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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Magnetic properties of L10 FePt and FePt:Ag nanocluster films

Yingfan Xu, Z. G. Sun, Y. Qiang, and D. J. Sellmyer

J. Appl. Phys. 93, 8289 (2003); http://dx.doi.org/10.1063/1.1556256 (3 pages) | Cited 20 times

Online Publication Date: 9 May 2003

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A sputtering gas-aggregation technique has been used to prepare FePt and FePt:Ag nanocluster films. The cluster size was controlled in a range from 3 to 6 nm. FePt cluster films were directly deposited onto Si substrate; FePt:Ag cluster films were fabricated by depositing a FePt cluster layer between a Ag underlayer and overlayer. Nanostructure and magnetic properties of the samples were characterized by x-ray diffraction, transmission electron microscopy, and magnetometry. The high magnetic anisotropy L10 fct phase was realized in the films annealed at a temperature of 550 °C and above. The orientation of clusters is random. The coercivity increases with an increase of annealing temperature; high in-plane and out-of-plane coercivities, exceeding 10 kOe, were achieved in both FePt and FePt:Ag cluster films after annealing. For FePt:Ag films, the coercivity increases with Ag underlayer thickness, tAg, and reaches about 17 kOe at room temperature for tAg=5 nm after annealing at 650 °C for 10 min. The high coercivity is closely correlated with the degree of L10 ordering and nanostructure of the films. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)
75.30.Gw Magnetic anisotropy
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions

Highly oriented nonepitaxially grown L10 FePt films

M. L. Yan, N. Powers, and D. J. Sellmyer

J. Appl. Phys. 93, 8292 (2003); http://dx.doi.org/10.1063/1.1556257 (3 pages) | Cited 50 times

Online Publication Date: 9 May 2003

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A method of preparing nonepitaxially grown, highly textured L10 FePt thin films is described. A nearly perfect (001) texture was obtained by direct deposition of FePt films on Corning 7059 glass substrates and subsequent rapid thermal annealing. The ordering and orientation of the L10-phase FePt grains were controlled by the initial as-deposited film structure, and also by the annealing process. Magnetic measurements reveal large perpendicular anisotropy for these (001) textured films. The substrates and processes used for nonepitaxial growth of L10 ordered FePt films are much more compatible with practical applications than those grown epitaxially. © 2003 American Institute of Physics.
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75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Cd Deposition by sputtering
75.30.Gw Magnetic anisotropy
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology

Room temperature active regenerative magnetic refrigeration: Magnetic nanocomposites

Farhad Shir, Levent Yanik, Lawrence H. Bennett, Edward Della Torre, and Robert D. Shull

J. Appl. Phys. 93, 8295 (2003); http://dx.doi.org/10.1063/1.1556258 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2003

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Nanocomposites have several advantages as a refrigerant for 100–300 K applications compared to the other common methods of assembling a magnetic refrigeration bed, such as a layered thermal bed, or mixing of different magnetic materials. This article discusses the thermodynamics and heat transfer analysis of an ideal and real active magnetic regenerative refrigeration cycle. An algorithm for the choice of optimum parameters is derived. © 2003 American Institute of Physics.
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75.30.Sg Magnetocaloric effect, magnetic cooling
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Wx Nanopowders
81.07.Bc Nanocrystalline materials
65.40.G- Other thermodynamical quantities

Magnetic field induced phase transitions in Gd5(Si1.95Ge2.05) single crystal and the anisotropic magnetocaloric effect

H. Tang, A. O. Pecharsky, D. L. Schlagel, T. A. Lograsso, V. K. Pecharsky, and K. A. Gschneidner

J. Appl. Phys. 93, 8298 (2003); http://dx.doi.org/10.1063/1.1556259 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2003

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Magnetization measurements using a Gd5(Si1.95Ge2.05) single crystal with the magnetic field applied along three crystallographic directions, [001], [010] and [100], were carried out as a function of the applied field (0–56 kOe) at various temperatures (∼5–320 K). The magnetic field (H)–temperature (T) phase diagrams were constructed for the Gd5(Si1.95Ge2.05) single crystal with field along the three directions. A small anisotropy was observed. The magnetocaloric effect was calculated from isothermal magnetization data, and the observed anisotropy correlates with the H–T phase diagrams. The results are discussed in connection with the magnetic field induced martensitic-like structural transition observed in Gd5(Si2Ge2)-type compounds. © 2003 American Institute of Physics.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Gw Magnetic anisotropy
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations

Large magnetoresistance in (La1−xCaxMnO3)1−y:ZrO2 composite

D. Das, A. Saha, S. E. Russek, R. Raj, and D. Bahadur

J. Appl. Phys. 93, 8301 (2003); http://dx.doi.org/10.1063/1.1556260 (3 pages) | Cited 29 times

Online Publication Date: 9 May 2003

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Colossal magnetoresistance (CMR) composite materials have been synthesized to explore the possibility of improving magneto-transport and structural properties in CMR systems. In this work we describe (La1−xCaxMnO3)1−y (LCMO) (ZrO2)y (x≈0.3 and 0.0⩽y⩽0.40 mole %) composites that have been synthesized using a modified (non Pechini type) sol–gel technique. Magnetoresistivity of the composites was evaluated at 5 T field and in the temperature range 5–300 K. The composites show higher magnitude of MR compared to pure LCMO. The MR rises from a base value 76%, for the case y=0, to a maximum value of 93.8%, obtained at y=0.05. dc susceptibility measurements show a distinct ferromagnetic to paramagnetic transition in all composites. The ferromagnetic transition temperature (TC) drops from 225 K in pure LCMO (y=0) to 121 K in y=0.05 and then slowly rises to 157 K as y increases. The plots of zero field cooled susceptibility χZFC (T) and field cooled susceptibility χFC (T) diverge clearly below TC, indicating magnetic irreversibility. The composite exhibits a clear metal–insulator transition (TMI) at or just above the magnetic transition. The peak resistivity ρMI at the metal–insulator transition also exhibits interesting changes. For pure LCMO polycrystals, ρMI=102 Ω cm, but it increases to 228 Ω cm for y=0.05 and then gradually decreases to 1.94 Ω cm for y⩾0.10. The phase evolution in the LCMO:ZrO2 composites was studied by x-ray powder diffraction and correlated to the magnetic and electrical properties. © 2003 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.47.Gk Colossal magnetoresistance
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.60.+g Mixed conductivity and conductivity transitions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
64.75.-g Phase equilibria

Magnetic properties of Nd5SixSn4−x

H. B. Wang, Miryam Elouneg-Jamróz, D. H. Ryan, and Z. Altounian

J. Appl. Phys. 93, 8304 (2003); http://dx.doi.org/10.1063/1.1556271 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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The structure and magnetic properties of Nd5SixSn4−x have been investigated using x-ray diffraction, 119Sn Mössbauer spectroscopy and bulk magnetic techniques. The crystal structure is orthorhombic for x⩽3.5, above which it is tetragonal. The ac-susceptibility shows that the magnetic ordering temperatures of Nd5SixSn4−x increase from 35 to 120 K as x increases. Magnetization data indicate that the Nd moments cannot be ordered ferromagnetically at 5 K and that the magnetic structure must be mixed ferro-antiferromagnetic form as seen in the Nd5SixGe4−x system. The 119Sn Mössbauer spectra of Nd5SixSn4−x at 9 K are dominated by two, sharp hyperfine sextets with fields between 10 and 16 T that increase with x. © 2003 American Institute of Physics.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Effect of Be doping on the properties of GaMnAs ferromagnetic semiconductors

S. Lee, S. J. Chung, I. S. Choi, Sh. U. Yuldeshev, Hyunsik Im, T. W. Kang, W.-L. Lim, Y. Sasaki, X. Liu, T. Wojtowicz, and J. K. Furdyna

J. Appl. Phys. 93, 8307 (2003); http://dx.doi.org/10.1063/1.1556272 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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We have studied two series of molecular beam epitaxy grown Ga1−xMnxAs epilayers with several different Be doping levels. Two Mn concentrations x were chosen for this study: 0.03 and 0.05, and these values were maintained constant in each series. These samples were characterized by using SQUID and magnetotransport measurements. A systematic increase of the Curie temperature TC was observed in SQUID measurements on the series of Ga1−xMnxAs with x=0.03. The resistivity measured at zero magnetic field shows a local maximum near the Curie temperature, reflecting the effects of critical scattering near TC. The observed increase of TC in Ga1−xMnxAs for this low range of x can be explained by the increase of the free carrier concentrations in the system arising from Be doping. However, in the series of Ga1−xMnxAs with the higher concentration of Mn (x=0.05), the measurements reveal that the TC systematically decreases with increasing Be doping level. We discuss this effect in terms of a fundamental limitation of the carrier concentration that can be thermodynamically accommodated by Ga1−xMnxAs epilayers. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ey III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Microstructure and magnetic properties of CoZr thin film

Xiao-Feng Yao, Jian-Ping Wang, Tie-Jun Zhou, and Tow Chong Chong

J. Appl. Phys. 93, 8310 (2003); http://dx.doi.org/10.1063/1.1556273 (3 pages) | Cited 1 time

Online Publication Date: 9 May 2003

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Annealing effects on the microstructure and magnetic properties of CoZr thin films are investigated in this article. It was found that a change in magnetic phase occurs by annealing the as-deposited films at temperatures of above 550 °C for 2 h. A much lower annealing temperature and shorter annealing time are needed to obtain a hard magnetic phase in thin films than in rapidly quenched CoZr bulk samples. Hard magnetic phase Co11Zr2 and ferromagnetic phase Co23Zr6 formed after annealing. All the annealed films show perpendicular magnetic anisotropy. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.Nq Composition and phase identification
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments

Change in entropy at a first-order magnetoelastic phase transition: Case study of Gd5(SixGe1−x)4 giant magnetocaloric alloys

Fèlix Casanova, Xavier Batlle, Amílcar Labarta, Jordi Marcos, Lluís Mañosa, and Antoni Planes

J. Appl. Phys. 93, 8313 (2003); http://dx.doi.org/10.1063/1.1556274 (3 pages) | Cited 8 times

Online Publication Date: 9 May 2003

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The change in entropy, ΔS, at the first-order magnetoelastic phase transition in Gd5(SixGe1−x)4 alloys for x⩽0.5 has been measured with a high-sensitivity differential scanning calorimeter with built-in magnetic field, H. Scaling of ΔS is achieved by changing the transition temperature, Tt, with x and H from 70 to 310 K. Tt is thus the relevant parameter in determining the giant magnetocaloric effect in these alloys. The calorimetric determination of the change in entropy is also in agreement with the indirect calculation obtained from the magnetization curves measured up to 23 T using both the Clausius–Clapeyron equation and the Maxwell relation. A simple phenomenological model based on the magnetization curves accounts for these results. © 2003 American Institute of Physics.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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