Browsing by Author "Her, J. L."

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Anisotropy in the upper critical field of FeSe and FeSe0.33Te0.67 single crystals
(2015-04-01)
Her, J. L.
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Kohama, Y.
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Matsuda, Y. H.
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Kindo, K.
;
Yang, W-H
The electric resistivity of single crystalline Fe-based superconductors FeSe and FeSe0.33Te0.67 was measured in pulsed magnetic fields up to 55 T. Te-doped iron selenide, FeSe0.33Te0.67, shows rather isotropic behavior in both magnetoresistance (MR) and upper critical fields (H-c2(perpendicular to)(0)/H-c2(parallel to)(0) = 48 T/42 T similar to 1.14), when an external magnetic field is applied parallel and perpendicular to the crystallographic c-axis. These isotropic behaviors are frequently observed in an iron-based superconductor, and the isotropy in H-c2 can likely be described by the Pauli effect. In contrast, our measurements elucidate that the undoped iron selenide, FeSe, exhibits a clear anisotropy in both MR and H-c2 (H-c2(perpendicular to)(0)/H-c2(parallel to)(0) = 27 T/15 T similar to 1.8). This behavior occurs because the clean in-plane conduction (RRR = 35) allows to form a closed electron orbit within the two-dimensional Fermi sheets only for the magnetic field parallel to the c-axis, which results in an appearance of an intrinsic (orbital-effect limited) upper critical field for the undoped FeSe. Doping of Te breaks the clean in-plane conduction and leads to a crossover from an orbital limit dominating behavior to a Pauli limit dominating one.
Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr(2)S(4)
(2010-03-22)
Sun, C. P.
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Huang, C. L.
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Lin, C. C.
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Her, J. L.
;
Ho, C. J.
Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr(2)S(4) are reported. It is found that a metal-insulator transition in CdCr(2)S(4) is triggered by the electrical field. In magnetic fields, the resistivity rho of CdCr(2)S(4) responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr(2)S(4) the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.
Colossal electroresistance and colossal magnetoresistance in spinel multiferroic CdCr2S4
(2010-03-22)
Sun, C. P.
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Huang, C. L.
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Lin, C. C.
;
Her, J. L.
;
Ho, C. J.
Colossal magnetoresistance (CMR) and colossal electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity rho of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive, colossal electrocapacitive, CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.
Metamagnetic transitions and magnetoelectric coupling in acentric and nonpolar Pb2MnO4
(2019-05-16)
Kakarla, D. Chandrasekhar
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Wu, H. C.
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Hsieh, D. J.
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Sun, P. J.
;
Dai, G. J.
Acentric and nonpolar Pb2MnO4 was predicted to exhibit unique multipiezo induced magnetoelectric (ME) phenomena. In this paper, we present the results of magnetization as well as dielectric properties as a function of temperature (T), magnetic field (H), pressure (P), and electric field (E) primarily to address the ME coupling and identify the underlying mechanism behind this phenomenon. Magnetization and specific-heat measurements reveal the antiferromagnetic ordering of Mn4+ spins at temperature T-N= 17 K. Metamagnetic transitions at three critical magnetic fields H-c1, H-c2 and H-c3) are observed for T < T-N and H > 3.5 T. Further, the influences of pressure and magnetic field on H-c1 and H-c2 are investigated. The T-N, H-c1, and H(c2)( )all decrease with increasing external pressure. The dielectric anomaly observed at T-N is influenced by applying a magnetic field of H > 3.5 T. However, the electric field has minimal influence on the metamagnetic transition. The scaling between dielectric constant and magnetization meaningfully resolves the existence of magnetic-field-induced higher-order ME coupling in Pb2MnO4 at T < T-N and H > 3.5 T.
Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombic HoMnO(3) thin films
(2009-01-14)
Lin, T. H.
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Shih, H. C.
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Hsieh, C. C.
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Luo, C. W.
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Lin, J-Y
We investigated the magnetic and ferroelectric properties of c-axis oriented orthorhombic phase HoMnO(3) (o-HMO in Pbnm symmetry setting) thin films grown on Nb-doped SrTiO(3)(001) substrates. The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of the orientation of the applied field. However, an additional magnetic ordering occurring around 35 K was observed when the field was applied along the c-axis of o-HMO, which was absent when the field was applied in the ab-plane. The magnetocapacitance measured along the c-axis showed that although there is evidence of dielectric constant enhancement when the temperature is below 35 K the expected abrupt change in dielectric constant appears at a much lower temperature and reaches maximum around 13.5 K, indicating that the low-temperature c-axis polarization might be related to the ordering of the Ho(3+) moment. The lattice constant analyses using x-ray diffraction and the observation of a slight magnetization hysteresis suggest that the weak second magnetic transition along the c- axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.
Strain-induced effects on antiferromagnetic ordering and magnetocapacitance in orthorhombic HoMnO3 thin films
(2009-01-14)
Lin, T. H.
;
Shih, H. C.
;
Hsieh, C. C.
;
Luo, C. W.
;
Lin, J-Y
We investigated the magnetic and ferroelectric properties of c-axis oriented orthorhombic phase HoMnO3 (o-HMO in Pbnm symmetry setting) thin films grown on Nb-doped SrTiO3(001) substrates. The o-HMO films exhibit an antiferromagnetic ordering near 42 K, irrespective of the orientation of the applied field. However, an additional magnetic ordering occurring around 35 K was observed when the field was applied along the c-axis of o-HMO, which was absent when the field was applied in the ab-plane. The magnetocapacitance measured along the c-axis showed that although there is evidence of dielectric constant enhancement when the temperature is below 35 K the expected abrupt change in dielectric constant appears at a much lower temperature and reaches maximum around 13.5 K, indicating that the low-temperature c-axis polarization might be related to the ordering of the Ho3+ moment. The lattice constant analyses using x-ray diffraction and the observation of a slight magnetization hysteresis suggest that the weak second magnetic transition along the c- axis at 35 K might be more relevant to the strain-induced effect on antiferromagnetism.