The Spontaneous Exchange Bias Effect on La 1.5 Ba 0.5 CoMnO 6
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The Spontaneous Exchange Bias Effect on La1.5 Ba0.5 CoMnO6 M. Boldrin1 · L. T. Coutrim1 · L. Bufaic¸al1 Received: 22 June 2020 © Sociedade Brasileira de F´ısica 2020
Abstract La1.5 Ba0.5 CoMnO6 is a re-entrant cluster glass material exhibiting a robust negative exchange bias (EB) effect even after being cooled from an unmagnetized state down to low temperature in zero magnetic field. Here we thoroughly investigate this phenomena by performing magnetization as a function of applied field [M(H )] measurements at several different temperatures and maximum applied magnetic fields (Hm ). The spontaneous EB (SEB) effect is observed below 20 K, and shows a maximum value for Hm = 75 kOe. The effect is greatly enhanced when the M(H ) curves are measured after the system is cooled in the presence of a magnetic field. The asymmetry of the M(H ) curves here investigated can be well described by a recently proposed model based on the unconventional relaxation of the SG-like moments during the hysteresis cycle. Keywords Exchange bias · Spin glass · Double-perovskite · Transition-metals
1 Introduction There is a great interest in the exchange bias (EB) effect due to its potential applicability in high-density magnetic recording, giant magnetoresistance and spin valve devices. Conventionally, the unidirectional anisotropy (UA) across a ferromagnetic (FM)-antiferromagnetic (AFM) interface is set by cooling the system in the presence of an external magnetic field (H ) [1]. Conversely, for the spontaneous EB (SEB) effect, the asymmetry in the hysteresis loop is observed at low temperatures (T ) even after the system is cooled in zero H [2–5]. For many of the materials presenting this recently discovered phenomena, the presence of a re-entrant spin glass (RSG) state, where a spin glass (SG)-like phase is concomitant to other conventional magnetic phases [6], seems to play a key role [7, 8]. In this context, the double-perovskite (DP) compounds are prospective candidates to exhibit SEB since its intrinsic structural disorder usually leads to competing magnetic interactions and frustration, the key ingredients for the emergence of SG-like behavior [6].
L. Bufaic¸al
[email protected] 1
Instituto de F´ısica, Universidade Federal de Goi´as, Goiˆania, GO 74001-970, Brazil
From the SEB materials discovered so far, the great majority are perovskites [3, 5, 9–12]. The La1.5 Sr0.5 CoMnO6 (LSCMO) DP stands out as presenting the largest SEB already known [11], while for the sister compound La1.5 Ca0.5 CoMnO6 (LCCMO) the effect is very subtle [12]. Although the presence of SG-like phase is established as requisite for the observation of the phenomena in LSCMO, LCCMO and other related compounds [7, 8], the microscopic mechanisms responsible for it are not completely known yet. It is not clear, for instance, why similar compounds as LSCMO and LCCMO exhibit such different SEB effects, and also why the phenomena is not observed for some other RSG DP compounds. In order to get insight into this question, a detailed investigation
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