Magnetic properties and electron spin resonance of charge ordering manganite Y 0.5 Ca 0.5 MnO 3 H.W. Tian, W.T. Zheng * , Z.D. Zhao, T. Ding, S.S. Yu, B. Zheng, X.T. Li, F.L. Meng, Q. Jiang Key Lab of Automobile Materials of MOE, Department of Materials Science, Jilin University, Qianwei Road 10, Changchun 130012, PR China Received 19 October 2004; in final form 24 November 2004 Available online 15 December 2004 Abstract We report the magnetization and electron spin resonance study on charge-ordering (CO) manganite Y 0.5 Ca 0.5 MnO 3 (YCMO) across the charge-ordering transition temperature T CO down to the antiferromagnetic ordering transition temperature T N . The tran- sition temperatures of T CO and T N are observed at 275 and 125 K, respectively. The observed large decrease in the linewidth from T N to T CO can be explained in terms of motional narrowing caused by the hopping of the Jahn–Teller (JT) polarons. Below T CO the g-value is almost constant, suggesting the weakening of orbital order in the compound of YCMO. Ó 2004 Elsevier B.V. All rights reserved. 1. Introduction Hole-doped perovskite manganites exhibit a multi- tude of magnetic, electronic and structural phase transi- tions as functions of doping level, temperature, etc. [1] and have attracted a great deal of attention due to the anomalously large negative ÔcolossalÕ magnetoresistance (CMR) [2–5]. Understanding the behavior of these Mn- based materials is a challenge for both experimentalists and theorists. Although most of the attention has been focused on the effect of applied magnetic field and tem- perature on the conductivity, there is much to be learned from studies of the spin-dependent properties through measurements of the static and dynamic spin susceptibil- ities as well the electron spins [6]. Since electron spin resonance (ESR) can directly probe the electron spins, a lot of ESR studies have al- ready been carried out. The spin clusters and the inho- mogeneous nature of the doped manganites have been supported by some ESR work [7–11]. However, these reports about ESR experimental studies concentrated on the manganites across the metal–insulator transition and at high temperature. To our knowledge, there have been few studies about Y 0.5 Ca 0.5 MnO 3 (YCMO) across the charge-ordering (CO) transition, although those of Pr 0.6 Ca 0.4 MnO 3 (PCMO) [12] and Nd 0.5 Ca 0.5 MnO 3 (NCMO) [13] have been reported. It should point out that the similar material Tb 0.5 Ca 0.5 MnO 3 (TCMO) to YCMO has been studied in detail by Blasco et al. [14]. Since Tb and Y have similar ionic radius in their own manganites, the magnetic properties of TCMO will bear some analogy to those of YCMO. The ESR exper- iments of Y 1x Ca x MnO 3 manganites have been per- formed by Agu ¨ero et al. [15] recently. For x = 0.5, the linewidth DH pp is approximately 2500 Gauss for the YCMO sample [15]. Joshi et al. [13] have observed that the ESR linewidth decreases as the temperature is in- creased in the temperature range T N –T CO for the PCMO and NCMO samples, which can be taken as the fingerprints of the CO state in manganites. How- ever, Arulraj et al. [16] have reported that as the tem- perature is increased for YCMO sample, there is not any perceptible change in linewidth at T CO , and the 0009-2614/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2004.11.129 * Corresponding author. Fax: +86 431 5168246. E-mail address: wtzheng@jlu.edu.cn (W.T. Zheng). www.elsevier.com/locate/cplett Chemical Physics Letters 401 (2005) 585–589