COUPLING OF METAL-INSULATOR AND ANTIFERROMAGNETIC TRANSITIONS IN THE HIGHLY CORRELATED ORGANIC CONDUCTOR INCORPORATING MAGNETIC ANIONS, LAMBDA -BETS2F EBRXCL4-X BETS=BIS(ETHYLENEDITHIO)TETRASELENAFULVALENE
COUPLING OF METAL-INSULATOR AND ANTIFERROMAGNETIC TRANSITIONS IN THE HIGHLY CORRELATED ORGANIC CONDUCTOR INCORPORATING MAGNETIC ANIONS, LAMBDA -BETS2F EBRXCL4-X BETS=BIS(ETHYLENEDITHIO)TETRASELENAFULVALENE
复制标题
包含磁性阴离子的高度相关有机导体中金属-绝缘体和反铁磁跃迁的耦合，LAMBDA -BETS2F EBRXCL4-X BETS=双(亚乙基二硫)四硒富瓦烯
DOI：
10.1103/physrevb.58.9294
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发表时间：
1998
影响因子：
3.7
通讯作者：
P. Cassoux
中科院分区：
文献类型：
--
作者：
H. Akutsu;K. Kato;E. Ojima;H. Kobayashi;Hisashi Tanaka;A. Kobayashi;P. Cassoux
通过控制 Br 含量 (x)，研究了一系列包含磁性离子（Fe 3+ 且 S= 5 2）、λ− BETS 2 FeBr x Cl 4− x [B E T S= bi s (乙二硫基)四硒富瓦烯，x= 0–0.8] 的高度相关的二维有机 π 导体的电学和磁学性质。宽电阻率最大值出现在 100 (x≈ 0)–50 K (x≈ 0. 7) 处，表明 π 传导电子的强相关性随着 x 的增加而变得突出。同时，金属-绝缘体 (MI) 转变温度 (T MI) 从 8.5 (x= 0) 增加到 18 K (x= 0.7)。 x= 0.8 的晶体在 20 K 左右显示出半导体-绝缘体转变。在 0< x< 0.2 时，MI 转变和反铁磁 (AF) 转变在 8.5 K 左右协同发生 (T N≈ T MI)。在 T MI 处观察到平行于 c 轴的磁场 (H∥ c) 出现较大的磁化强度下降，这表明出现了局域 π 自旋 (S= 1 2) 以及 π 和 d 自旋系统的强 AF 耦合。对于 0.3< x< 0.5，在磁化强度-温度 (MT) 曲线中观察到两个异常。高温异常对应于MI跃迁(T MI)，低温异常对应于Fe 3+ 自旋的AF排序(T N)。在这种情况下，在 T MI 处观察到的相对较小的磁化强度下降表明 π 和 d 自旋系统之间存在较小的耦合。当 x > 0.6 时，T MI 处的磁化强度下降消失，这表明 π 和 d 电子系统解耦，并且 π 电子系统独立于 d 自旋系统进行 MI 跃迁。 T MI 处磁化率异常的消失表明π电子系统在T MI 以下转变为非磁绝缘态。另一方面，观察到显示Fe自旋的AF自旋结构的发展的M的各向异性，与x无关(0<x<0.8)。在 x= 0.3− 0. 5 附近，AF 自旋结构的易轴方向从平行于 c 轴（x< 0.2）变为垂直于 c 轴（x> 0.6）。换句话说，易磁化轴的方向根据 π− d 耦合的大小而变化。磁阻测量表明，λ− BETS 2 FeBr 0.7 Cl 3.3 的 T MI 几乎与 1 kbar 以下的磁场无关。但在高压下观察到类似于 λ− BETS 2 FeCl 4 的场恢复高导电状态。根据 T MI< T< 30 K 时的 M− T 曲线估算的 Weiss 温度 (θ) 随着 x 的增加而降低。
The electric and magnetic properties of a series of highly correlated two-dimensional organic π conductors incorporating magnetic ions (Fe 3+ with S= 5 2), λ− BETS 2 FeBr x Cl 4− x [B E T S= b i s (ethylenedithio) tetraselenafulvalene, x= 0–0.8] were examined by controlling the Br content (x). A broad resistivity maximum at 100 (x≈ 0)–50 K (x≈ 0. 7) indicating the strong correlation of π conduction electrons becomes prominent with increasing x. At the same time the metal-insulator (MI) transition temperature (T MI) increases from 8.5 (x= 0) to 18 K (x= 0.7). The crystal with x= 0.8 shows a semiconductor-insulator transition around 20 K. At 0< x< 0.2, the MI transition and the antiferromagnetic (AF) transitions take place cooperatively around 8.5 K (T N≈ T MI). A large magnetization drop was observed at T MI for the magnetic field parallel to the c axis (H∥ c), which indicates the appearance of localized π spins (S= 1 2) and a strong AF coupling of π and d spin systems. For 0.3< x< 0.5, two anomalies were observed in the magnetization-temperature (M− T) curve. The high-temperature anomaly corresponds to a MI transition (T MI) and the low-temperature one corresponds to an AF ordering of the Fe 3+ spins (T N). In this case, the relatively small magnetization drop observed at T MI suggests a small coupling of π and d spin systems. For x> 0.6, the magnetization drop at T MI disappeared, which shows that the π and d electron systems are decoupled and the π electron system undergoes MI transition independently of the d spin systems. The disappearance of the susceptibility anomaly at T MI indicates that the π electron system transforms to a nonmagnetic insulating state below T MI. On the other hand, the anisotropy of M showing the development of a AF spin structure of the Fe spins was observed independently of x (0< x< 0.8). Around x= 0.3− 0. 5, the direction of the easy axis of the AF spin structure changes from parallel to the c axis (x< 0.2) to perpendicular to it (x> 0.6). In other words, the direction of easy axis is varied according to the magnitude of π− d coupling. Magnetoresistance measurements showed that T MI of λ− BETS 2 FeBr 0.7 Cl 3.3 is almost independent of the magnetic field below 1 kbar. But a field-restored highly conducting state similar to that of λ− BETS 2 FeCl 4 was observed at high pressure. The Weiss temperature (θ) estimated from the M− T curve at T MI< T< 30 K decreases with increasing x.