Equilibrium current vortices in simple metals doped with rare earths (original) (raw)

The easy axis of the magnetic response of the conduction electrons of yttrium and rare earths

2003

We describe a scheme for first-principles calculations of the static, paramagnetic, spin susceptibility of metals with relativistic effects such as spin-orbit coupling included. This gives the direction for an applied modulated magnetic field to maximise its response. This easy axis depends on the modulation's wave-vector q. For h.c.p. yttrium we find the peak response at a q = (0, 0, 0.57)π/c, coincident with a Fermi surface nesting vector, to have an easy axis perpendicular to q. This is consistent with the helical anti-ferromagnetic order found in many dilute rare earth-Y alloys. Conversely, the easy axis for the response to a uniform magnetic field lies along the c-axis. The conduction electrons' role in the canting of magnetic moments in Gd − Y alloys and other rare earth materials is mooted.

Equilibrium current vortices in rare-earth-doped simple metals

2020

Adam B. Cahaya, Alejandro O. Leon, Mojtaba Rahimi Aliabad, and Gerrit E. W. Bauer 1 Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok 16424, Indonesia Departamento de F́ısica, Facultad de Ciencias Naturales, Matemática y del Medio Ambiente, Universidad Tecnológica Metropolitana, Las Palmeras 3360, Ñuñoa 780-0003, Santiago, Chile Nano-Structured Coatings Institute of Yazd Payame Noor University, P.O. Code 89431-74559, Yazd, Iran 5 WPI-AIMR & CSRN, Tohoku University, Sendai 980-8577, Japan Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan and Zernike Institute for Advanced Materials, Groningen University, The Netherlands (Dated: June 24, 2020)

Absence of the hyperfine magnetic field at the Ru site in ferromagnetic rare-earth intermetallics

Physical Review B, 2010

The Mössbauer Effect(ME) is frequently used to investigate magnetically ordered systems. One usually assumes that the magnetic order induces a hyperfine magnetic field, B hyperf ine , at the ME active site. This is the case in the ruthenates, where the temperature dependence of B hyperf ine at 99 Ru sites tracks the temperature dependence of the ferromagnetic or antiferromagnetic order. However this does not happen in the rare-earth intermetallics, GdRu 2 and HoRu 2. Specific heat, magnetization, magnetic susceptibility, Mössbauer effect, and neutron diffraction have been used to study the nature of the magnetic order in these materials. Both materials are found to order ferromagnetically at 82.3 and 15.3 K, respectively. Despite the ferromagnetic order of the rare earth moments in both systems, there is no evidence of a correspondingly large B hyperf ine in the Mössbauer spectrum at the Ru site. Instead the measured spectra consist of a narrow peak at all temperatures which points to the absence of magnetic order. To understand the surprising absence of a transferred hyperfine magnetic field, we carried out ab initio calculations which show that spin polarization is present only on the rare-earth site. The electron spin at the Ru sites is effectively unpolarized and, as a result, B hyperf ine is very small at those sites. This occurs because the 4d Ru electrons form broad conduction bands rather than localized moments. These 4d conduction bands are polarized in the region of the Fermi energy and mediate the interaction between the localized rare earth moments.

Spin Hall torques generated by rare-earth thin films

Physical Review B, 2017

We report an initial experimental survey of spin-Hall torques generated by the rare-earth metals Gd, Dy, Ho, and Lu, along with comparisons to first-principles calculations of their spin Hall conductivities. Using spin torque ferromagnetic resonance (ST-FMR) measurements and DC-biased ST-FMR, we estimate lower bounds for the spin-Hall torque ratio, ξSH, of ≈ 0.04 for Gd, ≈ 0.05 for Dy, ≈ 0.14 for Ho, and ≈ 0.014 for Lu. The variations among these elements are qualitatively consistent with results from first principles (density functional theory, DFT, in the local density approximation with a Hubbard-U correction). The DFT calculations indicate that the spin Hall conductivity is enhanced by the presence of the partially-filled f orbitals in Dy and Ho, which suggests a strategy to further strengthen the contribution of the f orbitals to the spin Hall effect by shifting the electron chemical potential.

Magnetic Excitations of Rare Earth Atoms and Clusters on Metallic Surfaces

Nano Letters, 2012

Magnetic anisotropy and magnetization dynamics of rare earth Gd atoms and dimers on Pt(111) and Cu(111) were investigated with inelastic tunneling spectroscopy. The spin excitation spectra reveal that giant magnetic anisotropies and lifetimes of the excited states of Gd are nearly independent of the supporting surfaces and the cluster size. In combination with theoretical calculations, we argue that the observed features are caused by strongly localized character of 4f electrons in Gd atoms and clusters.

Lanthanide contraction and magnetism in the heavy rare earth elements

Nature, 2007

The heavy rare earth elements crystallize into hexagonally close packed (h.c.p.) structures and share a common outer electronic configuration, differing only in the number of 4f electrons they have 1 . These chemically inert 4f electrons set up localized magnetic moments, which are coupled via an indirect exchange interaction involving the conduction electrons. This leads to the formation of a wide variety of magnetic structures, the periodicities of which are often incommensurate with the underlying crystal lattice 2 . Such incommensurate ordering is associated with a 'webbed' topology 3,4 of the momentum space surface separating the occupied and unoccupied electron states (the Fermi surface). The shape of this surface-and hence the magnetic structure-for the heavy rare earth elements is known to depend on the ratio of the interplanar spacing c and the interatomic, intraplanar spacing a of the h.c.p. lattice 5 . A theoretical understanding of this problem is, however, far from complete. Here, using gadolinium as a prototype for all the heavy rare earth elements, we generate a unified magnetic phase diagram, which unequivocally links the magnetic structures of the heavy rare earths to their lattice parameters. In addition to verifying the importance of the c/a ratio, we find that the atomic unit cell volume plays a separate, distinct role in determining the magnetic properties: we show that the trend from ferromagnetism to incommensurate ordering as atomic number increases is connected to the concomitant decrease in unit cell volume. This volume decrease occurs because of the so-called lanthanide contraction 6 , where the addition of electrons to the poorly shielding 4f orbitals leads to an increase in effective nuclear charge and, correspondingly, a decrease in ionic radii.

The role of spin-lattice coupling for ultrafast changes of the magnetic order in rare earth metals

Applied Physics Letters

By comparing femtosecond laser-pulse-induced spin dynamics in the surface state of the rare earth metals Gd and Tb, we show that the spin polarization of valence states in both materials decays with significantly different time constants of 15 ps and 400 fs, respectively. The distinct spin polarization dynamics in Gd and Tb are opposed by similar exchange splitting dynamics in the two materials. The different time scales observed in our experiment can be attributed to weak and strong 4f spin to lattice coupling in Gd and Tb, suggesting an intimate coupling of spin polarization and 4f magnetic moment. While in Gd the lattice mainly acts as a heat sink, it contributes significantly to ultrafast demagnetization of Tb. This helps explain why all optical switching is observed in FeGd-but rarely in FeTb-based compounds.

Theory of spin transfer phenomena in magnetic metals and semiconductors

Solid State Communications, 2006

We propose a general theory of the spin-transfer effects that occur when current flows through inhomogeneous magnetic systems. Our theory does not rest on an appeal to conservation of total spin, can assess whether or not current-induced magnetization precession and switching in a particular geometry will occur coherently, and can estimate the efficacy of spin-transfer when spin-orbit interactions are present. We illustrate our theory by applying it to a toy-model twodimensional-electron-gas ferromagnet with Rashba spin-orbit interactions. q

Orbital-resolved spin model for thermal magnetization switching in rare-earth-based ferrimagnets

The switching of rare-earth-based ferrimagnets triggered by thermal excitation is investigated on the basis of an atomistic spin model beyond the rigid-spin approximation, distinguishing magnetic moments due to electrons in d and f orbitals of the rare earth. It is shown that after excitation of the conduction electrons a transient ferromagneticlike state follows from a dissipationless spin dynamics where energy and angular momentum are distributed between the two sublattices. The final relaxation can then lead to a new state with the magnetization switched with respect to the initial state. The time scale of the switching event is to a large extent determined by the exchange interaction between the two sublattices.