Magnetic properties of σ- and hexagonal-Mn76Si18Cr6 approximant phases of a dodecagonal quasicrystal
Magnetic properties of σ- and hexagonal-Mn76Si18Cr6 approximant phases of a dodecagonal quasicrystal
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十二方准晶的σ-和六方-Mn76Si18Cr6近似相的磁性
DOI：
10.1103/physrevb.84.224201
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发表时间：
2011
影响因子：
3.7
通讯作者：
J.Dolin〓ek
中科院分区：
文献类型：
--
作者：
S.Kashimoto;A.Kocjan;Z.Jagli〓i〓;S.Jazbec;H.Iga;T. Ishimasa;J.Dolin〓ek
Mn-Si-V（Cr）过渡金属-合金体系中的四方σ相和六方（hex）相是可以大量制备的十二面（12倍）准晶的稳定近似相。我们合成了mnsico的σ相和六相样品，并测定了它们的磁性能。σ-MnSiCr在≈8 K以下发生了自旋冻结向标准自旋玻璃相的转变，其特征是零场冷却磁化率达到最大值，交流磁化率出现频率相关的尖峰，磁滞和热磁化强度的超低时间衰减。相比之下，在最低温度为2 K的六相mnsicr中没有观察到自旋玻璃化转变。磁化率分析表明，两相的自旋耦合是反铁磁的，但σ相的耦合强度要强得多。由于这两种相在结构上都是由与十二角准晶体相关的三角形-正方形平铺方案描述的，这对三角形施加了afm耦合自旋的几何挫折，因此六棱形mnsicr中没有自旋-玻璃转变可能是由于这种转变在实验设置的最低温度以下发生了转移，这是由于六棱形相中较弱的自旋耦合和较小的矩大小。在这两种样品中，在磁信号中都检测到在≈42 K时向铁磁相转变的微小mno夹杂物。放置在三角形-正方形平铺顶点的原子力显微镜耦合自旋之间相互作用的几何挫败应该是十二角体准晶体及其近似体的一般特征，因此自旋玻璃型排序预计在十二角体相中很常见。
The tetragonal σ phase and the hexagonal (hex) phase in the Mn-Si-V(Cr) transition-metal-alloy systems are stable approximant phases of a dodecagonal (12-fold) quasicrystal that can be prepared in bulk quantities. We have synthesized samples of the σ andhexphases of composition MnSiCrand determined their magnetic properties. In the σ-MnSiCr, a spin-freezing transition to a canonical spin-glass phase was detected below≈ 8 K, characterized by a maximum in the zero-field-cooled susceptibility, a frequency-dependent cusp in the ac susceptibility,hysteresis, and ultraslow time decay of the thermoremanent magnetization. In contrast, no spin-glass transition was observed in thehex-MnSiCrphase down to the lowest investigated temperature of 2 K. The analysis of the susceptibility has shown that the coupling of spins in both phases is antiferromagnetic (AFM), but the coupling strength is considerably stronger in the σ phase. Since both phases are structurally described by the triangle-square tiling scheme related to that of the dodecagonal quasicrystal, which imposes geometric frustration of the AFM-coupled spins on triangles, the absence of spin-glass transition in thehex-MnSiCrcould be due to shifting of this transition below the lowest temperature of our experimental setup, as a consequence of weaker spin coupling and smaller moment sizes in thehexphase. In both investigated samples, tiny MnOinclusions that undergo a transition to a ferrimagnetic phase at≈ 42 K were detected in the magnetic signal. Geometric frustration of interactions between the AFM-coupled spins placed at the vertices of the triangle-square tiling should be a general feature of dodecagonal quasicrystals and their approximants, so that spin-glass-type ordering is expected to occur quite commonly in the dodecagonal phases.