TY - JOUR

T1 - Site dilution study of a square lattice Heisenberg antiferromagnet with S = 5/2 covering the percolation threshold

AU - Takeda, Kazuyoshi

AU - Fujita, Osamu

AU - Hitaka, Masako

AU - Mito, Masaki

AU - Kawae, Tatsuya

AU - Higuchi, Yoshihiro

AU - Deguchi, Hiroyuki

AU - Muraoka, Yoshinori

AU - Zenmyo, Kazuko

AU - Kubo, Hidenori

AU - Tokita, Masahiko

AU - Yamagata, Kazuo

N1 - Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.

PY - 2000/11

Y1 - 2000/11

N2 - 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.

AB - 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.

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U2 - 10.1143/JPSJ.69.3696

DO - 10.1143/JPSJ.69.3696

M3 - Article

AN - SCOPUS:0034550471

VL - 69

SP - 3696

EP - 3703

JO - Journal of the Physical Society of Japan

JF - Journal of the Physical Society of Japan

SN - 0031-9015

IS - 11

ER -