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Register a new userEnhancement of positive magnetoresistance following a magnetic-field-induced ferromagnetic transition in an intermetallic compound, Tb5Si3
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Added by
E. V. Sampathkumaran
Publication date
2009
fields
Physics
and research's language is
English
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We report the existence of a field-induced ferromagnetic transition in the magnetically ordered state (<69 K) of an intermetallic compound, Tb5Si3, and this transition is distinctly first-order at 1.8 K (near 60 kOe), whereas it appears to become second order near 20 K. The finding we stress is that the electrical resistivity becomes suddenly large in the high-field state after this transition and this is observed in the entire temperature range in the magnetically ordered state. Such an enhancement of positive magnetoresistance (below 100 kOe) at the metamagnetic transition field is unexpected on the basis that the application of magnetic field should favor a low-resistive state due to alignment of spins.
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We report here the magneto-transport properties of the newly synthesized Heusler compound Cr2NiGa which crystallizes in a disordered cubic B2 structure belonging to Pm-3m space group. The sample is found to be paramagnetic down to 2 K with metallic character. On application of magnetic field, a significantly large increase in resistivity is observed which corresponds to magnetoresistance as high as 112% at 150 kOe of field at the lowest temperature. Most remarkably, the sample shows negative temperature coefficient of resistivity below about 50 K under the application of field gretare than or equal to 80 kOe, signifying a field-induced metal to `insulating transition. The observed magnetoresistance follows Kohlers rule below 20 K indicating the validity of the semiclassical model of electronic transport in metal with a single relaxation time. A multi-band model for electronic transport, originally proposed for semimetals, is found to be appropriate to describe the magneto-transport behavior of the sample.
The compound, Tb5Si3, crystallizing in Mn5Si3-type hexagonal structure, was recently reported by us to exhibit a sudden and huge enhancement in electrical resistivity (rho) at a critical magnetic field (H_cr) in the magnetically ordered state (<70 K) tracking isothermal magnetization (M) behavior. We have investigated the influence of external pressure (<15 kbar) and negative chemical pressure induced by Ge substitution for Si on M and rho as a function of temperature (5-300 K) and magnetic field (<120 kOe), with the primary aim of understanding the field-induced anomalies. Focussing on isothermal M and magnetoresistance (MR) at two temperatures, 5 and 20K, we find that this rho anomaly persists under external as well as negative chemical pressures, however with a large change in the H_cr. The pressure-derivative of H_cr is negative and this trend and the MR behavior at the H_cr are comparable to that observed in some Laves phase itinerant magnetic systems. On the basis of this observation, we speculate that the magnetic fluctuations induced at this critical field could be responsible for the MR anomal.ies
In this work we report the physical properties of the new intermetallic compound TbRhIn5 investigated by means of temperature dependent magnetic susceptibility, electrical resistivity, heat-capacity and resonant x-ray magnetic diffraction experiments. TbRhIn5 is an intermetallic compound that orders antiferromagnetically at TN = 45.5 K, the highest ordering temperature among the existing RRhIn5 (1-1-5, R = rare earth) materials. This result is in contrast to what is expected from a de Gennes scaling along the RRhIn5 series. The X-ray resonant diffraction data below TN reveal a commensurate antiferromagnetic (AFM) structure with a propagation vector (1/2 0 1/2) and the Tb moments oriented along the c-axis. Strong (over two order of magnitude) dipolar enhancements of the magnetic Bragg peaks were observed at both Tb absorption edges LII and LIII, indicating a fairly high polarization of the Tb 5d levels. Using a mean field model including an isotropic first-neighbors exchange interaction J(R-R) and the tetragonal crystalline electrical field (CEF), we were able to fit our experimental data and to explain the direction of the ordered Tb-moments and the enhanced TN of this compound. The evolution of the magnetic properties along the RRhIn5 series and its relation to CEF effects for a given rare-earth is discussed.
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Cubic spinel GeNi2O4 exhibits intriguing magnetic properties with two successive antiferromagnetic phase transitions (TN1 12.1 and TN2 11.4 K) with the absence of any structural transition. We have performed detailed heat capacity and magnetic measurements in different crystallographic orientations. A new magnetic phase in presence of magnetic field (H > 4 T) along the [111] direction is revealed, which is not observed when the magnetic field is applied along the [100] and [110] directions. High field neutron powder diffraction measurements confirm such a change in magnetic phase, which could be ascribed to a spin reorientation in the presence of magnetic field. A strong magnetic anisotropy and competing magnetic interactions play a crucial role on the complex magnetic behavior in this cubic system.
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