arXiv subjects

Kartik K Iyer

Publications and source records attributed to Kartik K Iyer.

45 records · Page 3Linked to original sources

arXiv2009

Magnetic anomalies in Gd6Co1.67Si3 and Tb6Co1.67Si3

The compounds, Gd6Co1.67Si3 and Tb6Co1.67Si3, recently reported to form in a Ce6Ni2Si3-derived hexagonal structure (space group: P6_3 / m) and to order magnetically below 295 and 190 K respectively, have been investigated by detailed magnetization (M) studies in the temperature interval 1.8-330 K as a function of magnetic field (H). The points of emphasis are: We observe multiple steps in the M(H) curve for the Tb compound at 1.8 K while increasing H, but these steps do not appear in the reverse cycle of H. At higher temperatures, such steps are absent. However, this 'staircase' behavior of M(H) is not observed for the Gd compound at any temperature and the isothermal magnetization is not hysteretic unlike in Tb compound. From the M(H) data measured at close intervals of temperature, we have derived isothermal entropy change (Delta S) and it is found that Delta S follows a theoretically predicted H^2/3-dependence.

cond-mat.str-el↗

arXiv2008

Stability of geometrically frustrated magnetic state of Ca3CoRhO6 to applications of positive and negative pressure

The influence of negative chemical pressure induced by gradual replacement of Ca by Sr as well as of external pressure (up to 10 kbar) on the magnetism of Ca3CoRhO6 has been investigated by magnetization studies. It is found that the solid solution, Ca(3-x)Sr(x)CoRhO6, exists at least till about x= 1.0 without any change in the crystal structure. Apart from insensitivity of the spin-chain feature to volume expansion, the characteristic features of geometrical frustration interestingly appear at the same temperatures for all compositions, in sharp contrast to the response to Y substitution for Ca (reported previously). Interestingly, huge frequency dependence of ac susceptibility known for the parent compound persists for all compositions. We do not find a change in the properties under external pressure. The stability of the magnetic anomalies of this compound to the volume change (about 4%) is puzzling.

cond-mat.str-el↗

arXiv2008

Large magnetocaloric effect in Gd4Co3

We report a large entropy change (DeltaS) below 300 K, peaking near TC= 220 K, due to isothermal change of magnetic field, for Gd4Co3, with a refrigeration capacity higher than that of Gd. Notably, the isothermal magnetization is nonhysteretic - an important criterion for magnetic refrigeration without loss. DeltaS behavior is also compared with that of magnetoresistance.

cond-mat.str-el↗

arXiv2008

The behavior of magnetic ordering and the KOndo effect in the alloys, Ce2Rh(1-x)Co(x)Si3: Evidence from bulk studies for Fermi-surface change during magnetic ordering - QCP transformation and applicability of SDW pictur

The results of magnetic susceptibility, electrical resistivity (rho), and heat capacity measurements as a function of temperature are reported for the alloys, Ce2Rh(1-x)Co(x)Si3, crystallizing in an AlB2-derived hexagonal strcture. Ce2RhSi3 exhibits antiferromagnetic ordering at 7 K. The Neel temperature decreases gradually with the increase in Co concentration. For x greater than 0.6, no magnetic ordering is observed down to 0.5 K. Interestingly, the x= 0.6 alloy exhibits signatutes of non-Fermi liquid behavior, while the Co end member is a Fermi liquid. Thus, a transformation of magnetic ordering state to non-magnetism via non-Fermiliquid state by isoelectronic chemical doping is evident in this solid solution. The electrical resistivity data for x= 0.2 and 0.3 alloys show an upturn at respective Neel temperatures, establishing the formation of a magnetism-induced pseudo-gap for these intermediate compositions alone as though there is a gradual Fermi surface transformation as the quantum critical point is approached.

cond-mat.str-el↗

arXiv2007

Magnetic anomalies in single crystalline ErPd2Si2

Considering certain interesting features in the previously reported 166Er Moessbauer effect and neutron diffraction data on the polycrystalline form of ErPd2Si2 crystallizing in ThCr2Si2-type tetragonal structure, we have carried out magnetic measurements (1.8 to 300 K) on the single crystalline form of this compound. We observe significant anisotropy in the absolute values of magnetization (indicating that the easy axis is c-axis) as well as in the features due to magnetic ordering in the plot of magnetic susceptibility (chi) versus temperature (T) at low temperatures. The chi(T) data reveal that there is a pseudo-low dimensional magnetic order setting in at 4.8 K, with a three-dimensional antiferromagnetic ordering setting in at a lower temperature (3.8 K). A new finding in the chi(T) data is that, for H//<110>, but not for H//<001>, there is a broad shoulder in the range 8-20 K, indicative of the existence of magnetic correlations above 5 K as well, which could be related to the previously reported slow-relaxation-dominated Moessbauer spectra. Interestingly, the temperature coefficient of electrical resistivity is found to be isotropic; no feature due to magnetic ordering could be detected in the electrical resistivity data at low temperatures, which is attributed to magnetic Brillioun-zone boundary gap effects. The results reveal complex nature of the magnetism of this compound.

cond-mat.str-el↗

arXiv2007

Geometrically frustrated magnetic behavior of Sr3NiRhO6 and Sr3NiPtO6

The results of ac and dc magnetic susceptibility isothermal magnetization and heat-capacity measurements as a function of temperature (T) are reported for Sr3NiRhO6 and Sr3NiPtO6 containing magnetic chains arranged in a triangular fashion in the basal plane and crystallizing in K4CdCl6-derived rhombohedral structure. The results establish that both the compounds are magnetically frustrated, however in different ways. In the case of the Rh compound, the susceptibility data reveal that there are two magnetic transitions, one in the range 10 -15 K and the other appearing as a smooth crossover near 45 K, with a large frequency dependence of ac susceptibility in the range 10 to 40 K; in addition, the features in C(T) are smeared out at these temperatures. The magnetic properties are comparable to those of previously known few compounds with partially disordered antiferromagnetic structure. On the other hand, for Sr3NiPtO6, there is no evidence for long-range magnetic ordering down to 1.8 K despite large value of paramagnetic Curie temperature.

cond-mat.str-el↗

arXiv2007

Superconducting behavior of the solid solution, Y2Pd(1-x)Pt(x)Ge3

The compound Y2PdGe3 was earlier reported by us to be one of the very few ternary superconducting compounds (T_c= 3 K) belonging to the same structure as that of MgB2. Here we report the results of electrical resistivity, magnetization and heat capacity measurements at low temperatures on the solid solution with a nominal starting composition, Y2Pd(1-x)Pt(x)Ge3, to understand the influence of gradual replacement of Pd by Pt on T_c. The superconducting properties of this solution is distinctly interesting in the sense that the Tc varies monotonically with increasing x in sharp contrast to the non-monotonic variation for other isostructural solid solutions reported recently.

cond-mat.supr-con↗

arXiv2007

Magnetic anomalies in a spin-chain compound, Sr3CuRhO6: Griffiths-phase-like behavior of magnetic susceptibility

We report the results of ac and dc magnetic susceptibility (chi), heat-capacity (C), isothermal magnetization and isothermal remanent magnetization measurements on the compound, Sr3CuRhO6, crystallizing in a K4CdCl6-derived monoclinic structure. The magnetization data reveal distinct magnetic anomalies near 6 and 12 K with decreasing temperature (T). While the transition below (To=) 6K appears to be of a spin-glass-type as inferred from all the data, the one at 12 K is not typical of bulk ferromagnetism in contrast to an earlier proposal. In the range 6 to 12 K, the dc chi obeys the theoretically expected form for very low dc fields and the values of chi decrease gradually with the application of higher magnetic fields, mimicking the behavior Griffiths-phases.

cond-mat.str-el↗

arXiv2006

Magnetic and magnetoresistance behavior of Tb7Rh3, an intermetallic compound with a negative temperature coefficient of electrical resistivity in the paramagnetic state, and Paramagnetic Giant Magnetoresistance Phenomenon

The results of dc magnetization, electrical and magnetoresistance and heat capacity measurements (2-300 K) on Tb7Rh3, crystallizing in Th7Fe3-type hexagonal structure, are reported. In this compound, magnetic ordering sets in around 90 K with additional transitions at low temperatures and the temperature coefficient of resistivity (R), dR/dT, is negative over a wide temperature range in the paramagnetic state. The present magnetization results reveal that this compound is apparently characterized by rich features in the magnetic-field-temperature phase diagram. A point of major emphasis is that the sign of dR/dT in the paramagnetic state can be gradually changed by the application of magnetic field. As a result, the magnitude of the magnetoresistance (MR) is rather large even in the vicinity of room temperature (far above magnetic ordering temperature), in addition to giant MR behavior in the magnetically ordered state. Viewed together With similar behavior for other heavy rare-earth members of this series, this class of compounds can be classified as Paramagnetic Giant Magnetoresistance Systems. A new theoretical approach is warranted to understand this phenomenon.

cond-mat.str-el↗