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1 Apr 2009

Volume 105, Issue 7, Articles (07xxxx)

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back to top Magneto-Optic, Magneto-Elastic, and Magneto-Caloric Materials

Effect of substitution of Co for Fe on the magnetic hysteresis loss and the refrigerant capacity in the La0.5Pr0.5Fe11.5Si1.5 compounds

Jun Shen, Yang-Xian Li, Feng-Xia Hu, and Ji-Rong Sun

J. Appl. Phys. 105, 07A901 (2009); http://dx.doi.org/10.1063/1.3055188 (3 pages) | Cited 4 times

Online Publication Date: 30 January 2009

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Magnetic hysteresis loss and refrigerant capacity of the NaZn13-type La0.5Pr0.5Fe11.5−xCoxSi1.5 (0 ⩽ x ⩽ 1.0) compounds have been investigated. The substitution of Co in the La0.5Pr0.5Fe11.5Si1.5 causes the order of phase transition at TC to change from first order to second order at x = 0.6. Although the magnetic entropy change decreases with increasing Co concentration, the hysteresis loss at TC also reduces remarkably from 94.8 J/kg for x = 0 to 1.8 J/kg for x = 0.4 because an increase in Co content can weaken the itinerant electron metamagnetic transition. The effective refrigerant capacity remains at a high value ranging from 355 to 433 J/kg for a field change of 0–5 T as x varies from 0 to 1.0.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

A first-principles study on the magnetocaloric compound MnFeP2/3Si1/3

X. B. Liu and Z. Altounian

J. Appl. Phys. 105, 07A902 (2009); http://dx.doi.org/10.1063/1.3056408 (3 pages) | Cited 4 times

Online Publication Date: 2 February 2009

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The electronic structure and magnetic properties for MnFeP2/3Si1/3 with a hexagonal Fe2P-type structure have been studied by a first-principle density functional theory calculation. The calculated magnetic moments for Fe and Mn are 1.35 and 2.89 μB, respectively, leading to a total magnetization of 4.15 μB per formula unit due to the small negative moments of P and Si atoms. The total energy calculations show that the Si atoms prefer to occupy the 2c site rather than the 1b site and increase the moment of Fe while decreasing the moment of Mn. The nearest Mn–Fe exchange coupling interaction (JMn–Fe = 1.33 mRy) is much stronger than for Fe–Fe (JFe–Fe = −0.16 mRy) and Mn–Mn atomic pair (JFe–Fe = −0.53 mRy) interactions. The competed exchange interactions are responsible for the field induced first order magnetic transition and the large magnetocaloric effect.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Et Exchange and superexchange interactions
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Alkanethiol induced changes in the magnetotransport properties of Co/Au bilayers

B. Knaus, S. Garzon, and T. M. Crawford

J. Appl. Phys. 105, 07A903 (2009); http://dx.doi.org/10.1063/1.3056153 (3 pages) | Cited 1 time

Online Publication Date: 3 February 2009

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We demonstrate that chemisorption of a dodecanethiol (C12H25SH) self-assembled monolayer on the surface of a Au film alters the coercivity Hc of an underlying Co film, as measured using the planar Hall effect. Changes in Hc occur over a time scale of hours, and only when the thiolated devices are biased with perpendicular magnetic fields. While vacuum-stored samples show larger changes in Hc than those stored under ambient conditions, sample-sample variability persists. We hypothesize that the coercivity shifts are caused by magnetostatic fields originating at the Au-thiol interface, which affect the Co domain structure during magnetization reversal.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.43.-h Chemisorption/physisorption: adsorbates on surfaces
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

First-order magnetic phase transition in FeRh–Pt thin films

W. Lu, N. T. Nam, and T. Suzuki

J. Appl. Phys. 105, 07A904 (2009); http://dx.doi.org/10.1063/1.3065973 (3 pages) | Cited 5 times

Online Publication Date: 4 February 2009

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The first-order antiferromagnetic/ferromagnetic phase transition in ordered FeRh100−XPtX (0≦X≦15) thin films grown onto MgO(100) substrate was investigated by temperature dependent magnetization measurements. It is shown that the phase transition temperature increases with increasing Pt content. The field dependence of transition temperature was also measured and a shift of −8 to −3.3 K/T is observed for FeRh100−XPtX thin films with increasing Pt contents. In addition, the entropy changes associated with the magnetic phase transition were studied, and it can be proposed that the change in electronic entropy associated with the magnetic moment of Rh atoms is the main mechanism for the first-order magnetic phase transition in ordered FeRh-based alloys.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.30.Cr Saturation moments and magnetic susceptibilities

Enhanced magnetization of CuCr2O4 thin films by substrate-induced strain

Jodi M. Iwata, Rajesh V. Chopdekar, Franklin J. Wong, Brittany B. Nelson-Cheeseman, Elke Arenholz, and Yuri Suzuki

J. Appl. Phys. 105, 07A905 (2009); http://dx.doi.org/10.1063/1.3058612 (3 pages) | Cited 1 time

Online Publication Date: 4 February 2009

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The first synthesis of epitaxial spinel CuCr2O4 thin films is reported, which exhibit enhanced magnetization in excess of 200% of the accepted bulk value when grown on single-crystal (110) MgAl2O4 substrates. Bulk CuCr2O4 is a ferrimagnetic insulator with a low net magnetic moment of 0.5μB due to its tetragonal unit cell with a c/a ratio of 1.29 and frustrated moment configuration. It is shown that through epitaxial growth and substrate-induced strain, it is possible to enhance the magnetization of these films by reducing the tetragonality of its unit cell which, in turn, effectively decreases magnetic moment frustration allowing for a greater net moment.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.40.-s Critical-point effects, specific heats, short-range order
68.55.aj Insulators

Local magnetic properties of Y12Co5Bi and Gd12Co5Bi studied by muon spin relaxation

M. Egilmez, K. H. Chow, W. A. MacFarlane, A. Mar, I. Fan, A. Mansour, D. Schick-Martin, J. Jung, A. V. Tkachuk, B. Hitti, and D. Arseneau

J. Appl. Phys. 105, 07A906 (2009); http://dx.doi.org/10.1063/1.3059373 (3 pages)

Online Publication Date: 4 February 2009

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The recently discovered (RE)12Co5Bi (where RE is a rare earth element) system has rich magnetic phase diagrams. We applied muon spin relaxation to study the local magnetism in polycrystalline samples of Y12Co5Bi and Gd12Co5Bi. Our results indicate a magnetic transition at around 100 K for Gd12Co5Bi. By contrast, Y12Co5Bi does not show a magnetic transition as expected since Y3+ does not contain any f electrons. These results are consistent with the dc susceptibility measurements. We also estimate and discuss the fluctuation rates in the high temperature paramagnetic regime for Gd12Co5Bi.
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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
75.20.En Metals and alloys
76.75.+i Muon spin rotation and relaxation

Thiol-capped ferromagnetic Au nanoparticles investigated by Au L3 x-ray absorption spectroscopy

J. S. Garitaonandia, E. Goikolea, M. Insausti, M. Suzuki, N. Kawamura, H. Osawa, I. Gil del Muro, K. Suzuki, J. D. Cashion, C. Gorria, F. Plazaola, and T. Rojo

J. Appl. Phys. 105, 07A907 (2009); http://dx.doi.org/10.1063/1.3059609 (3 pages) | Cited 5 times

Online Publication Date: 5 February 2009

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Different dodecanethiol capped Au nanoparticles (NP) with similar sizes ( ∼ 2 nm) but different ferromagnetic signals at room temperature have been investigated by means of x-ray absorption spectroscopy at the Au L3-edge. The reversion of the x-ray magnetic circular dichroism signal with the change of sign of the external applied magnetic field confirms the location of the magnetism at the Au atoms. In comparison with the Au foil, all the samples present accentuated white lines at the x-ray absorption near-edge structure (XANES) indicating generation of 5d holes in the Au atoms located at surface of the NPs as consequence of a localized charge transfer from the Au surface atoms to the S atoms of the capping agent. XANES spectra reflect differences among the electronic structure of the Au NPs which are compared with the observed different macroscopic magnetic signals.
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73.22.-f Electronic structure of nanoscale materials and related systems
75.50.Cc Other ferromagnetic metals and alloys
78.70.Dm X-ray absorption spectra
78.20.Ls Magneto-optical effects
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
75.50.Tt Fine-particle systems; nanocrystalline materials

Magnetic, transport, and magnetocaloric properties of double perovskite oxide LaCaMnCoO6

Rabindra Nath Mahato, K. Kamala Bharathi, K. Sethupathi, V. Sankaranarayanan, R. Nirmala, A. K. Nigam, and Jagat Lamsal

J. Appl. Phys. 105, 07A908 (2009); http://dx.doi.org/10.1063/1.3059592 (3 pages) | Cited 2 times

Online Publication Date: 5 February 2009

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Magnetic, magnetoresistive, and magnetocaloric properties of a novel double perovskite oxide, namely, LaCaMnCoO6 have been studied. Polycrystalline sample of LaCaMnCoO6 has been synthesized by sol-gel technique. It has cubic crystal structure (space group Fmmathm) at room temperature. The temperature variation in magnetization reveals a steep increase in magnetization around 168 K (TC). The magnetization does not even saturate at 5 K and a magnetic moment of 0.7μB/f.u. is obtained at 5 K in an applied field of 50 kOe. The electrical resistivity measurement indicates that the material is semiconducting-like in the temperature range of ∼ 300–50 K and below ∼ 50 K the sample becomes insulating. A maximum magnetoresistance (MR) of about 8% is found at 200 K in an applied field of 7 T and MR has a negative sign. The magnetocaloric effect is calculated from the magnetization versus temperature data and a maximum magnetic entropy change of 3.1 J/kg K for a field change of 11 kOe is obtained near TC. Thus a moderate magnetocaloric effect is achieved in rather low magnetic fields.
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75.30.Sg Magnetocaloric effect, magnetic cooling
72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Fn Inorganic compounds
75.30.Cr Saturation moments and magnetic susceptibilities
72.80.Sk Insulators

Re-entrant ferromagnet PrMn2Ge0.8Si1.2: Magnetocaloric effect

J. L. Wang, S. J. Campbell, R. Zeng, C. K. Poh, S. X. Dou, and S. J. Kennedy

J. Appl. Phys. 105, 07A909 (2009); http://dx.doi.org/10.1063/1.3059610 (3 pages) | Cited 7 times

Online Publication Date: 5 February 2009

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The structural and magnetic properties of the re-entrant ferromagnet PrMn2Ge0.8Si1.2 have been investigated by various experimental methods. Similar to the canonical re-entrant ferromagnet SmMn2Ge2, multiple magnetic phase transitions have been detected in PrMn2Ge0.8Si1.2 over the temperature range from 10 to 550 K with re-entrant ferromagnetism occurring around ∼ 54 K. The magnetocaloric effect has been measured in terms of the isothermal magnetocaloric entropy change and found to be positive at the re-entrant ferromagnetic transition with a maximum value of around 1.9 J/kg K at 58 K for a magnetic field change of 0–3 T. On the other hand, the entropy change becomes negative ( ∼ −0.5 J/kg K) at the antiferromagnetic to ferromagnetic transition for the same field change.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Cc Other ferromagnetic metals and alloys
61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetocaloric effect in Fe–Zr–B–M (M = Mn, Cr, and Co) amorphous systems

Y. K. Fang, C. C. Yeh, C. C. Hsieh, C. W. Chang, H. W. Chang, W. C. Chang, X. M. Li, and W. Li.

J. Appl. Phys. 105, 07A910 (2009); http://dx.doi.org/10.1063/1.3054369 (3 pages) | Cited 4 times

Online Publication Date: 6 February 2009

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The magnetocaloric effect (MCE) of the amorphous Fe–Zr–B–M (M = Mn, Cr, and Co) ribbons has been investigated. The MCEs of the Fe90−xZr10Bx (x = 5, 10, 15, and 20) ribbons are enhanced with small amounts of boron addition. Furthermore, the Curie temperature of the specimens can be decreased to be about room temperature with appropriate Mn and Cr substitutions, but the MCE performance of the specimens drops only slightly. It is also found that the magnetic entropy change of the Co-substitution series of Fe85−yZr10B5Coy ribbons almost remains constant although the Curie temperature is increased to be about 400 K for y = 5. Therefore, for the application of MCE refrigeration at above room temperature, the Fe85−yZr10B5Coy ribbons are preferred due to the constant MCE and the high refrigeration capacity of about 90 J/kg at the magnetic field change of 10 kOe. Moreover, the field dependence of the magnetic entropy change exhibits power dependence for all the studied specimens. In the ferromagnetic range, the exponent is close to 1. In the paramagnetic regime, well above the Curie temperature, the exponent is 2, in agreement with the Curie–Weiss law.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.20.En Metals and alloys
75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials

Magnetic ordering in the rare earth intermetallic compound Tb2Ti3Ge4: Magnetization and neutron diffraction studies

S. K. Malik, Jagat Lamsal, R. L. de Almeida, S. Quezado, W. B. Yelon, V. O. Garlea, A. V. Morozkin, and R. Nirmala

J. Appl. Phys. 105, 07A911 (2009); http://dx.doi.org/10.1063/1.3063073 (3 pages)

Online Publication Date: 6 February 2009

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Magnetization and neutron diffraction studies on a polycrystalline Tb2Ti3Ge4 sample (orthorhombic Sm5Ge4-type structure, space group Pnma, No. 62) have been carried out. This compound is found to order antiferromagnetically at ∼ 18 K (TN). The magnetization (M) versus field (H) isotherms obtained at 2, 3, 5, and 10 K indicate a field-induced antiferromagnetic to ferromagnetic transition in fields of the order of 0.5 T. The saturation magnetization value at 2.5 K (M extrapolated to 1/H→0) is only ∼ 5.6μB/Tb3+, suggesting the possible presence of crystal field effects with or without a persisting antiferromagnetic component. Neutron powder diffraction data at 10 K confirm the existence of a magnetic long range order. Modeling of the magnetic scattering reveals a complex and incommensurate antiferromagnetic spin structure below TN.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.70.Ch Crystal and ligand fields
75.50.Ee Antiferromagnetics

Effect of a forming field on the magnetic and structural properties of thin Fe–Ga films

N. A. Morley, A. Javed, and M. R. J. Gibbs

J. Appl. Phys. 105, 07A912 (2009); http://dx.doi.org/10.1063/1.3059612 (3 pages) | Cited 9 times

Online Publication Date: 6 February 2009

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The structural, magnetic, and magnetostrictive properties of 75 nm Fe100−xGax films (0 ⩽ x ⩽ 30) have been studied to determine how a forming field during growth affects these properties. Two film sets were grown using a cosputtering-evaporation technique with and without a forming field of 65 kA m−1. Using x-ray diffraction, the texture, lattice parameter, and the grain size were determined. An out-of-plane ⟨110⟩ texture was found for all films. The magnetization loops were measured on a magneto-optic Kerr effect magnetometer, from which the anisotropy symmetry was inferred from the remanent magnetization. It was found that the forming field produced a pronounced uniaxial anisotropy. The effective magnetostriction constant was measured using the Villari effect. The effective magnetostriction constant was compared with that calculated for a polycrystalline film with ⟨110⟩ out-of-plane texture using bulk constants, and the results are discussed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.55.jm Texture
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
78.66.Bz Metals and metallic alloys

Stress dependent magnetostriction in highly magnetostrictive Fe100−xGax, 20<x<30

A. E. Clark, J.-H. Yoo, J. R. Cullen, M. Wun-Fogle, G. Petculescu, and A. Flatau

J. Appl. Phys. 105, 07A913 (2009); http://dx.doi.org/10.1063/1.3058685 (3 pages) | Cited 4 times

Online Publication Date: 9 February 2009

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Saturation magnetostriction measurements along the [100] axis of Fe100−xGax single crystal rods ( ∼ 25×6 mm diameter) were observed to have a linear dependence on [100] applied compressive stresses for 20<x<30. This is not expected from linear magnetoelastic theory and indeed is negligible for x = 19.5. An expansion of the magnetoelastic theory to include third order elastic terms reveals the existence of a term that gives rise to a stress dependent [100] magnetostriction. For x = 20.9 and 29.5, the stress T dependencies of the saturation magnetostrictions were found to be 0.136×10−6T MPa−1 and 0.281×10−6T MPa−1, respectively. Values of the third order elastic constants, c3’s, calculated from these values agree both in sign and magnitude with those obtained from stress dependent measurements of Young’s moduli and Poisson’s ratios. In sum, we conclude that the Fe100−xGax magnetostriction for 0<x<30 can be attributed to a simple homogenous single domain magnetoelastic mechanism.
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75.50.Bb Fe and its alloys
75.80.+q Magnetomechanical effects, magnetostriction

Electrical transport and magnetism in Mo-substituted R2Ti3Ge4 (R = Tb,Er) compounds

R. Nirmala, K. Hima Nagamanasa, P. A. Bhobe, Jagat Lamsal, and A. K. Nigam

J. Appl. Phys. 105, 07A914 (2009); http://dx.doi.org/10.1063/1.3065977 (3 pages)

Online Publication Date: 9 February 2009

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The effect of Mo substitution at Ti site of orthorhombic Sm5Ge4-type R2Ti3Ge4 compounds on the magnetic and electrical transport properties has been studied. The Tb2Ti3−xMoxGe4 (x = 0.3,0.75) and Er2Ti2.7Mo0.3Ge4 compounds have been synthesized and it is found that these compounds retain parent crystal structure at room temperature (space group Pnma, No. 62). Mo substitution decreases the antiferromagnetic ordering temperature (TN) of Tb2Ti3Ge4 compound from ∼ 18 to ∼ 13 and ∼ 10 K, respectively, for x = 0.3 and 0.75. The Er2Ti2.7Mo0.3Ge4 compound shows a tendency to order at ∼ 2 K, whereas the parent Er2Ti3Ge4 is magnetically ordered at 3 K. Magnetization versus field data of Tb2Ti3−xMoxGe4 (x = 0.3,0.75) reveal soft ferromagnetic nature. The metamagnetic transition that is present in parent Tb2Ti3Ge4 is found to disappear with Mo substitution. Magnetization value reaches ∼ 6.2μB/Tb3+ at 2 K in fields of 8 T, indicating incomplete ferromagnetic ordering with or without an antiferromagnetic component. Electrical resistivity of the Tb-based compounds has a linear variation with temperature from 300 to ∼ 50 K and shows a prominent slope change at temperatures much above TN, supporting the presence of competing short range ferromagnetic interactions.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
61.66.Fn Inorganic compounds
75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Et Exchange and superexchange interactions

Crystal structure and magnetic transition of MnFePGe compound prepared by spark plasma sintering

M. Yue, Z. Q. Li, X. L. Wang, D. M. Liu, J. X. Zhang, and X. B. Liu

J. Appl. Phys. 105, 07A915 (2009); http://dx.doi.org/10.1063/1.3056157 (3 pages) | Cited 4 times

Online Publication Date: 11 February 2009

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The crystal structure and magnetic transition were studied for the bulk Mn1.1Fe0.9P0.8Ge0.2 compound prepared by a simple blending and subsequent spark plasma sintering route. X-ray diffraction analysis and refinement show that the compound crystallizes in the hexagonal Fe2P-type structure, in which the Mn atoms occupy all the 3g sites and some 3f sites, the Fe atoms occupy the rest of the 3f sites, and P and the Ge atoms randomly occupy the 2c and 1b sites. Magnetic measurement indicates that the Curie temperature TC is at 253 K and the thermal hysteresis of M-T curves at TC upon heating and cooling, a signature of a first-order magnetic phase transition, is about 15 K. The maximum magnetic entropy change of the compound reaches as high as 49.2 J/kg K in a field change from 0 to 5 T at 253 K, while the adiabatic temperature change of the compound reaches only 1.2 K in a field change from 0 to 1.5 T at the same temperature.
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61.66.Dk Alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
64.70.kd Metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.gd Entropy

Influence of the substitution of Cu for Si on magnetic entropy change and hysteresis loss in LaFe11.7(Si1−xCux)1.3 compounds

B. Gao, F. X. Hu, J. Wang, J. Shen, J. R. Sun, and B. G. Shen

J. Appl. Phys. 105, 07A916 (2009); http://dx.doi.org/10.1063/1.3063067 (3 pages) | Cited 3 times

Online Publication Date: 11 February 2009

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The magnetic properties, magnetic entropy change, and hysteresis loss in LaFe11.7(Si1−xCux)1.3 compounds were investigated. It was found that the compounds retain the cubic NaZn13 structure when the substitution of Cu reaches 20%. With increasing Cu content from x = 0 to 0.2, the Curie temperature TC increases from 185 to 200 K, while lattice parameter decreases from 11.475 to 11.468 due to the smaller atomic radius of Cu than Si. Metamagnetic behavior becomes weaker and magnetic entropy change |ΔS| drops with raising Cu content. However, |ΔS| still remains a large value, ∼ 20 J/kg K, when x reaches 0.2. An attractive feature is that both thermal and magnetic hysteresis can be remarkably reduced by introducing Cu. The maximum hysteresis loss at TC drops from 74.1 to 0 J /kg when the substitution of Cu for Si increases from 0% to 20%.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.66.Dk Alloys

The magnetocaloric effect in materials with a second order phase transition: Are TC and Tpeak necessarily coincident?

V. Franco, A. Conde, M. D. Kuz’min, and J. M. Romero-Enrique

J. Appl. Phys. 105, 07A917 (2009); http://dx.doi.org/10.1063/1.3063666 (3 pages) | Cited 18 times

Online Publication Date: 12 February 2009

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Using the Arrott–Noakes equation of state it is shown that the Curie point (TC) and the temperature where the magnetic entropy change is maximum (Tpeak) coincide only in the mean field approximation, but the Heisenberg model implies that Tpeak>TC even for homogeneous materials. The distance between Tpeak and TC increases with applied magnetic field following a power law. In both cases, TC corresponds to a singular point in the temperature dependence of the magnetic entropy change. The field dependence of the magnetic entropy change is exactly the same at the Curie temperature and at the temperature of the peak.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
65.40.gd Entropy
75.10.Jm Quantized spin models, including quantum spin frustration

Magnetocaloric effect and spin reorientation transition in single-crystal Er2(Co0.4Fe0.6)17

M. Ilyn, A. V. Andreev, V. Zhukova, A. Zhukov, A. Tishin, and J. Gonzalez

J. Appl. Phys. 105, 07A918 (2009); http://dx.doi.org/10.1063/1.3063669 (3 pages) | Cited 3 times

Online Publication Date: 12 February 2009

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Magnetic and magnetocaloric properties of single crystal Er2(Co0.4Fe0.6)17 were investigated. First order spin reorientation phase transition was observed at 272 K. Magnetic easy-axis anisotropy was found below this temperature and the easy-plane one above. Magnetocaloric effect accompanying field induced first order magnetic reorientation has been measured directly. It reaches −0.25 and 0.15 K, respectively, provided that the field is perpendicular to the easy-magnetization direction. These values were satisfactorily compared with thermodynamic calculations.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Gw Magnetic anisotropy

Influence of the demagnetizing field on the determination of the magnetocaloric effect from magnetization curves

R. Caballero-Flores, V. Franco, A. Conde, and L. F. Kiss

J. Appl. Phys. 105, 07A919 (2009); http://dx.doi.org/10.1063/1.3067463 (3 pages) | Cited 9 times

Online Publication Date: 12 February 2009

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The influence of the demagnetizing factor (N) on the magnetic entropy change (ΔSM) curves is studied for materials with a second order phase transition. For this purpose, a soft magnetic amorphous ribbon is measured for different orientations of the magnetic field with respect to the plane of the sample. For temperatures below the Curie temperature (TC), the increase in N causes a decrease in ΔSM, while for temperatures above TC no change in the shape of the curves has been found for the different orientations, as expected. In order to eliminate this influence of N and compare the ΔSM(T) curves for samples with different shapes, the recently proposed universal curve for the magnetocaloric effect can be used.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Kj Amorphous and quasicrystalline magnetic materials
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Mössbauer spectroscopy study on the magnetic transition in Mn1.1Fe0.9P0.8Ge0.2

X. B. Liu, Z. Altounian, D. H. Ryan, Ming Yue, Zhiqiang Li, Danmin Liu, and Jiuxing Zhang

J. Appl. Phys. 105, 07A920 (2009); http://dx.doi.org/10.1063/1.3067496 (3 pages) | Cited 4 times

Online Publication Date: 12 February 2009

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The magnetic transition has been studied in Mn1.1Fe0.9P0.8Ge0.2 by magnetic measurements and 57Fe Mössbauer spectroscopy. The alloy crystallizes in the hexagonal Fe2P-type structure with lattice constants of a = 6.0476(4) Å and c = 3.4766(7) Å. Both bulk magnetization measurements and Mössbauer spectroscopy show that the as-prepared sample has a significantly lower transition temperature on first cooling (TC1 ≈ 200 K) than after it has undergone thermal cycling to 20 K (TC20 K = 240 K). The behavior of the material stabilizes after the first cooling/heating cycle and no further changes are observed in TC. Working with a stabilized sample, we find that the temperature dependence of the hyperfine field, Bhf(T), is more rapid than that predicted by a simple mean field Brillouin function, and in addition, Bhf(T) shows a thermal hysteresis of 10 K upon cooling versus heating. These results show that the magnetic transition at TC is definitely first order and suggest that there is an additional irreversible magnetostructural change during the first cooling process of the as-prepared sample.
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76.80.+y Mössbauer effect; other γ-ray spectroscopy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.66.Dk Alloys
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Influence of annealing and phase decomposition on the magnetostructural transitions in Ni50Mn39Sn11

W. M. Yuhasz, D. L. Schlagel, Q. Xing, K. W. Dennis, R. W. McCallum, and T. A. Lograsso

J. Appl. Phys. 105, 07A921 (2009); http://dx.doi.org/10.1063/1.3067855 (3 pages) | Cited 2 times

Online Publication Date: 13 February 2009

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Magnetic and structural transitions in the Ni50Mn50−xSnx (x = 10–25) ferromagnetic shape memory alloys are currently of interest. As in Ni–Mn–Ga, these alloys feature high-temperature austenite and low-temperature martensite phases, where the magnetic state is strongly composition dependent. To study the role of chemical ordering in fine-tuning their magnetostructural properties, they were first annealed for 4 weeks/1223 K to achieve structural and compositional homogeneity, and were then further annealed for 1 week ( ∼ 150 K below the reported B2 to L21 transition) at 773 K to increase the degree of chemical ordering. For x = 11, this anneal resulted in a dramatic change in the magnetic ordering temperature. Following the 1223 K anneal, the sample exhibited ferromagnetic ordering at 140 K. After the 773 K anneal, the ferromagnetic transition is at 350 K, a characteristic of the ferromagnetic austenite phase with 15<x<25. Consistent with the magnetization data, transmission electron microscopy examination confirms that the alloy decomposed into two phases with x = 20 and 1. From this result one can conclude that the martensitic transformation occurs only in those compositions where the single phase L21 has been retained in a metastable state on cooling.
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81.40.Gh Other heat and thermomechanical treatments
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.kd Metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Magnetostriction and texture relationships in annealed galfenol alloys

Eric M. Summers, Rob Meloy, and Suok-Min Na

J. Appl. Phys. 105, 07A922 (2009); http://dx.doi.org/10.1063/1.3067849 (3 pages) | Cited 5 times

Online Publication Date: 19 February 2009

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An investigation into the relationship between the measured bulk magnetostriction in rolled galfenol alloy sheet and the measured texture components was conducted. Galfenol rolled sheet was prepared using different texture annealing parameters such as temperature (1000–1300 °C), cooling rate, and dwell time (1–24 h), with their saturation magnetostrictions measured, followed by electron backscattered diffraction to determine the degree of texture that each sample possessed. The dominate orientation in all samples analyzed was the {011}〈100〉, along the desired η-fiber. Measurement results indicate that as the η-fiber texture improves the bulk magnetostriction increases in a linear fashion with a maximum strain value of 154 ppm measured for sheet samples containing 45 area % η-fiber texture.
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Gh Other heat and thermomechanical treatments
79.20.Hx Electron impact: secondary emission
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Soft and hard elastic moduli of Galfenol transduction elements (invited)

M. Wun-Fogle, J. B. Restorff, and A. E. Clark

J. Appl. Phys. 105, 07A923 (2009); http://dx.doi.org/10.1063/1.3058645 (5 pages) | Cited 4 times

Online Publication Date: 24 February 2009

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In materials with high magnetostriction, e.g., Galfenol (Fe100−xGax), strong magnetoelastic coupling produces a strong dependence of the modulus on the magnetic state of the system. This is manifested in stress-strain curves which depend on the applied magnetic field H. Highly textured free standing zone melt Fe81.6Ga18.4 rods approximately 2 in.×¼ in diameter in both as-grown and stress-annealed conditions were measured; one rod was grown at a faster than normal rate. In addition, an Fe81.6Ga18.4 steel (Ga alloyed with 1003 steel) and an Fe81Al19 rod were measured for comparison. Stress-strain curves at an actively controlled fixed magnetic field were obtained and the modulus at constant H, YH, was determined by numerical differentiation. All curves exhibit a minimum in the modulus at a stress that depends on H. At low and high stresses YH saturates and equals YB, the modulus at constant flux density B. A single domain rotation model originally used to model the magnetization and magnetostriction in these materials was able to capture the major features of the stress-strain behavior and modulus, including the position of the minimum YH and the ΔE effect but did not describe the details accurately. The average YB of five Fe81.6Ga18.4 samples grown at normal rates was 76±3 GPa. YH was highly dependent on sample, field, and stress and varied between 22 and 65 GPa. Magnetomechanical coupling factors k33 were calculated to be ∼ 0.65.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
75.60.Ch Domain walls and domain structure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.40.Gh Other heat and thermomechanical treatments

Magnetocaloric effects in the La(Fe,Si)13 intermetallics doped by different elements

L. Jia, J. R. Sun, J. Shen, Q. Y. Dong, J. D. Zou, B. Gao, T. Y. Zhao, H. W. Zhang, F. X. Hu, and B. G. Shen

J. Appl. Phys. 105, 07A924 (2009); http://dx.doi.org/10.1063/1.3072021 (3 pages) | Cited 4 times

Online Publication Date: 25 February 2009

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The magnetocaloric effects (MCEs) of LaFe13−xSix compounds doped by magnetic rare earths (R = Ce, Pr, and Nd) and transition metal (Co) are analyzed. It is found that varying the contents of R and Fe produces similar effects on the MCE, both of which cause a rapid decrease in ΔS with the increase in TC. The ΔS−TC relations thus obtained coincide with each other fairly well, which indicates the equivalence of substituting R for La and Fe for Si. In contrast, partially replacing Fe by Co leads to a slow decrease in ΔS with TC. It is therefore a promising approach to maintain a large ΔS up to high temperatures. As a comparison with these element-doping compounds, the MCEs of hydrides are also discussed. Although interstitial hydrogen can also keep up a large ΔS to high temperatures, the corresponding hydrides are unfortunately unstable above 150 °C. Based on these analyses, the potential refrigerants made of LaFe13−xSix are proposed to have as low as possible Si content (or high R content) and proper Co content simultaneously.
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75.30.Sg Magnetocaloric effect, magnetic cooling
61.72.jj Interstitials

Synthesis and magnetostriction of TbxPr1−x(Fe0.8Co0.2)1.9 cubic Laves alloys

Y. G. Shi, S. L. Tang, J. Y. Yu, L. Zhai, X. K. Zhang, Y. W. Du, and C. P. Yang

J. Appl. Phys. 105, 07A925 (2009); http://dx.doi.org/10.1063/1.3073849 (3 pages)

Online Publication Date: 26 February 2009

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Polycrystalline magnetostrictive alloys TbxPr1−x(Fe0.8Co0.2)1.9 (0 ≤ x ≤ 0.4) which cannot be obtained under normal pressure were synthesized by high-pressure annealing. Measurements of crystal structure, Curie temperature, magnetization, and magnetostriction were made on TbxPr1−x(Fe0.8Co0.2)1.9 alloys. X-ray diffraction results show that the alloys exhibit C15 cubic Laves phase with MgCu2-type structure. The lattice parameter decreases with increasing Tb concentration, while the Curie temperature increases. Because of the antiparallel magnetic moment of Tb and Pr, the saturation magnetization decreases with increasing Tb concentration. The magnetostriction of Tb0.05Pr0.95(Fe0.8Co0.2)1.9 shows a peak at low magnetic fields, while that of Tb0.4Pr0.6(Fe0.8Co0.2)1.9 exhibits a minimum in the whole range of magnetic fields.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Bb Fe and its alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
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