Abstract:We report the results of various measurements, namely magnetization, complex dielectric permittivity and electric polarization (P) on Dy 2 BaNiO 5 as a function of temperature (T) and magnetic-field (H), apart from heat-capacity (C), with the primary motivation of exploring the existence of magnetoelectric (ME) coupling among Haldane spin-chain systems. The M(T) and C(T) data establish long range magnetic ordering at 58K. The most noteworthy observations are:

We bring out novel dielectric behavior of a spin-chain compound, Ca 3 Co 2 O 6 , undergoing Néel order at (T N 5) 24 K. It is found that the virgin curve in the plot of isothermal dielectric constant (e') versus magnetic-field lies outside the 'butterfly-shaped' envelope curve well below T N (e.g., 2.6 K), with a signature of a partial arrest of the high-field magnetoelectric (ME) phase in zero-field after travelling through magnetic-field-induced magnetic transitions. This behavior is in contrast to that observed in the isothermal magnetization data. Thus, this work brings out a novel case for 'phase-coexistence phenomenon' due to ME coupling. Another strange finding is that there is a weak, but a broad, peak in e' around 85-115 K well above T N , attributable to incipient spin-chain magnetic ordering. This finding should inspire further work to study ME coupling on artificial assemblies of magnetic chains, also keeping in mind miniaturization required for possible applications.T he search for materials with multiferroicity (for instance, those in which magnetic ordering and ferrolectricity are coupled) and with strong magnetolectric (ME) coupling has picked up momentum in recent years 1,2 due to application potential of such materials as well as from the fundamental science angle. As a result of such a coupling between seemingly different phenomena, these two phases can intriguingly coexist under favorable circumstances 3 , bearing relevance to the currently active topic of 'phase-coexistence phenomenon' in general in solids 4 . It is therefore of great interest to search for novel aspects of such a phase-coexistence situations arising out of this cross-coupling -an area which is yet to pick-up momentum. Another area remaining largely unexplored theoretically as well as experimentally is the investigation of ME coupling in magnetically isolated spin-chains, though this question was previously addressed in an organic one-dimensional quantum magnet and spin-Peierls instability was proposed to play a role on ME coupling 5 . Therefore, in order to enable magnetically controllable electric effects, for miniaturization of devices for applications commonly in particular, it is important to investigate whether the ME coupling within spin-chains (in the paramagnetic state) is in general more widespread without any restriction on spin values. Here, we demonstrate experimentally that the naturally occurring spin-chain oxide, Ca 3 Co 2 O 6 6 , with spin 5 2 on Co, turns out to be a novel material with 'exotic' dielectric properties, providing an ideal playground to probe both these aspects. We carried out complex dielectric measurements for this compound as a function of temperature (T) and magnetic-field (H). We find distinct intriguing features attributable to (i) a novel magnetoelectric phase-coexistence phenomenon following a magnetic-field-induced transition in the magnetically ordered state, and (ii) magnetoelectric coupling effect from spin-chains well above long range magnetic ordering.The Co spin-chains are place...

The results of magnetic susceptibility, electrical resistivity ͑͒, and heat-capacity measurements as a function of temperature are reported for the alloys, Ce 2 Rh 1−x Co x Si 3 , crystallizing in an AlB 2 -derived hexagonal structure. Ce 2 RhSi 3 exhibits antiferromagnetic ordering at 7 K. The Néel temperature decreases gradually with the increase in Co concentration. For x ജ 0.6, no magnetic ordering is observed down to 0.5 K. Interestingly, the x = 0.6 alloy exhibits signatures of non-Fermi-liquid behavior, while the Co end member is a Fermi liquid. Thus, a transformation of magnetic-ordering state to nonmagnetism via non-Fermi-liquid state by isoelectronic chemical doping is evident in this solid solution. The heat-capacity data reveal a dominant role of Kondo compensation in the magnetically ordered state. The electrical resistivity data for x = 0.2 and 0.3 alloys show an upturn at respective Néel temperatures, establishing the formation of a magnetism-induced pseudogap for these intermediate compositions alone as though there is a gradual Fermi surface transformation as the quantum critical point is approached.

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We report an unusual temperature (T) dependent electrical resistivity (rho) behavior in a class of ternary intermetallic compounds of the type RCuAs2 (R=rare earths). For some rare earths (Sm, Gd, Tb, and Dy) with negligible 4f hybridization, there is a pronounced minimum in rho(T) far above respective Néel temperatures (T(N)). However, for the rare earths which are more prone to exhibit such a rho(T) minimum due to 4f-covalent mixing and the Kondo effect, this minimum is depressed. These findings, difficult to explain within the hitherto-known concepts, present an interesting scenario in magnetism.