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15 Aug 2009

Volume 106, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 106, 041101 (2009); http://dx.doi.org/10.1063/1.3207769 (21 pages)

Robert C. Runkle, L. Eric Smith, and Anthony J. Peurrung
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Fitting transmission and Faraday rotation spectra of [Bi3Fe5O12/Sm3Ga5O12]m magneto-optical photonic crystals

D. O. Dzibrou and A. M. Grishin

J. Appl. Phys. 106, 043901 (2009); http://dx.doi.org/10.1063/1.3195067 (6 pages) | Cited 4 times

Online Publication Date: 17 August 2009

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A consistent microscopic approach is developed to simulate the transmittance and Faraday rotation in all-garnet heteroepitaxial magneto-optical photonic crystals (MOPCs). To compare the experimental and simulation results, [Bi3Fe5O12/Sm3Ga5O12]m (BIG/SGG) MOPC designed to operate at a telecommunication wavelength λres = 980 nm was chosen. It was composed of [BIG/SGG]5 and [SGG/BIG]5 distributed Bragg reflectors with a microcavity layer of BIG in between. The dispersion relations of the diagonal and off-diagonal elements of the permittivity tensor math for BIG in the electric dipole approximation were obtained from the simulation of the transmittance and Faraday rotation for a reference single layer BIG film. Revealed dispersion relations were then combined with the 4×4 matrix formalism for magnetic superlattices to compute transmission and Faraday rotation spectra of the MOPC. The results of numerical simulations were found to be in good agreement with the experimental ones.
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78.20.Ls Magneto-optical effects
42.70.Qs Photonic bandgap materials

Effects of oxygen depletion on photoinduced and transport properties of thin films of charge-ordered manganites

V. N. Smolyaninova, G. Yong, Rajeswari M. Kolagani, K. Karki, and B. Hofmann

J. Appl. Phys. 106, 043902 (2009); http://dx.doi.org/10.1063/1.3195059 (5 pages) | Cited 2 times

Online Publication Date: 19 August 2009

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In this paper, we report a study of conductive and photoinduced properties of charge-ordered Bi0.4Ca0.6MnO3 thin films with different oxygen contents. The oxygen content of the films was varied following different annealing or deposition protocols. Change in film’s resistivity during annealing reflects oxygen dynamics at high temperatures. It was found that oxygen-deficient films exhibit a significant increase in the photoinduced resistivity changes and the lifetime of photoinduced conductive phase. Possible origin of this effect is discussed.
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73.61.Ng Insulators
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Strong asymmetry of microwave absorption by bilayer conducting ferromagnetic films in the microstrip-line based broadband ferromagnetic resonance

M. Kostylev

J. Appl. Phys. 106, 043903 (2009); http://dx.doi.org/10.1063/1.3187547 (14 pages) | Cited 10 times

Online Publication Date: 19 August 2009

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Peculiarities of broadband ferromagnetic resonance response of conducting magnetic bilayer films have been studied theoretically. The film thickness was assumed to be smaller than the microwave magnetic skin depth. Excitation of magnetization precession by a homogeneous microwave field incident from one surface of the film has been considered, which mimics the microwave field of a wide microstrip transducer. Strong asymmetry of the response has been found. Depending on the order of layers with respect to the transducer location either the first higher-order standing spin-wave mode or the fundamental mode shows the largest response. This effect is explained as shielding of the transducer field by eddy currents in the films. This shielding remains very efficient for films with thicknesses below the microwave magnetic skin depth. This effect may be useful for studying buried magnetic interfaces and should be accounted for in future development of broadband inductive ferromagnetic resonance methods.
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78.70.Gq Microwave and radio-frequency interactions
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.30.+q High-frequency effects; plasma effects
73.50.Mx High-frequency effects; plasma effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance

Anderson localization enhanced ferromagnetism in Zn0.95Co0.05O

Michael Snure and Ashutosh Tiwari

J. Appl. Phys. 106, 043904 (2009); http://dx.doi.org/10.1063/1.3197138 (7 pages) | Cited 4 times

Online Publication Date: 21 August 2009

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We report an enhancement in the ferromagnetic characteristics of Zn0.95Co0.05O thin films due to the localization of charge carriers. Epitaxial thin films of Zn0.95−xCo0.05GaxO (x = 0–0.05) were grown on single-crystal sapphire (0001) substrates by pulsed laser deposition technique. The role of charge carrier localization on the electrical and magnetic properties of ZnO:Co was studied by introducing Ga into the system. It was observed that Ga plays a significant role in affecting both the electrical transport mechanism as well as the magnetization of the material. Electrical resistivity of Zn0.95Co0.05O at room temperature was ∼ 96 mΩ cm and exhibited metal-like temperature dependence, although strongly influenced by electron-electron (e-e) interactions. Strong e-e interaction was understood to arise because of the randomness introduced in the crystal potential of ZnO by the cobalt dopants. As the Ga dopants are introduced, randomness in crystal potential and hence the disorder further increases resulting in the Anderson localization of the carriers. The increase in localization was accompanied by a significant enhancement in the magnetic moment from 0.75μB/Co in Zn0.95Co0.05O films to 1.6μB/Co in Zn0.90Co0.05Ga0.05O.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Fg Pulsed laser ablation deposition
73.61.Ga II-VI semiconductors
75.50.Pp Magnetic semiconductors

Flux-closure chirality control and domain wall trapping in asymmetric magnetic ring

X. H. Wang, W. K. Peng, and W. S. Lew

J. Appl. Phys. 106, 043905 (2009); http://dx.doi.org/10.1063/1.3197413 (4 pages) | Cited 5 times

Online Publication Date: 21 August 2009

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A technique for flux-closure chirality control and domain wall trapping at the narrowest position in asymmetric magnetic ring is proposed. Micromagnetic simulation work was performed on permalloy asymmetric magnetic rings to observe its magnetic switching behavior. By controlling the lateral geometric features, the ring asymmetry, and the thickness of the film, a local vortex-free reversal process and well-controlled chirality of flux closure can be achieved. Furthermore, a domain wall trapping feature is also observed at the narrow arm of the asymmetric ring, which corresponds to the phenomenon that the magnetic domain wall does not annihilate until the magnetization in the wide arm reversed in a relatively large magnetic field. A phase diagram of the asymmetric ring switching behavior shows that the switching regimes (e.g., the domain wall propagation or nucleation annihilation) of the asymmetric rings and the domain wall pinning depend mainly on the film thickness.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Coherent suppression of picosecond magnetization precession in the presence of spin waves in a Ni81Fe19 microstripe

Anjan Barman, H. Sakata, T. Kimura, Y. Otani, and Y. Fukuma

J. Appl. Phys. 106, 043906 (2009); http://dx.doi.org/10.1063/1.3200963 (5 pages) | Cited 1 time

Online Publication Date: 21 August 2009

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We present the experimental and micromagnetic simulation studies of coherent suppression of picosecond magnetization precession in Ni81Fe19 (Permalloy) microstripes with widths of 5, 10, and 12 μm and length of 100 μm in the presence of multiple spin wave modes. The lateral confinement of the microstripes causes spin wave modes of frequencies adjacent to each other, and the local suppression of the modes was experimentally achieved with field pulses of slightly different durations but with same rise time and fall time. Micromagnetic simulations show that application of the pulse field causes a large angle ( ∼ 135°) reorientation of the magnetization, followed by a precession. At a particular value of pulse duration (suppression time), the magnetization returns back to the equilibrium position and suddenly becomes parallel to the effective field so that the torque on the magnetization vanishes. However, this applies to localized regions due to the presence of spin wave modes of slightly different frequencies along the short axis of the microstripe. Pulses of little under- or overwidth cause the precession to continue at a slightly different frequency, suggesting that the spin wave modes are not truly localized but there are overlapping regions where one mode dominates but the other modes appear more prominently when the dominating mode is suppressed. For stripes of different widths, similar spatial dependence of suppression time was observed. However, the average value of the suppression time decreases with reduced width of the stripe as a result of the increase in precession frequency.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Ds Spin waves

Influence of annealing atmosphere on the magnetic properties of SiO2/Fe/SiO2 sandwiched nanocomposite films

P. L. Zhu, F. Xue, Z. Liu, Y. L. Fan, Z. M. Jiang, and X. J. Yang

J. Appl. Phys. 106, 043907 (2009); http://dx.doi.org/10.1063/1.3204474 (6 pages) | Cited 2 times

Online Publication Date: 21 August 2009

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The magnetic properties of SiO2/Fe/SiO2 nanocomposite films are studied by magnetic force microscopy and vibrating sample magnetometer. The films were fabricated by alternately depositing SiO2, Fe, and SiO2 on Si substrates with magnetron sputtering followed by thermal annealing. It is found that the annealing atmosphere significantly influences the sample structure, composition, and magnetic properties. The samples annealed in forming gas show much better magnetic properties than those annealed in vacuum and in N2. The saturation magnetization can reach 200 emu/g, fairly close to the value of bulk Fe, and the coercivity can reach 400 Oe, much higher than 10 Oe of the bulk Fe. X-ray photoelectron spectroscopic depth profile measurement was carried out to study the mechanism of the strong influence of annealing atmosphere. For the samples annealed in forming gas, Fe nanoparticles are mildly oxidized, forming thin shells of Fe2O3 surrounding them, which is beneficial for maintaining the ferromagnetic behavior and enhancing the coercivity of nanoparticles.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.16.-c Methods of micro- and nanofabrication and processing
75.50.Dd Nonmetallic ferromagnetic materials
79.60.Jv Interfaces; heterostructures; nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Magnetic separation and inelastic tunneling in self-doped manganite films

V. Markovich, G. Jung, S. I. Khartsev, M. I. Tsindlekht, A. M. Grishin, Ya. Yuzhelevski, and G. Gorodetsky

J. Appl. Phys. 106, 043908 (2009); http://dx.doi.org/10.1063/1.3197855 (8 pages) | Cited 1 time

Online Publication Date: 25 August 2009

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Magnetic and transport properties of 100 nm thick La0.9MnO3−δ self-doped manganite films have been investigated in the temperature range 5–300 K. The films exhibit a paramagnetic to ferromagnetic transition at TC = 194 K. The temperature dependence of the resistivity shows a metal-insulator transition at 204 K and a strong resistivity increase below 160 K. The magnetoresistance was always negative and slightly bias dependent. Variations in resistivity with magnetic field and current are nonhysteretic, while the temperature dependence of the resistivity exhibits unusual inverse thermal hysteresis. The magnetic field independent inverse thermal hysteresis is strongly influenced by a thermal history of the sample. The data suggest that nonlinear low temperature transport is dominated by inelastic tunneling through intrinsic tunnel junctions formed by phase-separated ferromagnetic metallic domains and insulating antiferromagnetic matrix.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.47.Lx Magnetic oxides
75.50.Ee Antiferromagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.30.+h Metal-insulator transitions and other electronic transitions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.20.My Galvanomagnetic and other magnetotransport effects
73.61.Ng Insulators

Tunable ferromagnetism by oxygen vacancies in Fe-doped In2O3 magnetic semiconductor

P. F. Xing, Y. X. Chen, Shi-Shen Yan, G. L. Liu, L. M. Mei, and Z. Zhang

J. Appl. Phys. 106, 043909 (2009); http://dx.doi.org/10.1063/1.3202287 (4 pages) | Cited 5 times

Online Publication Date: 25 August 2009

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Fe-doped In2O3 films with well defined bcc (440) texture were grown on r-cut sapphire at different oxygen pressures by pulsed laser deposition. Nonmonotonic dependence of ferromagnetism on oxygen pressure has been observed. Under optimal deposition conditions, the saturation magnetization can reach 2.5μB/Fe atom. Moreover, the ferromagnetism can be reversed between the higher magnetization state and the lower magnetization state by alternate annealing in vacuum and in air. All these features are well explained by a modified model of F-center mediated ferromagnetism.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.ag Semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Fg Pulsed laser ablation deposition
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.jd Vacancies
81.05.Hd Other semiconductors
81.40.Gh Other heat and thermomechanical treatments

Investigation of self- and in-field dependent n-value of Tb-doped (Bi,Pb)-2212 superconductor

P. M. Sarun, S. Vinu, R. Shabna, and U. Syamaprasad

J. Appl. Phys. 106, 043910 (2009); http://dx.doi.org/10.1063/1.3204665 (4 pages)

Online Publication Date: 25 August 2009

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Knowledge of the electric field versus current density (E-J) characteristics is very important for the development of superconducting high-field magnets particularly for operation in the persistent mode. A systematic study of the E-J characteristics and the associated n-indices has been carried out both in self and applied fields in respect of Tb-doped (Bi,Pb)-2212, a promising superconductor for high-field application. The results on n-indices and pinning energy (Uc) show that the flux-lines in (Bi,Pb)-2212 doped with an optimum concentration of Tb (x = 0.075–0.100) are in glass-state and hence the material allows maximum current to flow with minimum dissipation of energy. Further, it has been shown that the modified material is a promising candidate for persistent mode superconducting magnets.
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74.72.-h Cuprate superconductors
61.72.up Other materials
84.71.Ba Superconducting magnets; magnetic levitation devices
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.25.F- Transport properties

High order finite element model for core loss assessment in a hysteresis magnetic lamination

Yu Zhang, Ming-C. Cheng, Pragasen Pillay, and Brian Helenbrook

J. Appl. Phys. 106, 043911 (2009); http://dx.doi.org/10.1063/1.3176492 (7 pages) | Cited 1 time

Online Publication Date: 26 August 2009

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A dynamic model for evaluating core losses in a hysteretic magnetic lamination is developed and then solved using a high-order finite element method that includes time-history effects. It is demonstrated that the dynamic hysteresis effect, previously used to explain the frequency dependence of B−H loops, is not a fundamental phenomenon of magnetic materials but originates from the skin effect. It arises because the measured flux density is an averaged value over the lamination thickness, and this value is influenced strongly by the skin effect. The study verifies that, unlike the observed dynamic hysteresis effect, the local B−H loop is in fact frequency independent. The developed dynamic core loss model is thus derived based on the frequency-independent B−H loop. It is shown that the developed model can accurately evaluate the losses for different frequencies and thicknesses based on only one set of inputs of an experimental B−H loop at one low frequency without a huge database of experimental losses.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
72.30.+q High-frequency effects; plasma effects
75.40.Mg Numerical simulation studies

Induced ferromagnetism in Mn3N2 phase embedded in Mn/Si3N4 multilayers

E. Céspedes, E. Román, Y. Huttel, J. Chaboy, J. García-López, A. de Andrés, and C. Prieto

J. Appl. Phys. 106, 043912 (2009); http://dx.doi.org/10.1063/1.3203997 (10 pages) | Cited 4 times

Online Publication Date: 26 August 2009

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Room temperature ferromagnetism has been obtained for different sets of Mn/Si3N4 multilayers prepared by sputtering. In order to find the most suitable conditions to stabilize the ferromagnetic ordering in this system, the evolution of the magnetic properties has been studied for films in which the Si3N4 layer thickness was maintained constant while that of the Mn layer was varied, [Mn(tm)/Si3N4(3.4 nm)]n, and conversely, in [Mn(0.7 nm)/Si3N4(tsn)]43 samples, in which the Mn layer thickness was kept constant while varying the Si3N4 layer thickness. Structural, compositional, electronic and magnetic characterizations have been performed by means of x-ray reflectometry, Rutherford backscattering spectrometry, x-ray photoemission spectroscopy, x-ray absorption, and superconducting quantum interference device for further knowledge of the magnetic-structural relationship in this system. Our results show that the peculiar magnetic behavior of these films is mainly related to the stabilization of a slightly distorted Mn3N2 phase that is induced by the Si3N4 at the interfaces. For samples with larger Mn layer thickness, metallic Mn and Mn3N2 phases coexist, which leads to a reduction of the total magnetization per Mn atom due to the presence of metallic Mn. For small Mn layer thickness (tm<0.86 nm), where noncontinuous Mn3N2 layers are formed, the magnetization decreases noticeably due to the superparamagnetic size limit. It has been found that the best conditions for the stabilization of the ferromagnetism in this system occur when both, the manganese-rich and the silicon nitride layers, are continuous and with similar thickness, close to 3.5 nm.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Cd Deposition by sputtering
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals

Structures and magnetic properties of p-type Mn:TiO2 dilute magnetic semiconductor thin films

Xinyu Li, Shuxiang Wu, Ping Hu, Xiangjun Xing, Yajing Liu, Yunpeng Yu, Mei Yang, Jingquan Lu, Shuwei Li, and Wen Liu

J. Appl. Phys. 106, 043913 (2009); http://dx.doi.org/10.1063/1.3204493 (5 pages) | Cited 3 times

Online Publication Date: 26 August 2009

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The behavior of p-type conductivity in Mn-doped TiO2 films grown on LaAlO3 substrates by plasma-assisted molecular beam epitaxy has been investigated. Raman scattering, x-ray photoelectron spectroscopy, and x-ray diffraction studies indicate that the films are single phase, and Mn is successfully doped into the TiO2 matrix. Semiconducting behavior with p-type carriers was confirmed by Hall-effect measurements. The structural and electrical investigations demonstrate that the ferromagnetism observed at room temperature is an intrinsic property of the Mn:TiO2 films, and does not originate from any secondary phase. The magnetic properties of Ti1−xMnxO2 might be related to the formation of acceptor bound magnetic polarons, in which the spins of the holes and manganese are aligned via exchange interaction.
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68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
61.72.up Other materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.30.Hv Other nonmetallic inorganics

Thermally activated domain wall depinning in thin strips with high perpendicular magnetocrystalline anisotropy

E. Martinez, L. Lopez-Diaz, O. Alejos, and L. Torres

J. Appl. Phys. 106, 043914 (2009); http://dx.doi.org/10.1063/1.3204496 (5 pages) | Cited 10 times

Online Publication Date: 26 August 2009

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A theoretical analysis on domain wall dynamics along thin ferromagnetic strips with high perpendicular magnetocrystalline anisotropy driven by both magnetic fields and spin-polarized currents is reported. The domain wall depinning from a constriction is characterized both at zero and at room temperature for different values of the nonadiabatic parameter. The results indicate that engineering of pinning sites in thin strips of high perpendicular anisotropy provides an efficient pathway to achieve both high stability against thermal fluctuations and low current-induced domain wall depinning and, therefore, it can find application on designing memory devices driven by static currents.
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75.60.Ch Domain walls and domain structure
75.30.Gw Magnetic anisotropy
72.25.-b Spin polarized transport

Magnetic properties of sonochemically synthesized CoCr2O4 nanoparticles

Dimple P. Dutta, J. Manjanna, and A. K. Tyagi

J. Appl. Phys. 106, 043915 (2009); http://dx.doi.org/10.1063/1.3204659 (4 pages) | Cited 8 times

Online Publication Date: 26 August 2009

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Cobalt chromite (CoCr2O4) is a potential multiferroic material. In order to understand the temperature dependent magnetic transitions on particle morphology, here we prepared CoCr2O4 nanoparticles by sonochemical technique. We used powder x-ray diffraction, transmission electron microscopy, selected area electron diffraction, superconducting quantum interference device magnetometer, and ac susceptibility measurement techniques for characterization. The low-temperature magnetic behavior of CoCr2O4 nanoparticles have been investigated in more detail. While the bulk CoCr2O4 exhibits two magnetic transitions viz., Tc ≈ 98 K and Ts ≈ 26 K, the nanoparticles here showed a Tc ≈ 84 K and Ts ≈ 25 K. We tentatively attribute this shift in Tc to finite size effects.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Gg Ferrimagnetics
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

The effect of tilted edges on the shape anisotropy and stray field coupling of uniformly magnetized rectangular elements

S. Pütter, N. Mikuszeit, E. Y. Vedmedenko, and H. P. Oepen

J. Appl. Phys. 106, 043916 (2009); http://dx.doi.org/10.1063/1.3169781 (6 pages) | Cited 3 times

Online Publication Date: 27 August 2009

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The influence of tilted edges on the magnetostatic properties of uniformly magnetized thin rectangular elements is studied. To calculate the magnetostatic energy, the Poisson equation is solved. The shape of the magnetic element is approximated by horizontally assembled thin cuboids and the solutions of Rhodes and Rowlands [Proc. Leeds Phil. Soc. 6, 191 (1954)] are utilized. A second approach is the straightforward integration of the Poisson equation taking into account the trapezoidal shape of the side faces due to the tilted edges. For an adequate number of cuboids, both methods agree very well. It is found that the shape anisotropy of a single magnetic element with tilted edges is reduced compared to that of an ideal cuboid. For a two element system the shape anisotropy competes with the magnetostatic interaction favoring a magnetization orientation parallel to the connecting line of the elements. If the elements are oriented in-line with their short axes, the easy magnetization axis switches at a critical distance between the elements. This distance increases when the elements have tilted edges.
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75.30.Gw Magnetic anisotropy
75.40.Mg Numerical simulation studies

A thermal memory cell

J. Dolinšek, M. Feuerbacher, M. Jagodič, Z. Jagličić, M. Heggen, and K. Urban

J. Appl. Phys. 106, 043917 (2009); http://dx.doi.org/10.1063/1.3207791 (5 pages) | Cited 4 times

Online Publication Date: 28 August 2009

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We present a concept of a new kind of memory element, a thermal memory cell, where a byte of digital information can be stored into the storage medium by pure thermal manipulation. Thermal inscription of information employs a specific temperature-time profile that involves continuous cooling and isothermal waiting time periods in the absence of any external magnetic or electric field. Our storage media are magnetically frustrated solids. We succeeded to thermally write arbitrary American Standard Code for Information Interchange characters into the Taylor-phase T-Al3(Mn,Fe) complex intermetallic compound and the Cu–Mn canonical spin glass. Besides for data storage, the concept may be employed for secure data transfer and for retrieving cosmological information from extraterrestrial dust particles.
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75.50.Lk Spin glasses and other random magnets
75.40.-s Critical-point effects, specific heats, short-range order

The magnetothermal behavior of mixed-valence Eu3O4

Kyunghan Ahn, V. K. Pecharsky, and K. A. Gschneidner, Jr.

J. Appl. Phys. 106, 043918 (2009); http://dx.doi.org/10.1063/1.3204662 (6 pages)

Online Publication Date: 31 August 2009

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The mixed-valence compound Eu3O4 was prepared by heating an equimolar mixture of EuO and Eu2O3 at 1800 °C for 30 h in a sealed tungsten crucible. Room temperature x-ray powder diffraction measurements showed that Eu3O4 is single phase. Magnetic measurements on polycrystalline Eu3O4 are in good agreement with the results reported previously. The heat capacity of Eu3O4 from ∼ 2 to 300 K was not reported in the past. The magnetocaloric effect in Eu3O4 was measured for different applied magnetic fields. The magnetic entropy change (−ΔSmag) calculated from heat capacity data of Eu3O4 is approximately 12.7 J/kg K at 6.5 K for a magnetic field change (ΔB) of 5 T. The adiabatic temperature change (ΔTad) in Eu3O4 at 7 K is about 7.0 K for a ΔB of 5 T. Also, the magnetic entropy change (−ΔSmag) calculated from magnetization data in Eu3O4 is approximately 13.6 J/kg K at 6.3 K for a magnetic field change (ΔB) of 5 T, which is slightly higher than that from the heat capacity data, but is within experimental error. A metamagnetic transition was observed between 0.3 and 0.5 T, however, some antiferromagnetic correlations appear to exist in the magnetically induced ferromagnetic phase at B>3 T.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
65.40.Ba Heat capacity
65.40.gd Entropy
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