Magnetic properties of nanoscale crystalline maghemite obtained by a new synthetic route

AbstractIn this work we describe the synthesis and characterization of maghemite nanoparticles obtained by a new synthetic route. The material was synthesized using triethylamine as a coprecipitation agent in the presence of the organic ligand N,N′-bis(3,5-di-tert-butyl-catechol)-2,4-diaminotoluene (LCH3). Mössbauer spectrum at 4K shows typical hyperfine parameters of maghemite and Transmission Electron Microscopy images reveal that the nanoparticles have a mean diameter of 3.9nm and a narrow size distribution. AC magnetic susceptibility in zero field presents an Arrhenius behavior with unreasonable relaxation parameters due to the strong influence of dipolar interaction. In contrast when the measurements are performed in a 1kOe field, the effect of dipolar interactions becomes negligible and the obtained parameters are in good agreement with the static magnetic properties. The dynamic energy barrier obtained from the AC susceptibility results is larger than the expected from the average size observed by HRTEM results, evidencing the strong influence of the surface contribution to the anisotropy

Magnetism of atomically thin fcc Fe overlayers on an expanded fcc lattice: Cu84Al16(100)

We present experimental data on the magnetic properties of atomically thin fcc (γ-phase) Fe films (1-6 atomic layer nominal thickness) epitaxially grown on (Formula presented) obtained by linear magnetic dichroism in the angular distribution of Fe (Formula presented) core photoelectrons excited by linearly polarized synchrotron radiation. The sign and magnitude of the Fe (Formula presented) photoemission magnetic asymmetry indicates the onset of in-plane ferromagnetism at 2.5(2) monolayer (ML) thickness of γ-Fe. The Curie temperature is 288(2) K for 4 ML thickness. The magnetic splitting of the Fe (Formula presented) core hole sublevels is 1.10(2) eV, i.e., the same value as measured for a bcc-Fe(100) surface where large surface and near-surface enhanced moments contribute. These results characterize the epitaxial γ-Fe on (Formula presented) as a high-spin ferromagnet for thickness up to 4 ML, with an average magnetic moment per iron atom of 2.5(1)(Formula presented) A phase transition occurs between 4 and 5 ML thickness: the magnetic order of the pseudomorphic γ-Fe film decreases consistently with the breaking into two phases with the deeper layers in a low-spin and/or antiferromagnetic phase and surface restricted ferromagnetism, similar to the case of γ-Fe/Cu(100). © 1998 The American Physical Society

Synthesis Of Granular Fe-al2o3 By The Sol-gel Method

We have investigated the structural and magnetic properties of a granular composite of iron particles dispersed in alumina matrix, obtained starting from an aqueous solution containing Al(NO3)3·9H2O and FeSO4·7H2O. The samples were characterized by X-ray diffraction and fluorescence, Mössbauer spectroscopy (MS) and vibrating sample magnetometry (VSM). Samples with 7.8 wt% Fe were submitted to two different heat treatments with the aim of reducing the iron oxides into metallic iron. Series A was submitted to calcination between 100°C and 1200°C, followed by reduction in ultra pure H2 at 600°C during 2 h; Series B was submitted to reduction at 600°C or at 1000°C directly after drying at 80°C. As determined by MS, we have obtained a maximum of 24% metallic Fe in series A and of 74% α-Fe in series B, after reduction at 1000°C. By VSM, at 300 K, the maximum coercivity of 819 Oe was obtained for the samples calcinated at 800°C before reduction and an almost constant saturation magnetization of 2 emu/g. In series B, samples with 74% α-Fe presented a coercivity of 370 Oe and a saturation magnetization of 9.0 emu/g. The applied synthesis method seems to be an interesting alternative way to obtain magnetic Fe nanoparticles in a non-magnetic alumina matrix. © 1998 Elsevier Science B.V. All rights reserved.177-181PART 1247248Haneda, K., (1987) Can. J. Phys., 65, p. 1233Dormann, J.L., (1993) Mat. Sci. Eng. A Struc. Mater., 168, p. 217Chien, C.L., (1995) Ann. Rev. Mat. Sci., 25, p. 129Xiao, G., Chien, C.L., (1987) Appl. Phys. Lett., 51, p. 1280Shull, R.D., (1990) J. Appl. Phys., 67, p. 4490Suwa, Y., Roy, R., Komarneni, S., (1986) Mat. Sci. Eng., 83, p. 151Hargrove, R.S., Kündig, W., (1970) Solid State Commun., 8, p. 303Shull, R.D., Kerch, H.M., Ritter, J.J., (1994) J. Appl. Phys., 75, p. 684

Magnetism Of Epitaxial Fexni1-x Films On Cu90au10(1 0 0)

We have investigated the effect of an expansion of the lattice parameter on the magnetic properties of fcc FeNi films. Epitaxial FexNi1-x ultrathin films (0.58< x<0.92) were grown on a Cu90Au10(1 0 0) single crystal, a substrate with lattice parameter 1.4% larger than the pure copper. The magnetism of the FeNi films was explored by using linear magnetic dichroism in the angular distribution of the photoelectrons (LMDAD). The LMDAD measurements were carried out at 160 K, using synchrotron radiation with an energy of 140 eV. Although we have observed a gradual decrease of the Fe 3p LMDAD asymmetry in the 67-80 at% Fe concentration range, as already reported for FexNi1-x on Cu(1 0 0), for the Fe-rich region (x>∼0.80) we have obtained a Fe 3p asymmetry of 6%, suggesting that the lattice expansion of the FeNi due to the epitaxy on Cu90Au10(1 0 0) stabilizes the high-spin ferromagnetic state up to higher Fe concentration values. © 2006 Elsevier B.V. All rights reserved.3102 SUPPL. PART 322742276Wassermann, E.F., (1990) Ferromagn Mater., 5. , Buschow K.H.J., and Wohlfarth E.P. (Eds), North-Holland, AmsterdamSchumann, F.O., Willis, R.F., Goodman, K.G., Tobin, J.G., (1997) Phys. Rev. Lett., 79, p. 5166Abrikosov, I.A., Erikson, O., Soderling, P., Skriver, H.L., Johansson, B., (1995) Phys. Rev. B, 51, p. 1058Entel, P., Hoffmann, E., Mohn, P., Schwarz, K., Moruzzi, V.L., (1993) Phys. Rev. B, 47, p. 8706van Schilfgaarde, M., Abrikosov, I.A., Johansson, B., (1999) Nature, 400, p. 46Ruban, A.V., (2005) Phys. Rev. B, 71, p. 054402Abrikosov, I.A., (2006) J. Magn. Magn. Mater., 300, p. 211Crisan, V., Entel, P., Ebert, H., Akai, H., Johnson, D.D., Staunton, J.B., (2002) Phys. Rev. B, 66, p. 014416Foy, E., (2003) Phys. Rev. B, 68, p. 094414Liberati, M., Panaccione, G., Sirotti, F., Prieto, P., Rossi, G., (1999) Phys. Rev. B, 59, p. 4201. , and references thereinJanke-Gilman, N., Hochstrasser, M., Willis, R.F., (2004) Phys. Rev. B, 70, p. 18443

Four-fold magnetic anisotropy in a Co film on MgO(001)

AbstractThe development of devices based on magnetic tunnel junctions has raised new interests on the structural and magnetic properties of the interface Co/MgO. In this context, we have grown ultrathin Co films (≤30Å) by molecular-beam epitaxy on MgO(001) substrates kept at different temperatures (TS). Their structural and magnetic properties were correlated and discussed in the context of distinct magnetic anisotropies for Co phases reported in the literature. The sample characterization has been done by reflection high energy electron diffraction, magneto-optical Kerr effect and ferromagnetic resonance. The main focus of the work is on a sample deposited at TS=25°C, as its particular way of growth has enabled a bct Co structure to settle on the substrate, where it is not normally obtained without specific seed layers. This sample presented the best crystallinity, softer magnetic properties and a four-fold in-plane magnetic anisotropy with Co〈110〉 easy directions. Concerning the samples prepared at TS=200 and 500°C, they show fcc and polycrystalline structures, respectively and more intricate magnetic anisotropy patterns

The Effect Of Atmosphere Composition In Plasma Nitrogenation Of Sm 2fe17

The change on the structural and magnetic properties of the Sm 2Fe17 compound as the ratio of H2/N2 forming the mixture of the atmosphere in a plasma chamber used to nitride this compound varied, was investigated by Mössbauer spectroscopy and X-ray diffraction. Our results show that the increase of the hydrogen concentration in the mixed H2/ N2 atmosphere reduces the formation of the nitrogen-rich phases, Sm2Fe17N8 and Sm 2Fe17N11and increases the formation of the Sm2Fe17N3 phase, whose maximum values are obtained for 70% H2 in the gas mixture. © 2003 Elsevier B.V. All rights reserved.272-276SUPPL. 1e1859e1861Coey, J.M.D., Sun, H., (1990) J. Magn. Magn. Mater., 87, pp. L251Otani, Y., Hurley, D.P.F., Sun, H., Coey, J.M.D., (1991) J. Phys.: Condens. Matter., 69, p. 5584Skomski, R., Brennan, S., Qi, Q.N., Coey, J.M.D., (1995) J. Magn. Magn. Mater., 158, p. 299Colucci, C.C., Gama, S., Labaki, L.C., Ribeiro, C.A., (1993) J. Magn. Magn. Mater., 125 (1-2), p. 161Kurney, A.S.W., Moran, R.M., Nitriding of steels - On review (1986) The Heat Treating Source Book, p. 127. , P.S. Gupton (Ed.), Metals Park, ASMIriyama, T., Kobayashi, K., Imaoka, N., Fukuda, T., Kato, H., Nakawa, Y., (1992) IEEE Trans. Magn., 28, p. 2326Ardisson, J.D., Macedo, W.A.A., Araújo, R.C., Gama, S., (2000) J. Appl. Phys., 87, p. 532

Magnetic linear dichroism in photoemission from Fe on Cu84Al16(100) and Cu3Au(100)

We have investigated the magnetic properties of monolayers of FCC Fe grown epitaxialy on Cu84Al16(1 0 0) and on ordered Cu3Au(1 0 0), substrates that present lattice parameters 1% and 3.7% bigger than pure Cu. The magnetic measurements were carried out by linear magnetic dichroism in the angular distribution of photoelectrons (LMDAD), using linearly polarized synchrotron radiation. The LMDAD measurements of the Fe 3p core levels show that starting from 2.5 monolayers (ML) for Fe/Cu84Al16(1 0 0) and from 4 ML for Fe/Cu3Au(1 0 0) these FCC Fe films present in-plane ferromagnetism. The 9% increase of the magnetic splitting of the Fe 3p LMDAD peak-to-peak asymmetry measured for Fe/Cu3Au(1 0 0) suggests an increase of the Fe magnetic moment with increasing volume of the high-spin FCC Fe films

High Coercivity In A New Molecular Iron-based Magnet

A new molecule-based magnet containing Fe(II), Fe(III) and Cu(opba)2- (opba = ortho-phenylenebis(oxamato)) was synthesized. The samples were characterized by infrared spectroscopy, elemental analysis, atomic absorption, macroscopic magnetometry, X-ray diffraction, and 57Fe Mössbauer spectroscopy. Magnetic measurements show that the compound presents a transition temperature below 15 K and a high coercivity, around 6.3 kOe at 4.2 K. At room temperature, the Mössbauer spectrum is dominated by a broad doublet characteristic of Fe(II), and a small fraction of Fe(III) ions is also identified. At 4.2 K, the spectrum shows clear magnetic splitting. © 2001 Elsevier Science Ltd.20Nov/1414311434Vaz, M.G.F., Pinheiro, L.M.M., Stumpf, H.O., Alcântara, A.F.C., Golhen, S., Ouahab, L., Cador, O., Kahn, O., (1999) Chem. Eur. J., 5, p. 1486Surville-Barland, C., Ruiz, R., Aukauloo, A., Journaux, Y., Castro, I., Cervera, B., Julve, M., Sapinã, F., (1998) Inorg. Chim. Acta, 278, p. 159Kahn, O., (1993) Molecular Magnetism, , Verlag-Chemie, New YorkTamaki, H., Zhong, Z.J., Matsumoto, N., Kida, S., Korkawa, M., Achiwa, N., Hashumoto, Y., Okawa, H., (1992) J. Am. Chem. Soc., 114, p. 6974Stumpf, H.O., Pei, Y., Kahn, O., Sletten, J., Renard, J.P., (1993) J. Am. Chem. Soc., 115, p. 6738Ruiz, R., Surville-Barland, C., Journaux, Y., Colin, J.C., Castro, I., Cervera, B., Julve, M., Sapinã, F., (1997) Chem. Mater., 9, p. 201Stumpf, H., Pei, Y., Ouahab, L., Berre, F.L., Codjovi, E., Kahn, O., (1993) Inorg Chem., 32, p. 5687Vaz, M.G.F., Stumpf, H., Ardisson, J.D., Macedo, W.A.A., (2001) J. Magn. Magn. Mater., , in pres

Structural And Magnetic Properties Of Nife2o 4-sno2 Nanocomposite

The structural and magnetic properties of the NiFe2O 4-SnO2 composite, obtained by ball-milling during different times, were investigated by X-ray diffraction, small-angle X-ray scattering, Mössbauer spectroscopy and vibrating sample magnetometry. The results showed the reduction of the crystalline particle size and modification in the nature of the system interfaces as a consequence of the mechanical treatment. Specimens with smaller particles displayed strong superparamagnetism. Large variation of the hysteresis loops for the different milling times was observed. © 2003 Elsevier B.V. All rights reserved.272-276III22112213Chien, C.L., (1995) Ann. Rev. Mater. Sci., 25, p. 129Mandai, K., (2002) J. Appl. Phys., 92, p. 501Zhou, Z.H., (2002) J. Appl. Phys., 91, p. 6015Verdes, C.G., (2001) J. Appl. Phys., 89, p. 7475Albuquerque, A.S., (1999) J. Magn. Magn. Mater., 192, p. 277Albuquerque, A.S., (2001) J. Magn. Magn. Mater., 226, p. 1379Kellerman, G., (1997) J. Appl. Crystallogr., 30, p. 880Vong, C.G., (1973) J. Appl. Cryst., 6, p. 81Bale, H., Schmidt, P.W., (1983) Phys. Rev. Lett., 53, p. 59