International Journal of Hydrogen Energy 26 (2001) 503–505 www.elsevier.com/locate/ijhydene The eect of hydrogen incorporation in the nanocrystalline iron particles on their magnetic properties A.A.Novakova a ; * ,T.Yu.Kiseleva a ,O.V.Agladze a ,N.S.Perov a ,B.P.Tarasov b a Department of Physics, Moscow M.V.Lomonosov State University, 117234 Moscow, Russia b Institute for New Chemical Problems RAS, 142432, Chernogolovka, Russia Abstract TheeectofhydrogenonthestructureandmagneticpropertiesofnanocrystallineironpowderswasinvestigatedbyXRD, M ossbauer spectroscopy and magnetic measurements. The nanocrystalline Fe powders were produced by two methods: iron hydroxidereductioninhothydrogenowandhigh-energyballmillingofcarboxylicironinhydrogenatmosphereduring8h. Theformationofnanocrystallinestatewithmeangrainsize13nmwasobtainedinbothcases.Hydrogenincorporationinthe grain boundaries was observed in the nanocrystalline ball-milled iron. Formation of oxy-hydroxide amorphous surface layer was observed in “reduced” sample ? 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. 1. Introduction Nanocrystalline(n.c.)materialsareknownaspolycrystals withthesizeofindividualcrystallitesintheorderofseveral (1–10) nm. They consist of the following two components [1–3]: a crystalline component formed by all atoms located in the lattice of the crystallites (grains) and an interfacial component comprising all atoms which are situated in the grain boundaries between the crystallites. The structure of grain boundaries depends on how the n.c. material was prepared and strongly aects its magnetic properties [4,5]. Inthisworkwehavestudiedtheinuenceofgrainbound- arystructureonmagneticpropertiesoftwon.c.ironsamples, having the same grain size, but dierent boundary struc- ture.BothsampleswereproducedinactiveH2 gas-working atmosphere. 2. Experimental Samples of n.c. iron were produced with the same (∼13 nm) mean grain size by two methods: from iron ∗ Corresponding author. E-mail address: aan@runar.phys.msu.su (A.A. Novakova). hydroxidereductioninhothydrogenow(at600 ◦ C)andby high-energy ball milling of carboxylic iron in hydrogen at- mosphereduring8h.Thelatticeparameters,grainsizeand strainswereanalyzedbyXRD.Diractionpatternswasob- tained with the use of Rigaku D-MAX Cu K .M ossbauer spectra were obtained at RT and 78 K in transmission ge- ometry with 50 mCi Co 57 (Rh) source. Magnetic measure- mentsofcoerciveforceandmagnetizationwerecarriedout byvibratingsampleanisometerinmagnetometermode.De- termination of absorbed hydrogen was made by thermo- gravimetryindryheliumatmospherein“Netzsch”STA-409 thermoanalyser. 3. Results The results of a detail analysis on magnetization curves forn.c.Fesampleswiththesamegrainsize13nmarepre- sented in Table 1. There is a drastic dierence between the magnetic parameters of the samples: ball-milled Fe show increased coercive force Hc . At the same time, reduced Fe shows valuable saturation magnetization  decrease. To study the reasons of such behavior we performed structural andM ossbauer measurements. Fig. 1(a) reects XRD patterns of the samples with car- boxylicFeasreference.TheresultsofX-raydiractionline prole analysis with evaluated average lattice parameter a, grain size D and lattice strain  are presented in Table 1. 0360-3199/01/$20.00 ? 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved. PII:S0360-3199(00)00083-5