Research articles Possible observation of Grifﬁth phase over large temperature range in plasma sintered La 0.67 Ca 0.33 MnO 3 D.K. Mishra a,⇑ , B.K. Roul b , S.K. Singh c , V.V. Srinivasu d a Department of Physics, Faculty of Engineering and Technology (ITER), Siksha ‘O’ Anusandhan University, Khandagiri Square, Bhubaneswar 751030, Odisha, India b Institute of Materials Science, Planetarium Building, Bhubaneswar 751013, Odisha, India c Advanced Materials Technology Department, Institute of Minerals and Materials Technology (CSIR), Bhubaneswar 751013, Odisha, India d Department of Physics, College of Science, Engineering and Technology, University of South Africa, Johannesburg 1710, South Africa article info Article history: Received 10 February 2017 Received in revised form 31 May 2017 Accepted 13 June 2017 Available online xxxx Keywords: Grifﬁth phase Curie temperature Plasma sintering ESR EPMA, LCMO abstract We report on the possible observation of Grifﬁth phase in a wide range of temperature (>272–378 K) in the 2.5 min plasma sintered La 0.67 Ca 0.33 MnO 3 (LCMO) as deduced from careful electron spin resonance studies. This is 106 K higher than the paramagnetic to ferromagnetic transition (Curie transition 272 K) temperature. The indication of Grifﬁth phase in such a wide range is not reported earlier by any group. We purposefully prepared LCMO samples by plasma sintering technique so as to create a dis- ordered structure by rapid quenching which we believe, is the prime reason for the observation of Grifﬁth Phase above the Curie transition temperature. The inverse susceptibility curve represents the existence of ferromagnetic cluster in paramagnetic region. The large resonance peak width (40–60 mT) within the temperature range 330–378 K conﬁrms the sample magnetically inhomogeneity which is also estab- lished from our electron probe microstructure analysis (EPMA). EPMA establishes the presence of higher percentage of Mn 3+ cluster in comparison to Mn 4+ . This is the reason for which Grifﬁth state is enhanced largely to a higher range of temperature. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction The understanding of spin dynamics, magnetic interactions and spin correlation on a microscopic level could be well explained in colossal magnetoresistance (CMR) manganites through electron spin resonance studies [1–4]. The interplay between spin and charge degrees of freedom in colossal magnetoresistance mangan- ites have been generated a lot of attention for the potential appli- cations of these materials in magnetic sensors, bolometers, magnetic refrigeration and micro-magneto electronics (micro- spintronic devices) [5–8]. The prime interest in manganites is also to observe the low-ﬁeld sensitivity of large magnetoresistance (MR) response around Curie temperature (T C ) close to room tem- perature. The Curie temperature observed in La 0.67 Ca 0.33 MnO 3 (LCMO) is 250 K whereas it could be enhanced to 260 K in LCMO sintered at partial melted stage [9]. The micrographs of partial- melt samples exhibit an excellent connectivity between grains, suggesting the enhancement of percolation current transport by opening new conduction channels and disappearance of magnetic phase boundary at elevated temperatures by the ordering of Mn spins blocked at the grain boundary of sintered samples [9]. This new phenomena prompts us to sinter the sample by thermal plasma technique within a short sintering time, which leads to the enhancement of Curie transition temperature from 260 K to 280 K [10]. Thermal plasma techniques forbids the grain growth and as well creates inter-grain and intra-grain connection between them which is the prime reason for the enhancement of Curie tran- sition temperature. In addition to this, the understanding of Grif- ﬁth phase in the paramagnetic region is an interesting issue in manganites. However, ESR studies conﬁrm the presence of Grifﬁth Phase [11] in the paramagnetic region upto higher temperature than the Curie transition temperature in manganites [1,5,12–22] and in particular LCMO [1,8,14,17]. The quenched disordered struc- ture and clusters of magnetic domains on sample surface is the ori- gin of enhanced Grifﬁth phase to higher temperature [11,16]. It is reported that Grifﬁth phase is observed within a temperature range of 20–30 K higher than the paramagnetic to ferromagnetic transition temperature. Moreover, the investigations suggest that the mixture of Mn 3+ /Mn 4+ ions and the arrangement of both the ions are responsible for the observation of enhanced Grifﬁth phase at large temperature above than Curie transition temperature. Again the presence of some form of magnetic clusters is also responsible for the enhancement of ferromagnetic signal above http://dx.doi.org/10.1016/j.jmmm.2017.06.075 0304-8853/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: dilipiuac@gmail.com (D.K. Mishra). Journal of Magnetism and Magnetic Materials xxx (2017) xxx–xxx Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm Please cite this article in press as: D.K. Mishra et al., Possible observation of Grifﬁth phase over large temperature range in plasma sintered La 0.67 Ca 0.33 - MnO 3 , Journal of Magnetism and Magnetic Materials (2017), http://dx.doi.org/10.1016/j.jmmm.2017.06.075