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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

Temperature variations of resistivity and MR effect.(a) Resistivity measurements with current I along the a and c axes under applied magnetic fields of 0, 1 and 8 T. T1 = 100 K labels the temperature where one structural anomaly occurs as shown in Fig. 1 . The dashed lines are fits between 10 K and 40 K (details in text), and extrapolated to higher temperatures. (b) Corresponding MR values versus temperature. The MR effect along the a axis has a similar trend to that of the c axis albeit with a lower value. The positive MR values decrease sharply with increasing temperature below ~20 K, then gradually transfer into negative around TN, and persist up to ~120 K. By contrast, in amorphous GdxSi1–x films, only the NMRV was observed161718 near the metal-insulator transition. In (a), there is no big difference for the data at 0 and 1 T above ~20 K. The solid lines in (a) and (b) in the dashed arrow direction in turn correspond to the ordinal axis-direction and applied magnetic-field strength as labeled, respectively.
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f2: Temperature variations of resistivity and MR effect.(a) Resistivity measurements with current I along the a and c axes under applied magnetic fields of 0, 1 and 8 T. T1 = 100 K labels the temperature where one structural anomaly occurs as shown in Fig. 1 . The dashed lines are fits between 10 K and 40 K (details in text), and extrapolated to higher temperatures. (b) Corresponding MR values versus temperature. The MR effect along the a axis has a similar trend to that of the c axis albeit with a lower value. The positive MR values decrease sharply with increasing temperature below ~20 K, then gradually transfer into negative around TN, and persist up to ~120 K. By contrast, in amorphous GdxSi1–x films, only the NMRV was observed161718 near the metal-insulator transition. In (a), there is no big difference for the data at 0 and 1 T above ~20 K. The solid lines in (a) and (b) in the dashed arrow direction in turn correspond to the ordinal axis-direction and applied magnetic-field strength as labeled, respectively.

Mentions: The CEF is mainly responsible for the giant MS effect in rare-earth (RE) compounds. This effect is thus expected to be negligible in GdSi. However, below T1, structural parameters shown in Fig. 1a obviously deviate from the theoretical estimates (solid lines) by the Grüneisen (Gr) law, e.g., , and , denoting large anisotropic spontaneous MS effects. The formation of long-range-ordered (LRO) AFM state is a process of the growth of sublattice FM domains. The enlargement of FM domain volumes with decreasing temperature may accumulate strains on the domain walls, which is the microscopic mechanism for the magnetic-field-induced MS effect in ferromagnets. Therefore, including the effect of the molecular field of one Gd-AFM-sublattice on the other is indispensable to understand the spontaneous MS effect in GdSi. According to the Stoner model for itinerant magnetic electrons, the positive magnetic pressure PM associated with the magnetic ordering in a band is proportional to , where D, V and M represent the electronic density of states at the Fermi energy, the volume and the magnetic moment, respectively. The spontaneous PMV effect (i.e., NTVE), e.g., , is therefore attributed mainly to the increases of D (corresponding to the pronounced decrease of ρ below TN in Fig. 2a) and the induced itinerate spin-moments in conduction bands. Similar MS and MV effects were also reported in Gd3Ni15, where, however, they are ascribed to the itinerant character of the Ni 3d bands.


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)

Temperature variations of resistivity and MR effect.(a) Resistivity measurements with current I along the a and c axes under applied magnetic fields of 0, 1 and 8 T. T1 = 100 K labels the temperature where one structural anomaly occurs as shown in Fig. 1 . The dashed lines are fits between 10 K and 40 K (details in text), and extrapolated to higher temperatures. (b) Corresponding MR values versus temperature. The MR effect along the a axis has a similar trend to that of the c axis albeit with a lower value. The positive MR values decrease sharply with increasing temperature below ~20 K, then gradually transfer into negative around TN, and persist up to ~120 K. By contrast, in amorphous GdxSi1–x films, only the NMRV was observed161718 near the metal-insulator transition. In (a), there is no big difference for the data at 0 and 1 T above ~20 K. The solid lines in (a) and (b) in the dashed arrow direction in turn correspond to the ordinal axis-direction and applied magnetic-field strength as labeled, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Temperature variations of resistivity and MR effect.(a) Resistivity measurements with current I along the a and c axes under applied magnetic fields of 0, 1 and 8 T. T1 = 100 K labels the temperature where one structural anomaly occurs as shown in Fig. 1 . The dashed lines are fits between 10 K and 40 K (details in text), and extrapolated to higher temperatures. (b) Corresponding MR values versus temperature. The MR effect along the a axis has a similar trend to that of the c axis albeit with a lower value. The positive MR values decrease sharply with increasing temperature below ~20 K, then gradually transfer into negative around TN, and persist up to ~120 K. By contrast, in amorphous GdxSi1–x films, only the NMRV was observed161718 near the metal-insulator transition. In (a), there is no big difference for the data at 0 and 1 T above ~20 K. The solid lines in (a) and (b) in the dashed arrow direction in turn correspond to the ordinal axis-direction and applied magnetic-field strength as labeled, respectively.
Mentions: The CEF is mainly responsible for the giant MS effect in rare-earth (RE) compounds. This effect is thus expected to be negligible in GdSi. However, below T1, structural parameters shown in Fig. 1a obviously deviate from the theoretical estimates (solid lines) by the Grüneisen (Gr) law, e.g., , and , denoting large anisotropic spontaneous MS effects. The formation of long-range-ordered (LRO) AFM state is a process of the growth of sublattice FM domains. The enlargement of FM domain volumes with decreasing temperature may accumulate strains on the domain walls, which is the microscopic mechanism for the magnetic-field-induced MS effect in ferromagnets. Therefore, including the effect of the molecular field of one Gd-AFM-sublattice on the other is indispensable to understand the spontaneous MS effect in GdSi. According to the Stoner model for itinerant magnetic electrons, the positive magnetic pressure PM associated with the magnetic ordering in a band is proportional to , where D, V and M represent the electronic density of states at the Fermi energy, the volume and the magnetic moment, respectively. The spontaneous PMV effect (i.e., NTVE), e.g., , is therefore attributed mainly to the increases of D (corresponding to the pronounced decrease of ρ below TN in Fig. 2a) and the induced itinerate spin-moments in conduction bands. Similar MS and MV effects were also reported in Gd3Ni15, where, however, they are ascribed to the itinerant character of the Ni 3d bands.

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