Site dilution study of a square lattice Heisenberg antiferromagnet with S = 5/2 covering the percolation threshold

Kazuyoshi Takeda, Osamu Fujita, Masako Hitaka, Masaki Mito, Tatsuya Kawae, Yoshihiro Higuchi, Hiroyuki Deguchi, Yoshinori Muraoka, Kazuko Zenmyo, Hidenori Kubo, Masahiko Tokita, Kazuo Yamagata

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Abstract

The site dilution problems on a square lattice antiferromagnet with spin S = 5/2, Mn(HCOO)22(NH2)2CO (TN = 3.77K), have been studied for a wide range of magnetic concentration x, covering the percolation threshold xp = 0.59 for the square lattice, by the measurements of magnetic heat capacity and susceptibility. The Néel temperature TN(x) has been found to decrease as d/dx{TN(x)/TN(1)} = R = 2.7 just below x = 1 for the three kinds of non-magnetic impurities, Mg2+(2p6), Zn2+(3d10) and Cd2+(4d10), at almost the same reduction rate as in the cases of the antiferromagnet K2MnF4 with S = 5/2 and the ferromagnet K2CuF4 with S = 1/2. The present value R = 2.7, however, makes a contrast to R = 3.1 for the diluted La2CuO4, an S = 1/2 Heisenberg antiferromagnet. The extrapolation of TN(x), with R = 2.7(3.1) down to TN(x) = 0 gives a pseudo-critical concentration x = xc = 0.63(0.68) deviating from xp = 0.59. This indicates that TN(x) must draw concavely near TN (xp) = 0 at low temperatures, making a contrast to the convex curve of decreasing TN(x) down to zero at x = xp for Ising systems. As x decreases, dilution effects reflected on the reduction of lattice dimensionality, the Curie-Weiss temperature and the Curie constant are discussed on the base of the absolute values of the magnetic heat capacity and susceptibility. An anomalous enhancement of the heat capacities has been found in the external field of 50 kOe for the system with x = 0.12, which was theoretically reproduced by the contribution from isolated ions and clusters computer-generated on the square lattice with the same magnetic concentration.

Original languageEnglish
Pages (from-to)3696-3703
Number of pages8
Journaljournal of the physical society of japan
Volume69
Issue number11
DOIs
Publication statusPublished - Nov 2000

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)

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    Takeda, K., Fujita, O., Hitaka, M., Mito, M., Kawae, T., Higuchi, Y., Deguchi, H., Muraoka, Y., Zenmyo, K., Kubo, H., Tokita, M., & Yamagata, K. (2000). Site dilution study of a square lattice Heisenberg antiferromagnet with S = 5/2 covering the percolation threshold. journal of the physical society of japan, 69(11), 3696-3703. https://doi.org/10.1143/JPSJ.69.3696