* Corresponding author. Fax: #81-22-217-6475. E-mail address: nakano@msp.phys.tohoku.ac.jp (T. Nakano) Physica B 281&282 (2000) 688}690 Loading density dependence of ferromagnetic properties in potassium clusters arrayed in a simple cubic structure in zeolite LTA Takehito Nakano*, Yuka Ikemoto, Yasuo Nozue Department of Physics, Microstructure Physics Group, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan CREST, Japan Science and Technology Corporation (JST), Japan Center for Interdisciplinary Research, Tohoku University, Japan Abstract Magnetic properties are investigated for potassium clusters arrayed in zeolite LTA. The potassium loading density per cluster, n, is changed up to 7.2 per cluster. The n-dependence of the Curie constant and the magnetization are measured in detail. Possible origins of ferromagnetic properties are discussed.  2000 Elsevier Science B.V. All rights reserved. Keywords: Ferromagnetism; Zeolite; Alkali metal cluster Recently, magnetically ordered states are found in alkali-metal clusters arrayed in zeolites, such as a ferromagnetism in K clusters in LTA (simple cubic struc- ture) [1] and an antiferromagnetism in Na clusters in SOD (body centered cubic structure) [2]. These results demonstrate that s-electron systems can be magnetic materials, when the localized character and the mutual interaction are given properly to clusters by con"ning s-electrons in the regular space of zeolite crystals. In LTA, the -cages with the inside diameter of &11 A s are arrayed in a simple cubic structure, as shown in Fig. 1. The lattice constant is 12.3 A s . In K-form LTA, the framework Al  Si  O  is negatively charged and K cations are distributed in the space of the framework. Cationic K-clusters can be generated in -cages by the loading of guest K metal. The number of 4s electrons, n, can be controlled up to &7.2 per -cage (or cluster). These 4s electrons successively occupy the 1s- and 1p-quantum electronic states of cluster depending on n, i.e. "rst two for 1s- and next six for 1p-state [3]. Fer- romagnetic properties are observed most remarkably at the middle loading density n+5 [4]. The coexistence of the spontaneous magnetization and the negative Weiss temperature can be explained tentatively by the model of ferrimagnetism [5]. The spontaneous magnetization is observed, when n exceeds 2, indicating that the 1p state of clusters plays an essential role in the ferromagnetic prop- erties [6]. With increasing n for n'4, the Curie and Weiss temperatures gradually approach zero Kelvin with increasing n to 7.2 [7]. K clusters in LTA is thought to be insulating at any value of n, because of the absence of the Drude term in the infrared absorption spectra [5}7]. Thus, resultant materials are assigned to the Mott insula- tor. Very recently, a structural analysis is given for these materials [8,9]. In this paper, an n-dependence of the magnetic pro- perties is investigated in detail for the full range of n. A discussion is given for the plausible origins of the spontaneous magnetization, such as a spin canting of antiferromagnetic phase, a ferrimagnetism, and a fer- romagnetism with an orbital ordering. Distilled potassium was adsorbed into fully dehy- drated K-form LTA powder through the vapor phase in a quartz glass tube. The loading density n was estimated from the optical analysis normalized by the chemical analysis [3]. Magnetic measurements were performed by using a SQUID system (quantum design) and the 0921-4526/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 1 1 0 0 - X