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

Abstract

We have recently reported that the Haldane spin-chain system, Er 2 BaNiO 5 , undergoing antiferromagnetic order below (T N = ) 32 K, is characterized by the onset of ferroelectricity near 60K due to magnetoelectric coupling induced by short-range magnetic-order within spin-chains. We have carried out additional magnetic and dielectric studies to understand the properties well below T N . We emphasize here on the following: (i) A strong frequency dependent behaviors of ac magnetic susceptibility and complex dielectric properties have been observed at much lower temperatures (< 8 K), that is, 'reentrant multiglass-like' phenomenon, naturally suggesting the existence of an additional transition well below T N . ii) 'Magnetoelectric phase coexistence' is observed at very low temperature (e.g., T =2K), where the high-field magnetoelectric phase is partially arrested on returning to zero magnetic field after a cycling through metamagnetic transition.# Current address: UGC-DAE Consortium for Scientific Research, University Campus, Khandwa Road, Indore -452001, India 2 INTRODUCTIONThe Haldane [1] spin-chain systems of the type, R 2 BaNiO 5 (R= Rare-earths), have been paid a lot of attention for the past few decades from magnetism angle. Recently, some members of this family (R= Gd, Dy, Ho and Er) of oxides attracted further interest from the angle of magnetoelectric (ME) / magnetodielectric (MDE) coupling phenomenon [2][3][4][5][6]. A systematic study on the Er member [5] suggested that a displacive-type mechanism involving magnetic ions is responsible for the onset ferroelectricity well above its Néel temperature (T N = 32 K) and that short-range magnetic correlations are interestingly sufficient enough to induce the same. 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 . With this primary motivation, in this article, we report the results of our investigation on the Er member well below its T N . The results reveal that there are glassy anomalies both in magnetization and dielectric properties far below T N , characterizing that this compound also belongs to a new family of 'reentrant' multiferroic oxides. Additionally, there are features in the isothermal data attributable to 'magnetoelectric phase-co-existence' phenomenon.

Extraordinarily large intrinsic magnetodielectric coupling of the Tb member within the Haldane spin-chain family R2BaNiO5

“…The homogeneity of the sample was further confirmed by scanning electron microscope and the composition (within 2%) was confirmed by energydispersive x-ray analysis. Instruments used for measurements of magnetization, heat-capacity (C), and dielectric permittivity as a function of T down to 1.8 K and in magnetic-fields have been described in our earlier publications [7,[19][20][21][22][23]. Bias electric-field (E) measurements were done with the help of a Keithley 6517B electrometer.…”

“…Many members of this rare-earth family have been shown [7,[20][21][22][23] to reveal spin-glass characteristics at low temperatures (<10 K) well below respective TN. In order to confirm the absence of spin-glass freezing in this case, we performed isothermal remnant magnetization (MIRM) studies at 2, 5 and 20 K. That is, after cooling the specimen in zero-field to the desired temperature, a field of 5 kOe was switched on for 5 mins; then MIRM was measured as a function of time after switching off the field.…”

“…These compounds crystallizing in Immm-type orthorhombic structure has been of special interest in the field of magnetism for over a quarter century for anomalies associated with Haldane spin-chain gap and magnetic ordering of Ni and (magnetic-moment containing) R ions at the same temperature (see, for instance, Refs. [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Though this family has been considered to be prototype for Haldane spin-chain behavior, there was very little focus to understand magnetoelectric behavior of these insulators till recently.…”

Magnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5

“…Recently, we carried out exhaustive investigations 4-8 on many heavy rare-earth members of this family (R = Gd, Dy, and Er), bringing out new interesting properties, for example, (i) an additional magnetic transition at temperatures far below respective Néel temperature (T N ), (ii) magnetoelectric coupling, and (iii) not so-commonly known 're-entrant multiglass-like' behavior, that too of unusual types. 5,7 We also brought out magnetic-field-induced metamagnetic transitions and associated magnetodielectric (MDE) coupling effects. We therefore considered it worthwhile to subject one of the light rare-earth members, e.g., Nd 2 BaNiO 5 , for similar investigations for exploration of these anomalies in light rare-earth members of this family.…”

“…This situation is completely different from that observed for heavy rare-earth members. 5,7,8 In case of heavy rare-earth members in this series [see Fig. 3 in Refs.…”