结构无序磁体的有效临界行为与渐近临界行为
Effective and asymptotic criticality of structurally disordered magnets
AI总结：
本文通过随机自旋长度伊辛模型证明结构无序磁体与位点稀释伊辛模型属于同一普适类，并利用场论重整化群揭示了由磁性组分性质差异决定的有效临界行为。
摘要：
淬火结构无序磁体磁临界行为的变化通常在实验和蒙特卡洛模拟中以由磁性组分和非磁性组分构成的稀释系统为例加以展示。我们的研究旨在表明，类似效应不仅可以在含非磁性杂质的稀释磁体中观察到，也可以通过存在两种（及更多）化学上不同的磁性组分来实现。为此，我们考虑一个结构无序淬火磁体模型，其中所有晶格位点都被不同长度 $L$ 的伊辛型自旋占据。在这种随机自旋长度伊辛模型中，每个自旋的长度 $L$ 是由分布函数 $p(L)$ 支配的随机变量。我们证明该模型属于位点稀释伊辛模型的普适类。这证明两个模型由相同的渐近临界指数值描述。然而，它们的有效临界行为不同。作为案例研究，我们考虑两种不同磁体的淬火混合物，其基本磁矩值分别为 $L_1=1$ 和 $L_2=s$，浓度分别为 $c$ 和 $1-c$。我们应用场论重整化群方法来分析由 $s$ 和 $c$ 触发的不同初始条件下的重整化群流，并计算远离重整化群变换不动点处的有效临界指数。我们展示了有效指数如何受磁性组分性质差异的支配。
英文摘要：
Changes in magnetic critical behaviour of quenched structurally-disordered magnets are usually exemplified in experiments and in MC simulations by diluted systems consisting of magnetic and non-magnetic components. By our study we aim to show, that similar effects can be observed not only for diluted magnets with non-magnetic impurities, but may be implemented, e.g., by presence of two (and more) chemically different magnetic components as well. To this end, we consider a model of the structurally-disordered quenched magnet where all lattice sites are occupied by Ising-like spins of different length $L$. In such random spin length Ising model the length $L$ of each spin is a random variable governed by the distribution function $p(L)$. We show that this model belongs to the universality class of the site-diluted Ising model. This proves that both models are described by the same values of asymptotic critical exponents. However, their effective critical behaviour differs. As a case study we consider a quenched mixture of two different magnets, with values of elementary magnetic moments $L_1=1$ and $L_2=s$, and of concentration $c$ and $1-c$, correspondingly. We apply field-theoretical renormalization group approach to analyze the renormalization group flow for different initial conditions, triggered by $s$ and $c$, and to calculate effective critical exponents further away from the fixed points of the renormalization group transformation. We show how the effective exponents are governed by difference in properties of the magnetic components.
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