Magnetocaloric effect in random magnetic anisotropy materials

In this letter we report the results of entropy variations in random anisotropy magnets composed of TbxY1−xAl2, with x=0.15, 0.20, 0.25, 0.35, 0.40, and 0.50. We discovered large entropy variation associated with the spin glass to paramagnetictransition. Both temperature transition and entropy changes were studied at different temperatures and with different compositions. Our conclusion is that these materials are suitable candidates for use as magnetic refrigerants in a temperature range below 40 K

Muon spin rotation and neutron scattering study of the non-centrosymmetric tetragonal compound CeAuAl3

We have investigated the non-centrosymmetric tetragonal heavy-fermion compound CeAuAl3 using muon spin rotation (muSR), neutron diffraction (ND) and inelastic neutron scattering (INS) measurements. We have also revisited the magnetic, transport and thermal properties. The magnetic susceptibility reveals an antiferromagnetic transition at 1.1 K with a possibility of another magnetic transition near 0.18 K. The heat capacity shows a sharp lambda-type anomaly at 1.1 K in zero-filed, which broadens and moves to higher temperature in applied magnetic field. Our zero-field muSR and ND measurements confirm the existence of a long-range magnetic ground state below 1.2 K. Further the ND study reveals an incommensurate magnetic ordering with a magnetic propagation vector k = (0, 0, 0.52) and a spiral structure of Ce moments coupled ferromagnetically within the ab-plane. Our INS study reveals the presence of two well-defined crystal electric field (CEF) excitations at 5.1 meV and 24.6 meV in the paramagnetic phase of CeAuAl3 which can be explained on the basis of the CEF theory. Furthermore, low energy quasi-elastic excitations show a Gaussian line shape below 30 K compared to a Lorentzian line shape above 30 K, indicating a slowdown of spin fluctuation below 30 K. We have estimated a Kondo temperature of TK=3.5 K from the quasi-elastic linewidth, which is in good agreement with that estimated from the heat capacity. This study also indicates the absence of any CEF-phonon coupling unlike that observed in isostructural CeCuAl3. The CEF parameters, energy level scheme and their wave functions obtained from the analysis of INS data explain satisfactorily the single crystal susceptibility in the presence of two-ion anisotropic exchange interaction in CeAuAl3.Comment: 28 pages and 17 figure

Structure and magnetism of Tm atoms and monolayers on W(110)

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).We investigated the growth and magnetic properties of Tm atoms and monolayers deposited on a W(110) surface using scanning tunneling microscopy and x-ray magnetic circular and linear dichroism. The equilibrium structure of Tm monolayer films is found to be a strongly distorted hexagonal lattice with a Moiré pattern due to the overlap with the rectangular W(110) substrate. Monolayer as well as isolated Tm adatoms on W present a trivalent ground-state electronic configuration, contrary to divalent gas phase Tm and weakly coordinated atoms in quench-condensed Tm films. Ligand field multiplet simulations of the x-ray absorption spectra further show that Tm has a |J=6,Jz=±5¿ electronic ground state separated by a few meV from the next lowest substates |J=6,Jz=±4¿ and |J=6,Jz=±6¿. Accordingly, both the Tm atoms and monolayer films exhibit large spin and orbital moments with out-of-plane uniaxial magnetic anisotropy. X-ray magnetic dichroism measurements as a function of temperature show that the Tm monolayers develop antiferromagnetic correlations at about 50 K. The triangular structure of the Tm lattice suggests the presence of significant magnetic frustration in this system, which may lead to either a noncollinear staggered spin structure or intrinsic disorder.This work was supported by the European Research Council (StG 203239 NOMAD), Agència de Gestió d’Ajuts Universitaris i de Recerca (2009 SGR 695), Spanish MINECO (Grants No. MAT2009-10040, No. MAT2010-15659, and No. MAT2012-31309), Gobierno de Aragón (Grant No. E81), Fondo Social Europeo, and the Swiss Competence Centre for Materials Science and Technology (CCMX).Peer Reviewe

Subatomic movements of a domain wall in the Peierls potential

Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice periodicity. Domain walls are found to be weakly mobile within valleys of the atomic washboard but become unexpectedly flexible on Peierls ridges, where they can be kept in a bi-stable state by ac magnetic field. We describe the latter observation in terms of a single magnetic kink propagating along a domain wall

MAGNETIC PROPERTIES OF DILUTE RANDOM MAGNETIC ANISOTROPY SYSTEMS (DyxY1-x) Al2

The magnetic phase diagram for the RMA system DyxY1-xAl2 is determined. For x ≤ 0.30 a PM/SG transition is found, while for x > 0.30 a CSG phase exists. No long range magnetic order appears, yet the initial susceptibility diverges at and below the PM/CSG transition. Scaling analysis indicates phase transitions, and the critical exponents β, γ, δ, δ1 and ϕ and βs, γs and δs have been determined

Strain-induced magnetization reorientation in epitaxial Cu/Ni/Cu rings

The role of the strain state in epitaxial (001)-oriented Cu/Ni(14 nm)/Cu rings is investigated using a combination of magnetic force microscopy and finite-element calculations. Rings with an external diameter of 3 and 2 μm and linewidth W larger than 400 nm show two different structures: domains with magnetization oriented in the radial direction exist at the inner and outer radius, separated by an area in the interior of the ring consisting of stripe domains with perpendicular magnetization. The former is the sole magnetic structure observed for W < 400 nm. Micromagnetic calculations on narrow-linewidth structures indicate that the radial domain-wall structure consists of elliptical Bloch lines with a shorter and longer length along the tangential and radial directions, respectively. Finite-element calculations show that the anisotropic relaxation of the in-plane strain is larger at the ring inner and outer edges than in the interior part of the ring and accounts for the reorientation of the magnetization direction.Singapore-MIT AllianceNational Science Foundation (U.S.

Strain-induced magnetization reorientation in epitaxial Cu/Ni/Cu rings

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- Trabajo presentado como al Joint European Magnetic Symposia (JEMS2012).The role of the strain state in epitaxial (001)-oriented Cu/Ni(14 nm)/Cu rings is investigated using a combination of magnetic force microscopy and finite-element calculations. Rings with an external diameter of 3 and 2 ¿m and linewidth W larger than 400 nm show two different structures: domains with magnetization oriented in the radial direction exist at the inner and outer radius, separated by an area in the interior of the ring consisting of stripe domains with perpendicular magnetization. The former is the sole magnetic structure observed for W<400 nm. Micromagnetic calculations on narrow-linewidth structures indicate that the radial domain-wall structure consists of elliptical Bloch lines with a shorter and longer length along the tangential and radial directions, respectively. Finite-element calculations show that the anisotropic relaxation of the in-plane strain is larger at the ring inner and outer edges than in the interior part of the ring and accounts for the reorientation of the magnetization direction.This work has been supported by Spanish MICINN (Grants No. MAT2009-10040) and Gobierno de Aragón (Grants No. E81 and PI049/08) and Fondo Social Europeo, the Singapore-MIT Alliance and National Science Foundation.Peer Reviewe

MAGNETIC ANISOTROPY OF TERNARY (TbxGd1-x) Al2 COMPOUNDS

Magnetization measurements, parallel and perpendicular to the magnetic field have been performed on crystals of TbxGd1-xAl2. We determine the crystal field parameters by fitting the field and temperature dependences of the magnetization angle with [001]. The B4 and B6 CEF parameters are almost x independent, and B4 ? 5 x 10-4 K/ion for TbAl2