Swiatkowska-Warkocka et al. Nanoscale Research Letters 2011, 6:226 http://www.nanoscalereslett.com/content/6/1/226 N A N O E X P R E S S Open Access Controlling exchange bias in Fe O /FeO 3 4 composite particles prepared by pulsed laser irradiation Zaneta Swiatkowska-Warkocka*, Kenji Kawaguchi, Hongqiang Wang, Yukiko Katou, Naoto Koshizaki Abstract Spherical iron oxide nanocomposite particles composed of magnetite and wustite have been successfully synthesized using a novel method of pulsed laser irradiation in ethyl acetate. Both the size and the composition of nanocomposite particles are controlled by laser irradiation condition. Through tuning the laser fluence, the Fe3O4/ FeO phase ratio can be precisely controlled, and the magnetic properties of final products can also be regulated. This work presents a successful example of the fabrication of ferro (ferri) (FM)/antiferromagnetic (AFM) systems with high chemical stability. The results show this novel simple method as widely extendable to various FM/AFM nanocomposite systems. Introduction Magnetic nanoparticles and hybrid magnetic nanostruc- tures are of growing interest because of their technologi- cal applications in magnetic recording media, sensitive magnetic sensors and various biomedical applications such as drug delivery system, hyperthermia or magnetic resonance imaging [1]. In order to fulfil the require- ments of many of these applications, an accurate control over the coercivity is strongly required. Exchange bias coupling at the ferro (ferri) (FM)/anti- ferromagnetic (AFM) interface has attracted consider- able attention due to their applications in permanent magnet applications and high density recording media [2,3]. The exchange bias effect is manifested by the shifting and broadening of a magnetic hysteresis loop of a sample cooled under an applied field [1,4,5]. Although the intrinsic origin of exchange bias effect is not yet understood fully, it is generally accepted that the inter- face exchange coupling between FM and AFM is the origin of the exchange bias [6]. Exchange bias has been extensively studied in bilayer and multilayer thin films [7,8], nanoparticles with core/ shell structure [9-11] and particles dispersed in matrix [12]. However, to date, the report about how to control * Correspondence: zaneta.swiatkowska@aist.go.jp Nanosystem Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, 305-8565 Ibaraki, Japan the exchange bias by changing the FM/AFM ratio is seldom. So far, various experimental methods have been used to produce FM/AFM heterostructure particles, e.g. che- mical and thermal decomposition [10,13,14], ball milling method [11], gas condensation and chemical vapour deposition [15,16]. However, decomposition methods need the chemicals which often cannot be removed and remain as residual molecules on particle surfaces. Gas- phase methods require expensive and large-scale vacuum equipments. Such methods are generally effec- tive for preparing particles with a narrow size distribu- tion. However, most of these approaches are limited to synthesizing particles with a diameter smaller than 30 nm. Additionally, most of mentioned methods lead to the sintering of two phases and the poor quality of the interface. This has been attributed to the weak interfa- cial interaction between the FM and AFM phases in particles and results in a weak exchange bias. Therefore, the development of new synthetic techniques for FM/ AFM particles with high exchange bias is still a target of current research. In this study, we demonstrate a novel method for pre- paring submicrometer iron oxide nanocomposite spheri- cal particles by pulsed laser irradiation in liquid (PLIL). In contrast to the pulsed laser ablation in liquid using a focused laser beam, which has been widely studied, PLIL irradiating source particles dispersed in liquid with © 2011 Swiatkowska-Warkocka et al; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.