Novel dielectric anomalies due to spin-chains above and below Néel temperature in Ca3Co2O6

Abstract

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...

Multiglass properties and magnetoelectric coupling in the uniaxial anisotropic spin-cluster-glassFe2TiO5

“…The observed frequency dependence may reflect slow electric-dipole dynamics, which are yet to be unraveled. The frequency dependencies in both ac susceptibility and complex dielectric properties are scarce for stoichiometric (that is, undoped) compounds, barring a few exceptions [27,28]. The demonstrations of distinct memory effect both in magnetic and dielectric studies support multiglass behavior of FTO as was first time observed in the ME multiglass SrTi 0.98 Mn 0.02 O 3 [6].…”

Complex nature of magnetic field induced ferroelectricity in GdCrTiO5

“…This kind of unusual ME behaviour due to complex dynamics of spins and dipoles is rare in the literature; for example, a magnetodielectric phase-coexistence is observed in the spin-chain compound Ca 3 Co 2 O 6 without any fingerprints of such a phase-co-existence in isothermal magnetization measurements, despite strong intrinsic magnetodielectric coupling in this complex compound. 27 The results suggest that spin-induced ferroelectricity in RCrTiO 5 may be governed by DM interactions due to the Cr moments, significantly influenced by R-moments. It has to be noted that a finite magnetodielectric coupling (dielectric constant as a function of H, which consists higher order coupling term as well) for GdCrTiO 5 exists even for temperatures up to 20 K. 15 This fact could arise from magnetic exchange frustration resulting from competing exchange interactions between Gd and Cr moments, active even above magnetic ordering (> 10 K).…”

Magnetic and dielectric behavior of the spin-chain compound Er2BaNiO5 well below its Néel temperature

“…In the case of Dy member, it was noted that, in addition to the multiferroic behavior setting in at (T N =) 58 K, there is an additional transition at temperatures (T) well below T N , as though there is a 'reentrant phenomenon' into a complex multiglass-like state below 10 K. Such a phenomenon is not so commonly known particularly among undoped stoichiometric compounds in the field of multiferroics, barring a few examples (see, Ref. 5,7 and articles cited therein), though the concept of multi-glass was originally discussed in some doped materials [8]. It is therefore of interest to study low temperature properties of other members of this family well below their respective T N .…”