Giant magnetoresistance near the magnetostructural transition in Gd5(Si1.8Ge2.2)

Morellón, L.; Stankiewicz, Jolanta; García‐Landa, B.; Algarabel, P. A.; Ibarra, M. R.

doi:10.1063/1.122797

Cited by 190 publications

(147 citation statements)

References 23 publications

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“…The variation of magnetization with temperature has shown that in this alloy the Curie point occurs at 110 K compared with 268 K in Gd 5 Si 2 Ge 2 . 10 The variation of magnetization as a function of magnetic field shows that the a axis is the magnetic easy axis, with a magnetocrystalline anisotropy of approximately 8.8ϫ 10 7 J/m 3 and a saturation magnetization of M s = 200 emu/ g ͑which with a density of 7.6 gm/ cm 3 gives M s = 1520 emu/ cm 3 , or 1.52ϫ 10 6 A/m͒. This compares with Gd 5 Si 2 Ge 2 which has the b axis as the easy axis with a lower anisotropy of 4.1ϫ 10 4 J/m 3 and a saturation magnetization of M s = 0.6ϫ 10 6 A/m ͑600 emu/ cm 3 ͒.…”

Section: Discussionmentioning

confidence: 99%

“…A number of pseudobinary compounds R 5 ͑Si x Ge 4−x ͒, where R is La, Lu, Gd, Nd, or Dy, have been investigated by Gschneidner et al 1 The alloy Gd 5 ͑Si x Ge 1−x ͒ 4 which has received much attention recently has several unique properties including a giant magnetocaloric effect, 2 giant magnetoresistance, 3 and giant magnetostriction. 4 Morellon et al 5,6 have investigated phase transitions and the magnetocaloric effect in the alloys with R = Tb and Thuy et al 7 have studied both magnetic properties and magnetocaloric effect in polycrystalline samples with specific compositions Tb 5 ͑Si 2 Ge 2 ͒ and Tb 5 ͑Si 3 Ge 1 ͒.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic anisotropy and phase transitions in single-crystal Tb5(Si2.2Ge1.8)

Han

Snyder

Tang

et al. 2005

Journal of Applied Physics

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The Tb 5 (Si x Ge 4−x ) alloy system has many features in common with the Gd 5 (Si x Ge 4−x )system although it has a more complex magnetic and structural phase diagram. This paper reports on the magnetic anisotropy and magnetic phase transition of single-crystalTb 5 (Si 2.2 Ge 1.8 ) which has been investigated by the measurements of M-H and M-T along the a, b, and c axes. The variation of 1/χ vs T indicates that there is a transition from paramagnetic to ferromagnetic at T c = 110 K. Below this transition temperature M-Hcurves show very strong anisotropy, and it is believed that this is due to the complex spin configuration. M-H measurements at T = 110 K show that the a axis is the easy axis, and that the saturation magnetization is 200 emu/g. The b axis is the hard axis, which needs an external magnetic field much higher than 2 T to saturate the magnetization in that direction, indicating a high magnetocrystalline anisotropy. The c axis is of intermediate hardness. The magnetic properties of this material are therefore very different from those of the related Gd 5 Si 2 Ge 2 system, in which the b axis was found to be the easy axis and the magnitude of the anisotropy was smaller. The Tb 5 ͑Si x Ge 4−x ͒ alloy system has many features in common with the Gd 5 ͑Si x Ge 4−x ͒ system although it has a more complex magnetic and structural phase diagram. This paper reports on the magnetic anisotropy and magnetic phase transition of single-crystal Tb 5 ͑Si 2.2 Ge 1.8 ͒ which has been investigated by the measurements of M-H and M-T along the a, b, and c axes. The variation of 1 / vs T indicates that there is a transition from paramagnetic to ferromagnetic at T c = 110 K. Below this transition temperature M-H curves show very strong anisotropy, and it is believed that this is due to the complex spin configuration. M-H measurements at T = 110 K show that the a axis is the easy axis, and that the saturation magnetization is 200 emu/ g. The b axis is the hard axis, which needs an external magnetic field much higher than 2 T to saturate the magnetization in that direction, indicating a high magnetocrystalline anisotropy. The c axis is of intermediate hardness. The magnetic properties of this material are therefore very different from those of the related Gd 5 Si 2 Ge 2 system, in which the b axis was found to be the easy axis and the magnitude of the anisotropy was smaller. Keywords

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Magnetic anisotropy and phase transitions in single-crystal Tb5(Si2.2Ge1.8)

Han

Snyder

Tang

et al. 2005

Journal of Applied Physics

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“…The field-induced, reversible nature of the magnetostructural transition then results in strong magnetostriction 14 and giant ͑negative͒ magnetoresistance. 16 For xр0.2, a second-order PM-toantiferromagnetic ͑AFM͒ transition occurs at T N ͑from ϳ125 K for xϭ0 to ϳ135 K for xϭ0.2). 6 Upon further cooling, a first-order AFM-FM transition takes place, whose temperature ranges linearly from about 20 K (xϭ0) to 120 K (xϭ0.2).…”

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confidence: 99%

Scaling of the entropy change at the magnetoelastic transition inGd5(SixGe

et al. 2002

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Differential scanning calorimetry under a magnetic field H has been used to measure the entropy change ⌬S at the magnetoelastic transition in Gd 5 (Si x Ge 1Ϫx ) 4 alloys, for xр0.5. We show that ⌬S scales with the transition temperature, T t , which is tuned by x and H, from 70 to 310 K. Such a scaling demonstrates that T t is the relevant parameter in determining the giant magnetocaloric effect in these alloys, and proves that the magnetovolume effects due to H are of the same nature as the volume effects caused by substitution. DOI: 10.1103/PhysRevB.66.212402 PACS number͑s͒: 75.30.Sg, 75.20.En, 75.40.Cx, 75.50.Cc The magnetocaloric effect ͑MCE͒ has been studied for decades owing to its potential application to magnetic refrigerants. 1 The MCE is the isothermal entropy change or the adiabatic temperature change arising from the application or removal of a magnetic field H on a system with magnetic degrees of freedom. Many efforts have been devoted to the analysis of the MCE both in the vicinity of second-order magnetic phase transitions, where Gd is the element that shows the largest effect close to room temperature, 1,2 and in order-disorder blocking processes, e.g., in molecular magnets. 3 However, the MCE may be maximized in the vicinity of a first-order magnetoelastic phase transition, when the crystallographic transformation is field induced, resulting in an additional contribution to the entropy change 4,1 : a giant MCE has been discovered in the Gd 5 (Si x Ge 1Ϫx ) 4 compounds with xр0.5, [5][6][7] and recently in MnAs-based materials. 8,9 This paper is aimed at studying the entropy change ⌬S associated with the first-order magnetoelastic phase transition in Gd 5 (Si x Ge 1Ϫx ) 4 alloys, which has lately aroused much discussion. 5,10-13 Two compositional ranges are of interest. For 0.24рxр0.5, the giant MCE is related to a firstorder magnetoelastic phase transition from a hightemperature paramagnetic ͑PM͒, monoclinic phase ( P112 1 /a) to a low-temperature ferromagnetic ͑FM͒, Gd 5 Si 4 -type orthorombic-I phase ( Pnma), at temperatures ranging from 130 K (xϭ0.24) to 276 K (xϭ0.5). 6,14 The structural transition occurs by a shear mechanism 15 and yields a large volume contraction. The field-induced, reversible nature of the magnetostructural transition then results in strong magnetostriction 14 and giant ͑negative͒ magnetoresistance. 16 For xр0.2, a second-order PM-toantiferromagnetic ͑AFM͒ transition occurs at T N ͑from ϳ125 K for xϭ0 to ϳ135 K for xϭ0.2). 6 Upon further cooling, a first-order AFM-FM transition takes place, whose temperature ranges linearly from about 20 K (xϭ0) to 120 K (xϭ0.2). MCE is related to such a first-order phase transition. The nature of the AFM phase is currently under discussion, 17 and the magnetic structure may correspond to that of either a canted ferrimagnet, as proposed for Nd 5 Ge 4 ͑Ref. 18͒ or a canted antiferromagnet, as for the Ge-rich region of the Tb 5 (Si x Ge 1Ϫx ) 4 alloys. 19,20 The AFM-FM transition occurs simultaneously with a first-order structural tra...

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“…This is because of their interesting physical properties, such as the giant magnetocaloric effect, 1-4 colossal magnetostriction, [5][6][7][8] giant magnetoresistance, [9][10][11][12][13][14][15][16] and spontaneous generation of voltage ͑SGV͒, 17 that have been observed during the firstorder magnetostructural, ferromagnetic-orthorhombic to paramagnetic-monoclinic ͑on heating͒, phase transformation ͑see Refs. 5,18͒.…”

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confidence: 99%

Spontaneous generation of voltage in single-crystal Gd5Si2Ge2 during magnetostructural phase transformations

Zou

Tang

Schlagel

et al. 2006

Journal of Applied Physics

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The spontaneous generation of voltage ͑SGV͒ in single-crystal and polycrystalline Gd 5 Si 2 Ge 2 during the coupled magnetostructural transformation has been examined. Our experiments show reversible, measurable, and repeatable SGV responses of the materials to the temperature and magnetic field. The parameters of the response and the magnitude of the signal are anisotropic and rate dependent. The magnitude of the SGV signal and the critical temperatures and critical magnetic fields at which the SGV occurs vary with the rate of temperature and magnetic-field changes. Since their rediscovery in 1997, 1,2 the R 5 ͑Si x Ge 1−x ͒ 4 intermetallic compounds, where R is a lanthanide metal, continue to attract considerable attention. This is because of their interesting physical properties, such as the giant magnetocaloric effect, 1-4 colossal magnetostriction, 5-8 giant magnetoresistance, 9-16 and spontaneous generation of voltage ͑SGV͒, 17 that have been observed during the firstorder magnetostructural, ferromagnetic-orthorhombic to paramagnetic-monoclinic ͑on heating͒, phase transformation ͑see Refs. 5,18͒. Among them, the SGV is especially intriguing because it may result in the development of sensors, which can respond not only to changes in temperature, pressure, and/or magnetic field but most importantly to the rates of their changes without the need for a complicated analysis of signals. Furthermore, all of this can be done by a single sensor requiring no standby power.The SGV in the R 5 ͑Si x Ge 1−x ͒ 4 system was reported by Levin et al. in several polycrystalline samples of Gd 5 ͑Si x Ge 1−x ͒ 4 . 17 Because a current was not supplied, the voltages observed across the samples were regarded as spontaneous. The SGV occurs near first-order magnetostructural phase transformations. Here we report on the SGV during the first-order phase transition in several single-crystal Gd 5 Si 2 Ge 2 samples. In addition to the SGV behavior as a function of temperature and magnetic field, we also examine the anisotropy of the signal and its dependence on the variable rates of change of these stimuli.The Gd 5 Si 2 Ge 2 single crystal was prepared using the Bridgman method. 19 Three parallelepiped-shaped samples were cut from a large grain by electric discharge machining. The longest side of each sample was parallel to one of the three major crystallographic directions ͓100͔, ͓010͔, or ͓001͔, and specimen dimensions were 3.66ϫ 1.82ϫ 0.49, 4.06 ϫ 1.03ϫ 1.00, and 5.6ϫ 2.0ϫ 0.92 mm 3 , respectively. The SGV behaviors of a polycrystalline Gd 5 Si 2 Ge 2 sample with the dimensions of 6.57ϫ 2.48ϫ 1.85 mm 3 were also measured in order to verify previous observations 17 and to compare them with the single-crystal samples.The dc voltages across the samples were measured by a standard two-probe method and recorded as functions of time by a Keithley 181 nanovoltmeter. Readouts from the nanovoltmeter were computer recorded every 0.25 s. The temperature and magnetic-field changes exerted on the samples were regulated by a LakeShore Model 7225...

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Giant magnetoresistance near the magnetostructural transition in Gd5(Si1.8Ge2.2)

Cited by 190 publications

References 23 publications

Magnetic anisotropy and phase transitions in single-crystal Tb5(Si2.2Ge1.8)

Magnetic anisotropy and phase transitions in single-crystal Tb5(Si2.2Ge1.8)

Scaling of the entropy change at the magnetoelastic transition inGd5(SixGe

Spontaneous generation of voltage in single-crystal Gd5Si2Ge2 during magnetostructural phase transformations

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