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Possible magnetic-polaron-switched positive and negative magnetoresistance in the GdSi single crystals.

Li H, Xiao Y, Schmitz B, Persson J, Schmidt W, Meuffels P, Roth G, Brückel T - Sci Rep (2012)

Bottom Line: Around T(N) the PMRV translates to negative, down to ~-10.5%.Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins.Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices.

View Article: PubMed Central - PubMed

Affiliation: Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at Institut Laue-Langevin, Boîte Postale 156, F-38042 Grenoble Cedex 9, France. h.li@fz-juelich.de

ABSTRACT
Magnetoresistance (MR) has attracted tremendous attention for possible technological applications. Understanding the role of magnetism in manipulating MR may in turn steer the searching for new applicable MR materials. Here we show that antiferromagnetic (AFM) GdSi metal displays an anisotropic positive MR value (PMRV), up to ~415%, accompanied by a large negative thermal volume expansion (NTVE). Around T(N) the PMRV translates to negative, down to ~-10.5%. Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins. Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices.

No MeSH data available.


Related in: MedlinePlus

Field- and temperature- dependent MR values.(a) Field and temperature dependencies of the MR values with I∥c-axis and applied magnetic field, μ0H, along the a or c axis below TN, and (b) above TN. The representatives of the linear-field dependence of the PMRV (i.e., the PMRV is proportional to the strength of applied magnetic field) at 7 K (blow TN) and the quadratic variation of the NMRV (i.e., the absolute NMRV is proportional to the square of the strength of applied magnetic field) at 60 K (above TN) were shown in (a) and (b), respectively. (c) Field and temperature dependencies of the MR values with I∥a-axis and applied magnetic field, μ0H, along the b or c axis below TN, and (d) above TN.
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f4: Field- and temperature- dependent MR values.(a) Field and temperature dependencies of the MR values with I∥c-axis and applied magnetic field, μ0H, along the a or c axis below TN, and (b) above TN. The representatives of the linear-field dependence of the PMRV (i.e., the PMRV is proportional to the strength of applied magnetic field) at 7 K (blow TN) and the quadratic variation of the NMRV (i.e., the absolute NMRV is proportional to the square of the strength of applied magnetic field) at 60 K (above TN) were shown in (a) and (b), respectively. (c) Field and temperature dependencies of the MR values with I∥a-axis and applied magnetic field, μ0H, along the b or c axis below TN, and (d) above TN.

Mentions: The most intriguing results from resistivity measurements are the anisotropic MR effect (Figs 2b, 3 and 4) and the existence of both positive and negative MR values, up to ~415% (comparable to the CMR value in manganites16 and one to two orders of magnitude larger than that of the RE-metals21) and down to ~−10.5% along the c axis at 8 T and 3 K and 52.8 K, respectively. The MR anisotropy in the ac and bc plans is shown in Fig. 3. They display a twofold symmetry at 7K (Figs 3a and 3d). We notice that applied magnetic field of 8 T does not suppress (produce) the (a) hump along the c and a axes, respectively, near TN, and the MR twofold symmetry is persistent from 1 to 8 T, indicating that applied magnetic field in a strength of 8 T may just align or localize the 5d moments, and slightly rotate and tilt the 4f moments while conserving the superzone energy gap. Therefore, the MR effect in GdSi exhibits a well separate feature of the temperature regions for the positive and the negative MR values (Fig. 2b), respectively, which is induced jointly by the AFM superzone effect19 and the shift of the AFM transition to lower temperatures in external applied magnetic field analogous to the case in manganites126. For metals, mean-field theories predict that spin fluctuations induced by applied magnetic field from the localized magnetism produce a PMRV with the quadratic-field dependence in antiferromagnets, whereas a NMRV with the linear variation in ferromagnets and paramagnets22. However, in GdSi, the PMRV in the AFM state mainly displays a linear magnetic-field dependence (Figs 4a and 4c), while above TN1 the absolute NMRV is proportional to the square of the strength of applied magnetic field (Figs 4b and 4d). Both the positive and negative MR effects do not saturate at utilized maximum μ0H = 8 T (Fig. 4). In addition, the ratio of the resistivity at 160 K and 7 K in Fig. 2a is already ~12–25, therefore, the cyclotron motion of the conduction electrons could be neglected at μ0H = 8 T (i.e., , where ωc is the cyclotron frequency and τ is the life time of the conduction electrons). Therefore, these uncommon magnetic-field variations indicate new transport mechanisms for the MR effects of GdSi.


Possible magnetic-polaron-switched positive and negative magnetoresistance in the GdSi single crystals.

Li H, Xiao Y, Schmitz B, Persson J, Schmidt W, Meuffels P, Roth G, Brückel T - Sci Rep (2012)

Field- and temperature- dependent MR values.(a) Field and temperature dependencies of the MR values with I∥c-axis and applied magnetic field, μ0H, along the a or c axis below TN, and (b) above TN. The representatives of the linear-field dependence of the PMRV (i.e., the PMRV is proportional to the strength of applied magnetic field) at 7 K (blow TN) and the quadratic variation of the NMRV (i.e., the absolute NMRV is proportional to the square of the strength of applied magnetic field) at 60 K (above TN) were shown in (a) and (b), respectively. (c) Field and temperature dependencies of the MR values with I∥a-axis and applied magnetic field, μ0H, along the b or c axis below TN, and (d) above TN.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3475993&req=5

f4: Field- and temperature- dependent MR values.(a) Field and temperature dependencies of the MR values with I∥c-axis and applied magnetic field, μ0H, along the a or c axis below TN, and (b) above TN. The representatives of the linear-field dependence of the PMRV (i.e., the PMRV is proportional to the strength of applied magnetic field) at 7 K (blow TN) and the quadratic variation of the NMRV (i.e., the absolute NMRV is proportional to the square of the strength of applied magnetic field) at 60 K (above TN) were shown in (a) and (b), respectively. (c) Field and temperature dependencies of the MR values with I∥a-axis and applied magnetic field, μ0H, along the b or c axis below TN, and (d) above TN.
Mentions: The most intriguing results from resistivity measurements are the anisotropic MR effect (Figs 2b, 3 and 4) and the existence of both positive and negative MR values, up to ~415% (comparable to the CMR value in manganites16 and one to two orders of magnitude larger than that of the RE-metals21) and down to ~−10.5% along the c axis at 8 T and 3 K and 52.8 K, respectively. The MR anisotropy in the ac and bc plans is shown in Fig. 3. They display a twofold symmetry at 7K (Figs 3a and 3d). We notice that applied magnetic field of 8 T does not suppress (produce) the (a) hump along the c and a axes, respectively, near TN, and the MR twofold symmetry is persistent from 1 to 8 T, indicating that applied magnetic field in a strength of 8 T may just align or localize the 5d moments, and slightly rotate and tilt the 4f moments while conserving the superzone energy gap. Therefore, the MR effect in GdSi exhibits a well separate feature of the temperature regions for the positive and the negative MR values (Fig. 2b), respectively, which is induced jointly by the AFM superzone effect19 and the shift of the AFM transition to lower temperatures in external applied magnetic field analogous to the case in manganites126. For metals, mean-field theories predict that spin fluctuations induced by applied magnetic field from the localized magnetism produce a PMRV with the quadratic-field dependence in antiferromagnets, whereas a NMRV with the linear variation in ferromagnets and paramagnets22. However, in GdSi, the PMRV in the AFM state mainly displays a linear magnetic-field dependence (Figs 4a and 4c), while above TN1 the absolute NMRV is proportional to the square of the strength of applied magnetic field (Figs 4b and 4d). Both the positive and negative MR effects do not saturate at utilized maximum μ0H = 8 T (Fig. 4). In addition, the ratio of the resistivity at 160 K and 7 K in Fig. 2a is already ~12–25, therefore, the cyclotron motion of the conduction electrons could be neglected at μ0H = 8 T (i.e., , where ωc is the cyclotron frequency and τ is the life time of the conduction electrons). Therefore, these uncommon magnetic-field variations indicate new transport mechanisms for the MR effects of GdSi.

Bottom Line: Around T(N) the PMRV translates to negative, down to ~-10.5%.Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins.Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices.

View Article: PubMed Central - PubMed

Affiliation: Jülich Centre for Neutron Science JCNS, Forschungszentrum Jülich GmbH, Outstation at Institut Laue-Langevin, Boîte Postale 156, F-38042 Grenoble Cedex 9, France. h.li@fz-juelich.de

ABSTRACT
Magnetoresistance (MR) has attracted tremendous attention for possible technological applications. Understanding the role of magnetism in manipulating MR may in turn steer the searching for new applicable MR materials. Here we show that antiferromagnetic (AFM) GdSi metal displays an anisotropic positive MR value (PMRV), up to ~415%, accompanied by a large negative thermal volume expansion (NTVE). Around T(N) the PMRV translates to negative, down to ~-10.5%. Their theory-breaking magnetic-field dependencies [PMRV: dominantly linear; negative MR value (NMRV): quadratic] and the unusual NTVE indicate that PMRV is induced by the formation of magnetic polarons in 5d bands, whereas NMRV is possibly due to abated electron-spin scattering resulting from magnetic-field-aligned local 4f spins. Our results may open up a new avenue of searching for giant MR materials by suppressing the AFM transition temperature, opposite the case in manganites, and provide a promising approach to novel magnetic and electric devices.

No MeSH data available.


Related in: MedlinePlus