/H measured parallel and perpendicular to the crystallographic c-axis is shown in Figure 4a (field-cooled in µ H = 7T). A 0 temperature-independentcontributionofaferromagneticimpurityphase(withaCurietemperature significantly above room temperature, presumably elemental Fe or Fe O ) was subtracted by 3 4 assuming that the intrinsic, local-moment contribution of the title compound is linear in field at T = 300K (analogous to the Honda-Owen method). A pronounced anisotropy is observed over thewholetemperaturerangeinvestigated. Theratioofχ⊥c/χ(cid:107)c increasesuponcoolingfromavalue of2atT =300Kto12atT =2K. In order to confirm the proposed, unusual valence state of Fe(I)[17], we performed further magnetizationmeasurementsonLi Sr[(Li Cu )N] (thesamplewasgrownsimilartotheisotypic 2 0.6 0.4 2 title compound Li2Sr[(Li1−xFex)N]2). The local moment behavior associated with the spin-1/2 of Cu(II) is supposed to be markedly different from the one of Cu(I). As shown by the blue, dotted line in Fig.4a, the susceptibility of Li Sr[(Li Cu )N] does not show local moment behavior and 2 0.6 0.4 2 is indeed negligibly small compared to the one of the Fe-substituted homologue. The largely temperature independent value of χ = −5(1)·10−10m3mol−1 is in reasonable agreement with the ionic diamagnetic contribution of the Li SrN host material of χ = −6·10−10m3mol−1 {assuming 4 2 χ(Li1+) = −0.2·10−10m3mol−1[30], χ(Sr2+) = −2·10−10m3mol−1[31] and χ(N3−) = −1.6· 10−10m3mol−1[32]}. Accordingly, the observed non-local moment behavior ofLi2Sr[(Li1−xCux)N]2 impliesthepresenceofCu(I)andsupportsavalencestateofFe(I). The inverse susceptibility roughly follows a Curie-Weiss law for T = 150K-300K (Figure4b). For H ⊥ c an effective moment of µ = 5.4µ per Fe and a ferromagnetic Weiss temperature of eff B Θ = 49Kwereobtained. Thefittothedataconsideredaminordiamagneticcontributionofχ = W 0 −1.5·10−8m3mol−1 (10% of the absolute value at room temperature). The slope of χ−1 suggests a VersionJanuary24,2017submittedtoInorganics 6of10 L i S r [ L i F e N ] ( a ) ( b ) 2 0 .5 9 0 .4 1 2 2 T = 1 0 K T = 2 ...2 0 K 2 ^ H c H II c 1 1 ) ) e e F F /0 0 / B B (cid:1) (cid:1) ( ( M ^ M H c - 1 - 1 T ( K ) 2 , 4 , 6 , 8 , - 2 1 0 , 1 4 , 2 0 - 2 - 8 - 6 - 4 - 2 0 2 4 6 - 6 - 4 - 2 0 2 4 6 8 (cid:1) H ( T ) (cid:1) H ( T ) 0 0 Figure5. Isothermalmagnetizationinµ perFeat T = 10K.(a)Largehysteresisemergesforfield B appliedperpendiculartothec-axis(whichisperpendiculartotheN-Fe-N’molecularaxis’). (b)The hysteresis for H ⊥ c increases rapidly with decreasing temperature. Spontaneous magnetization disappearsfortemperatureslargerthanT∼16K. similarvalueoftheeffectivemomentforH (cid:107) c,however,thesmallabsolutevalueofχincombination withalargeantiferromagneticWeisstemperatureprohibitsanaccurateestimate. Theisothermalmagnetizationinµ perFeasafunctionofanappliedmagneticfieldatT =10K B isshowninFigure5a. For H (cid:107) cthemagnetizationincreasesslowlywiththeappliedfieldinalinear fashionwithoutanyappreciablehysteresis. Themagnetizationissignificantlylargerfor H ⊥ c and exceedsvaluesof2µ perFe. However,nosaturationisobservedevenatthelargestavailablefield B ofµ H = 7T.Inaccordancewiththelargeanisotropy,apronouncedhysteresisloopwithacoercive 0 fieldofµ H =1.2TformsforH ⊥ c. Thecoercivityfieldincreasesrapidlyuponcooling(Fig.5b). At 0 c thelowestaccessibletemperature T = 2Kthecoercivityreachesalmost7T.Thehysteresisvanishes fortemperatureshigherthanT ≈ 16K.Furthermore,the M−H loopsareasymmetricforT < 14K: The(fieldcooled)valueinµ H = +7Tislargerthanthecorrespondingvaluefoundatµ H = −7T. 0 0 Thesmallanomaliesat H ∼ 0andat M ∼ 1µ resultfromthesubtractionoftheferromagnetic B impurity contribution (which is not fully temperature independent) and a zero-crossing of the raw datasignal,respectively. Asignificantin-planeanisotropyfordifferentorientationsperpendicularto thec-axiscouldbepresent,inparticular[100]vs. [110](seediscussion). Thecloserinvestigationof thisanisotropy,however,isbeyondthescopeofthispublication. 3. Discussion The successful use of a Li-rich flux for the growth of large single crystals of Fe-substituted Li SrN has been anticipated since there are only a few binaries known that may compete with the 4 2 formation of this compound. Among those, Li-Sr binaries are not considered exceedingly stable as indicated by their low peritectic decomposition temperatures (< 200◦C)[33]. Nevertheless, a good solubilityofSrinLiisinferred.OnlyafewSr-Nbinarycompoundsareknownandnonofthoseseem tobestableinthepresenceofLi. NobinarycompoundsofSr-FeorSr-Ta(whichmaypreventtheuse ofTacrucibles)areknown. Furthermore, ourworkshowsthatLi Nisnotsostablethatitprevents 3 the formation of other nitrides. Whether the related compounds LiSr Fe N [11] or LiSr FeN [19] 2 2 3 2 2 (isotypic to LiSr CoN [34]) can be grown as large single crystals by adjusting temperature profile 2 2 and/orratioofthestartingmaterialsissubjectofongoingresearch.Thesituationissimilarforternary VersionJanuary24,2017submittedtoInorganics 7of10 andmultinarynitridesthatcontainotheralkalineearthand/orothertransitionmetalsanditseems notunlikelytofindawiderangeofapplicationsfortheLi-fluxmethod. ThemagneticpropertiesofLi2Sr[(Li1−xFex)N]2,inparticularthelargeanisotropyandcoercivity, aremostremarkably. Thereareonlyafewmaterialsknownthatshowcoercivityfieldsintherange ofµ H ∼7Torabove. Thosearemelt-spunribbonsofrare-earth-basedDy-Fe-BandTb-Fe-Balloys 0 c (reported are µ H = 6.4T for both materials[35] and µ H = 7.7T for the latter one[36]). For 0 c 0 c transition-metal-basedcompounds,theonlyexamplesweareawareofareLuFe O (µ H =9T[37] 2 4 0 c and µ H = 11T[38]) and Fe-substituted Li N (µ H = 11.6T[27]). The large magnetic anisotropy 0 c 3 0 c andcoercivityofbothmaterialsiscausedbyasignificantorbitalcontributiontothemagneticmoment ofFe(see[39]fortheformerand[21,40–42]forthelatterone). Whereastheemergenceoftheorbital momentinLuFe O isaresultofacomplexinterplaybetweenchargeordering, ferroelectricityand 2 4 ferrimagnetism[43], the orbital moment in Fe-substituted Li N seems to be directly linked to the 3 linear, two-fold coordination of Fe[27]. Such a linear molecule or linear chain is not subject to a Jahn-Teller distortion[44,45] which is the driving force for the quenching of the orbital magnetic momentthatisusuallyobservedintransitionmetals. As found for Fe-substituted Li3N, the magnetic hard axis of Li2Sr[(Li1−xFex)N]2 is oriented perpendiculartotheN-Fe-N’molecularaxis’(seeFigures1and 5). Accordingly, thereisnounique easy-axis present in Li2Sr[(Li1−xFex)N]2 since the N-Fe-N molecules run along both the a- and the b-axes(incontrasttoFe-substitutedLi NwheretheN-Fe-Nmoleculesdodefinetheeasyaxisandare 3 orientedalongtheunique,hexagonalc-axis).Themagnetizationinthea-bplaneisthereforeexpected √ to reach between 1/2 and 1/ 2 of the saturation magnetization of Fe corresponding to field along (cid:104)100(cid:105) and (cid:104)110(cid:105), respectively. The increase of the magnetization for H ⊥ c is only slightly larger than for H (cid:107) c (see Fig.5a). This implies similar large magnetic anisotropy energies for (cid:104)110(cid:105) and (cid:104)001(cid:105)(withrespectto(cid:104)100(cid:105)). To summarize, the large magnetic anisotropy and coercivity observed in Li2Sr[(Li1−xFex)N]2 give strong evidence for a significant orbital contribution to the magnetic moment of Fe. The similarities to Li2(Li1−xFex)N[21,27] are apparent. The origin of this behavior is attributed to the (almost)linear,two-foldcoordinationFe. Ourworkshowsthatsmalldeviationsfromlinearity,that is a N-Fe-N angle of ∼177◦ instead of 180◦, do not prevent the formation of unquenched orbital moments. Thisfindingsignificantlyincreasesthenumberofpotentialcandidatesforrare-earth-free hard-magneticmaterials. 4. MaterialsandMethods Starting materials were lithium rod (Evochem, 99%), iron powder (Alfa Aesar, 99.998%), strontium nitride (Sr N) powder [prepared from strontium metal (Alfa Aesar, distilled dentritic 2 pieces, 99.8%) and nitrogen (Praxair, 99.999%, additionally purified by molecular sieves)], and sodium azide (NaN ) powder (Roth, 99%) as a further nitrogen source. Tantalum ampules were 3 producedon-sitefrompre-cleanedtantalumtubeandtantalumsheetinanarcfurnacelocatedwithin aglovebox. LaboratorypowderX-raydiffractiondataoffinelyground(gray)powdersampleswerecollected on a Huber G670 imaging plate Guinier camera using a curved germanium (111) monochromator and Cu-Kα1 radiation in the range 4◦ ≤ 2θ ≤ 100◦ with an increment of 0.005◦ at 293(1)K. The powder samples were placed between Kapton foils to avoid degradation in air. Preliminary data processingwasdoneusingtheWinXPowprogrampackage[46]. Rietveldrefinementofthestructure of Li2Sr[(Li1−xFex)N]2 was performed with the software package Jana2006[47]. Small intervals of the diffraction pattern between 2θ = 20◦-25◦ corresponding to amorphous degradation products were excluded during the refinement. After background correction, profile and lattice parameters wererefinedbyusingPseudo-VoigtprofilefunctionsandBerar-Baldinozzi’sasymmetrymodelbefore refiningatomicpositionsandisotropicthermaldisplacementfactors. VersionJanuary24,2017submittedtoInorganics 8of10 The crystal structure and the composition of the title compound Li2Sr[(Li1−xFex)N]2 was refined from single-crystal X-ray diffraction data which were collected at room temperature on a Rigaku AFC7 four circle diffractometer equipped with a Mercury-CCD detector (Mo-Kα radiation, graphite monochromator). After data collection the structures were solved by direct methods, using SHELXS-97[48] and subsequently refined by using the full-matrix least-squares procedure with SHELXL-97[49]. Further details on the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (Fax: +49-7247-808-666; e-mail: crysdata@fiz-karlsruhe.de), on quoting the depository number CSD-xxx, thenamesoftheauthors,andthejournalcitation. ThemorphologyoftheLi2Sr[(Li1−xFex)N]2sampleanditsmetalcompositionwereinvestigated using a scanning electron microscope Philips XL30 equipped with a Bruker Quantax EDX-System (Silicondriftdetector, LaB cathode). TheEDXdatawereprocessedusingtheEsprit-Software. The 6 composition of the samples was further analyzed by inductively coupled plasma optical emission spectroscopy(ICP-OES)usingaVarianVista-MPX.Tothisextentthesamplesweredissolvedindilute hydrochloric acid solution (4ml of 37% hydrochloric acid added to 46ml deionized water). Laue back reflection pattern were taken with a digital Dual FDI NTX camera manufactured by Photonic Science(tungstenanode,U =20kV).Themagnetizationwasmeasuredusinga7TMagneticProperty MeasurementSystem(MPMS3)manufacturedbyQuantumDesign. Acknowledgments: The authors thank Dr. U. Burkhardt, P. Scheppan, and S. Hückmann for experimental assistance.A.Mohs,A.HerrnbergerandK.Wiedenmannareackowlegdedfortechnicalsupport.Thisworkwas supportedbytheDeutscheForschungsgemeinschaft(DFG,GermanResearchFoundation)-GrantNo.JE748/1. AuthorContributions: P.H.grewthesinglecrystalsandanalyzedpowderandsinglecrystalX-Raydiffraction datathatwerecollectedbyY.P.T.B.performedthemagnetizationmeasurementsandinterpretedthedata. M.F. collectedandanalyzedLaue-back-reflectiondata.A.J.wrotethepaperwiththehelpofallauthors. ConflictsofInterest:Theauthorsdeclarenoconflictofinterest. Bibliography 1. Kniep,R.; Höhn,P. 2.06-Low-ValencyNitridometalates. InComprehensiveInorganicChemistry{II},2nd ed.;Reedijk,J.;Poeppelmeier,K.,Eds.;Elsevier:Amsterdam,2013;pp.137–160. 2. Gudat,A.;Kniep,R.;Rabenau,A.;Bronger,W.;Ruschewitz,U.Li3FeN2,aternarynitridewith∞1[FeN34/−2] chains:Crystalstructureandmagneticproperties. J.Less-CommonMet.1990,161,31–36. 3. Nishijima, M.; Takeda, Y.; Imanishi, N.; Yamamoto, O.; Takano, M. 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