Magnetic ordering in a genuine organic crystal with triangular antiferromagnetic spin units
Magnetic ordering in a genuine organic crystal with triangular antiferromagnetic spin units
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DOI：
10.1103/physrevb.72.024435
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发表时间：
2005-07
影响因子：
3.7
通讯作者：
K. Takeda*;Y. Yoshida;Y. Inanaga;T. Kawae;D. Shiomi;T. Ise;M. Kozaki;K. Okada;Kazunobu Sato;T. Takui
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文献类型：
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作者：
K. Takeda*;Y. Yoshida;Y. Inanaga;T. Kawae;D. Shiomi;T. Ise;M. Kozaki;K. Okada;Kazunobu Sato;T. Takui
研究了反铁磁三角自旋单元 N,N,N-三[对-(N-氧基-四丁氨基)苯基]胺的真正有机自由基晶体的典型磁性行为。磁化率测量表明，当温度冷却至约100℃时，分子内实现了基态双峰，给出了每个分子在较低温度下的有效自旋值。下面，磁化率呈铁磁性增加至 ，随后在较低温度下反铁磁性降低。对热容和磁化强度的磁场依赖性的分析表明，分子间铁磁和反铁磁相互作用分别以 和 的值起作用，这合理地解释了场中转变温度的观测值：这表明，在 Rushbrooke-Wood 预测的各向同性海森堡自旋系统的温度下，有机磁体有序，不仅包括目前的三自由基 系统，而且还包括最典型的单自由基和双自由基有机铁磁体。获得完全映射的温度-磁场相边界，并通过单个公式来描述，其值为 、 、 、 和 ，其中，其上没有任何双临界点存在的痕迹，如具有单轴各向异性的普通反铁磁体中所见。讨论了各向异性极小的非受抑反铁磁体的临界指标。
A typical magnetic behavior has been studied in a genuine organic radical crystal of antiferromagnetic triangular spin units, N,N,N-Tris[p-(N-oxyl-tetra-butyamino)phenyl]amine. The magnetic susceptibility measurements indicate that a ground-state doublet is achieved within a molecule when the temperature is cooled down to aboutfrom, giving the effective spin value of each molecule at lower temperatures to be. Below, the magnetic susceptibility increases ferromagnetically down to, being followed by an antiferromagnetic decrease at lower temperatures. The analyses of the magnetic field dependence of heat capacity and magnetization reveals that the intermolecular ferromagnetic and antiferromagnetic interactions are working with the respective valueand, which reasonably explains the observed value of the transition temperatureat the field: It is suggested that organic magnets order at the temperature predicted by Rushbrooke–Wood for isotropic Heisenberg spin systems, including not only the present tri-radical system, but also to the most typical genuine organic ferromagnets of mono-radicaland biradical. A fully mapped temperature-magnetic field phase boundary is obtained to be described by a single formulawith the values,,, and, where, without any trace of the existence of the bicritical point on it as seen in normal antiferromagnets with uniaxial anisotropy. It is discussed that the critical indices may beandfor nonfrustrated antiferromagnets with infinitesimally small anisotropy.