Critical Phenomena Study of 3D Heisenberg Magnet (original) (raw)

Prospects and Opportunities of 2D van der Waals Magnetic Systems

Annalen der Physik, 2020

The existence of spontaneous magnetization in low dimensional magnetic systems has attracted intensive studies since the early 60s and research remains very active even now. Only recently, magnetic van der Waals (vdW) systems down to a few layers have been broadly discussed for their magnetic order ground states at finite temperature. The naturally inherited layered structure of the vdW magnetic systems possessing onsite magnetic anisotropy from band electrons can suppress the long‐range fluctuations. This provides an excellent vehicle to study the transition of magnetism to 2D limits both theoretically and experimentally. Here the current status of 2D vdW magnetic system and its potential applications are briefly summarized and discussed.

The Magnetic Genome of Two-Dimensional van der Waals Materials

ACS Nano

Magnetism in two-dimensional (2D) van der Waals (vdW) materials has recently emerged as one of the most promising areas in condensed matter research, with many exciting emerging properties and significant potential for applications ranging from topological magnonics to low-power spintronics, quantum computing, and optical communications. In the brief time after their discovery, 2D magnets have blossomed into a rich area for investigation, where fundamental concepts in magnetism are challenged by the behavior of spins that can develop at the single layer limit. However, much effort is still needed in multiple fronts before 2D magnets can be routinely used for practical implementations. In this comprehensive review, prominent authors with expertise in complementary fields of 2D magnetism (i.e., synthesis, device engineering, magneto-optics, imaging, transport, mechanics, spin excitations, and theory and simulations) have joined together to provide a genome of current knowledge and a guideline for future developments in 2D magnetic materials research.

Complex critical magnetic behaviour in three dimensions

Journal of Magnetism and Magnetic Materials, 2007

Experimental results on the critical magnetic behaviour of magnets with a three-dimensional (3D) spin and isotropic 3D interactions are presented. It is observed that the critical behaviour can be rather complicated. This is because two magnetic order parameters can occur even in magnets with only one magnetic lattice site. The two order parameters must be attributed to an ordered longitudinal and transverse spin component meaning that the spin precession is elliptic rather than circular. Usually, one of the two order parameters is discontinuous at T c. Characteristic for this type of first-order phase transition is that the continuous part in the rise of the order parameter follows critical power law with exponent b and that the paramagnetic susceptibility diverges. The exponent g belongs not necessarily to the same universality class as b meaning that the scaling hypothesis can be violated. It appears necessary to distinguish between magnets with integer and half-integer spin. For magnets with integer spin, the critical exponent b is close to the Heisenberg value but for magnets with half-integer spin b is close to the Landau (mean field) value. The different critical behaviour seems to be associated with the opening of a magnetic excitation gap at T c for integer spin values while for half-integer spins the magnetic excitation spectrum is essentially continuous. The magnon gap of the magnets with integer spin is identified as a second-order parameter. The origin of the gap is a mystery. Discontinuous phase transitions and the appearance of a second-order parameter can be considered as signatures of higher order interactions such as four-spin interactions. Higher order interactions seem to be especially important in three dimensions.

Recent advances in two-dimensional van der Waals magnets

Microstructures, 2022

Two-dimensional (2D) magnets have evoked tremendous interest within the research community due to their fascinating features and novel mechanisms, as well as their potential applications in magnetic nanodevices. In this review, state-of-the-art research into the exploration of 2D magnets from the perspective of their magnetic interaction and order mechanisms is discussed. The properties of these magnets can be effectively modulated by varying the external parameters, such as the charge carrier doping, thickness effect, pressure and strain. The potential applications of heterostructures of these 2D magnets in terms of the interlayer coupling strength are reviewed, and the challenges and outlook for this field are proposed.

Dynamic critical behavior of disordered 3D Heisenberg ferromagnets

Journal of Magnetism and Magnetic Materials, 2001

The in#uence of a strong disorder on the critical dynamics of an 3D Heisenberg ferromagnet was investigated by high-resolution quasi-elastic neutron scattering. A new disordered-induced dynamical critical behavior was found, characterized by its critical exponent z"2.3. The dynamical scaling function appeared mainly una!ected by disorder but its description led to a new parameterization of the renormalization group theory, as in the case of pure nickel.

Recent breakthroughs in two-dimensional van der Waals magnetic materials and emerging applications

Nano Today, 2020

Two-dimensional (2D) magnetism is now the attention of central demands in fundamental condensed matter physics concerning about the understanding and control of new phases. The demonstration of ferromagnetism in an atomically thin layer develops the prospects for a variety of device applications of 2D van der Waals (vdW) materials. The long-range ferromagnetic ordering in 2D vdW crystals together with their fascinating electric and optical properties will lead to magnetic, magneto-electric, and magneto-optic applications. Low-power, high-speed, and ultra-compact spintronic devices, data storage, information recognition and processing, smart sensors, and quantum computing applications are highly necessary for future industrial applications. This review covers the fundamental chemical structures and synthesis methods of 2D magnetic materials, the techniques for characterizing magnetic properties, device applications and the challenges faced in this emerging field. The progress in both intrinsic and extrinsic magnetic 2D materials originated from external stimuli such as doping, defects, functionalization, and strain is emphasized. The comparison of fundamental physics, chemistry, and related issues of vdW 2D magnetic materials with other-dimensional counterparts concentrated on backgrounds is also emphasized. We focus on the design of chemical and crystal structures leading to 2D magnetism, detailed chemical and physical properties and the device applications of vdW 2D magnetism. Finally, challenges and outlooks in the realization of 2D magnetism are discussed and believed that this emerging field will excite more intensive research and provide exceptional breakthroughs in the field of spintronics.

Two‐Dimensional Magnets: Forgotten History and Recent Progress towards Spintronic Applications

Advanced Functional Materials, 2019

The recent discovery of 2D magnetic order in van der Waals materials has stimulated a renaissance in the field of atomically thin magnets. This has led to promising demonstrations of spintronic functionality such as tunneling magnetoresistance. The frantic pace of this emerging research, however, has also led to some confusion surrounding the underlying phenomena of phase transitions in 2D magnets. In fact, there is a rich history of experimental precedents beginning in the 1960s with quasi‐2D bulk magnets and progressing to the 1980s using atomically thin sheets of elemental metals. This review provides a holistic discussion of the current state of knowledge on the three distinct families of low‐dimensional magnets: quasi‐2D, ultrathin films, and van der Waals crystals. It highlights the unique opportunities presented by the latest implementation in van der Waals materials. By revisiting the fundamental insights from the field of low‐dimensional magnetism, this review highlights fa...

Effective critical behaviour of diluted Heisenberg-like magnets

Journal of Magnetism and Magnetic Materials, 2003

In agreement with the Harris criterion, asymptotic critical exponents of threedimensional (3d) Heisenberg-like magnets are not influenced by weak quenched dilution of non-magnetic component. However, often in the experimental studies of corresponding systems concentration-and temperature-dependent exponents are found with values differing from those of the 3d Heisenberg model. In our study, we use the field-theoretical renormalization group approach to explain this observation and to calculate the effective critical exponents of weakly diluted quenched Heisenberg-like magnet. Being non-universal, these exponents change with distance to the critical point T c as observed experimentally. In the asymptotic limit (at T c) they equal to the critical exponents of the pure 3d Heisenberg magnet as predicted by the Harris criterion.

Pervasive beyond Room-Temperature Ferromagnetism in a Doped van der Waals Magnet

Physical Review Letters

The existence of long range magnetic order in low dimensional magnetic systems, such as the quasi-two-dimensional (2D) van der Waals (vdW) magnets, has attracted intensive studies of new physical phenomena. The vdW FeN GeTe2 (N = 3, 4, 5; FGT) family is exceptional owing to its vast tunability of magnetic properties. In particular, a ferromagnetic ordering temperature (TC) above room temperature at N = 5 (F5GT) is observed. Here, our study shows that, by nickel (Ni) substitution of iron (Fe) in F5GT, a record high TC = 478(6) K is achieved. Importantly, pervasive, beyond-room-temperature ferromagnetism exists in almost the entire doping range of the phase diagram of Ni-F5GT. We argue that this striking observation in Ni-F5GT can be possibly due to several contributing factors, including increased 3D magnetic couplings due to the structural alterations.