Related papers: Spontaneous Magnetization of an Ideal Ferromagnet:…
We consider the spin-S ferromagnetic Heisenberg model in three dimensions, in the absence of an external field. Spin wave theory suggests that in a suitable temperature regime the system behaves effectively as a system of non-interacting…
The spontaneous magnetization is proved to vanish continuously at the critical temperature for a class of ferromagnetic Ising spin systems which includes the nearest neighbor ferromagnetic Ising spin model on $\mathbb Z^d$ in $d=3$…
We present the perturbation theory for lattice magnon fields of $D$-dimensional O(3) Heisenberg ferromagnet. The effective Hamiltonian for the lattice magnon fields is obtained starting from the effective Lagrangian, with two dominant…
In 1956 Dyson analyzed the low-energy excitations of a ferromagnet using a Hamiltonian that was non-Hermitian with respect to the standard inner product. This allowed for a facile rendering of these excitations (known as spin waves) as…
We have studied needle shaped three-dimensional classical spin systems with purely dipolar interactions in the microcanonical ensemble, using both numerical simulations and analytical approximations. We have observed spontaneous…
We study the quantum phase transition occurring in an infinite homogeneous system of spin 1/2 fermions in a non-relativistic context. As an example we consider neutrons interacting through a simple spin-spin Heisenberg force. The two…
The systematic effective Lagrangian method was first formulated in the context of the strong interaction: chiral perturbation theory (CHPT) is the effective theory of Quantum Chromodynamics (QCD). It was then pointed out that the method can…
We consider the superconducting pairing induced by spin waves exchange in a ferromagnet with both conduction and localized electrons, the latter being described as spins. We use the microscopic Eliashberg theory to describe the pairing of…
A novel method invented to measure the minute thermodynamic spin magnetization of dilute two dimensional fermions is applied to electrons in a silicon inversion layer. Interplay between the ferromagnetic interaction and disorder enhances…
We investigate ultrafast demagnetization due to electron-phonon interaction in a model band-ferromagnet. We show that the microscopic mechanism behind the spin dynamics due to electron-phonon interaction is the interplay of scattering and…
We explore the derivation of interatomic exchange interactions in ferromagnets within density-functional theory (DFT) and the mapping of DFT results onto a spin Hamiltonian. We delve into the problem of systems comprising atoms with strong…
Sr$_2$IrO$_4$ is a weak ferromagnet where the spin arrangement is canted anti-ferromagnetic (AF). Moreover, the spin-structure coupling plays and important role in magnetic behavior of Sr$_2$IrO$_4$. In this concern the magnetization under…
The role of dipolar interactions and anisotropy are important to obtain, otherwise forbidden, ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monolayers). Here we demonstrate that conventional…
The spin wave dispersion relation in both clean and disordered itinerant quantum ferromagnets is calculated. It is found that effects akin to weak-localization physics cause the frequency of the spin-waves to be a nonanalytic function of…
The low-temperature properties of systems characterized by a spontaneously broken internal rotation symmetry, O($N$) $\to$ O($N$-1), are governed by Goldstone bosons and can be derived systematically within effective Lagrangian field…
Interactions are responsible for intriguing physics, e.g. emergence of exotic ground states and excitations, in a wide range of systems. Here we theoretically demonstrate that dipole-dipole interaction leads to bosonic eigen-excitations…
Within the framework of effective Lagrangians we calculate the free energy density for an O($N$) antiferromagnet in 2+1 dimensions up to three-loop order in the perturbative expansion and derive the low-temperature series for various…
The Pauli exclusion principle combined with interactions between fermions is a basic mechanism across condensed-matter systems giving rise to a spontaneous breaking of the spin-space rotation symmetry of spin-ordered phases. Ferromagnetism…
The self-consistent spin-wave theory is applied to investigate the magnetization distribution around the impurity in isotropic and easy-axis two-dimensional ferro- and antiferromagents. The temperature dependences of host magnetization…
In the last decade it has been proven that the standard spin wave theory was able to provide accurate zero-temperature results for a number of low-dimensional Heisenberg spin systems. In this chapter we introduce the main ingredients of the…