High magnetic field properties and ESR of the compounds

compounds have a layered structure made of alternating Ni-O and Li-O slabs. An amount z of extra divalent Ni ions is always present in the Li-O layers. We show, using high field magnetisation, static and dynamic susceptibility and high frequency ESR, that the magnetic properties are driven by the z parameter. The compounds can be described as ferromagnetic Ni-O layers, bridged by clusters possessing a net ferromagnetic moment. Received: 24 July 1998 / Revised and Accepted: 23 September 1998     

Synthesis,Structure and Magnetic Properties of a Cyano‐bridged Dinuclear Compound fac‐{[FeIII(pzTp)(CN)2(μ‐CN)] CuII(TPyA)}·Et2O·ClO4 (pzTp = tetrakis(pyrazolyl)borate)

The reaction of tricyanometallate precursor, (Bu₄N)[(pzTp)Fe(CN)₃] with Cu(ClO₄)₂·6H₂O in the presence of the tetradentate ligand tris(2‐pyridylmethyl)amine (TPyA) afford the dinuclear compound fac‐{[Fe^III(pzTp)(CN)₂(μ‐CN)]Cu^II(TPA)}·Et₂O·ClO₄ ( 1 ) (pzTp = tetrakis(pyrazolyl)borate). The molecular structure was determined by single‐crystal X‐ray diffraction. In compound 1 , the Fe^III ion is coordinated by three cyanide carbon atoms and three nitrogen atoms of pzTp anions. Whereas, the Cu^II ion is surrounded by one cyanide nitrogen atom and four nitrogen atoms from the TPyA ligand. Magnetic measurements indicate the intramolecular ferromagnetic coupling is observed for compound 1 , and it has S = 1 ground states.     

Ferromagnetic resonance investigation of nanocrystalline FeCuNbSiB

An elaborate line-shape analysis of the ferromagnetic resonance (FMR) spectra taken in the temperature range 100 K to 350 K on amorphous FeCuNbSiB alloys before and after nanocrystallizing them reveals that in the nanocrystalline state, (i) spin wave stiffness (D) is enhanced while the saturation magnetization,M _S, is reduced, (ii) both the ‘in-plane’ anisotropy field,H _K, as well as the FMR line-width scale with MS, (iii) the single-ion anisotropy of spin-orbit plus crystal field origin dominates over the twoion anisotropy of dipolar origin and (iv) multi-magnon scattering contributions to FMR line-width become important in some cases     

Electronic structure of Ga1−xCrxN investigated by photoemission spectroscopy

We have obtained the Cr 3d-like energy states, which located in the band gap of GaN by means of resonant photoemission spectroscopy. In the difference spectrum between the valence band photoemission spectra of non-doped GaN and that of the Ga_0.937Cr_0.063N, we observed the new energy state, in band gap, consists of Cr 3d-like and N 2p-like component by strong hybridization.     

Ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies

We develop a model for ferromagnetic resonance in systems with competing uniaxial and cubic anisotropies. This model applies to (i) magnetic materials with both uniaxial and cubic anisotropies, and (ii) magnetic nanoparticles with effective core and surface anisotropies; We numerically compute the resonance frequency as a function of the field and the resonance field as a function of the direction of the applied field for an arbitrary ratio of cubic-to-uniaxial anisotropy. We also provide some approximate analytical expressions in the case of weak cubic anisotropy. We propose a method that uses these expressions for estimating the uniaxial and cubic anisotropy constants, and for determining the relative orientation of the cubic anisotropy axes with respect to the crystal principle axes. This method is applicable to the analysis of experimental data of resonance type measurements for which we give a worked example of an iron thin film with mixed anisotropy.     

Aspects of “low field” magnetotransport in epitaxial thin films of the ferromagnetic metallic oxide SrRuO3

Epitaxial thin films of the conductive ferromagnetic oxide SrRuO₃ were grown on an (0 0 1) SrTiO₃ (STO) substrate by using DC sputtering technique. The magnetic and magnetoresistive properties of the films were measured by applying the magnetic field both perpendicular (out-of-plane) and parallel (in-plane) to the film plane and ever maintaining the direction of the applied field perpendicular to that of the transport current. The films grown on an (0 0 1) STO substrate showed identical magnetization properties in two orthogonal crystallographic directions of the substrate, [1 0 0]_S and [0 0 1]_S (in-plane and out-of-plane geometry), which suggests the presence of a multi domain structure within the plane of the film. For such samples, no anisotropic field (hard axis) along de [0 0 1]s direction, i.e., perpendicular to the film-plane could be detected. Nevertheless, a distinguishable temperature dependent out-of-plane anisotropic magnetoresistance (MR) along with strong temperature dependent low field hysteretic MR(H) behavior was detected for the studied films. A negative MR ratio MR(T)=[ρ(μ₀H=9 T; T)−ρ( μ₀H=0 T; T)]/ρ( μ₀H=0 T; T) on the order of a few percent, with maximums of 6% and 4% (right at the Curie temperature, T_C 160 K) was calculated for an in-plane and out-of plane measuring geometry, respectively. In addition there is an equally strong MR effect at low temperatures, which might be related to the temperature dependence of the magnetocrystalline anisotropy together with a magnetization rotation. Both the MR(T) behavior and the achieved values (except for T<30 K) are similar to those obtained on SrRuO₃ films grown on 2° miscut (0 0 1) STO substrates with the current parallel to the field and parallel to the direction, which was identified as the easier axis for magnetization.     

Characterization of a ferromagnetic porous silicon-based Ni/Si nanocomposite with a novel strong high-field anisotropy

Ferromagnetic (Ni) filaments are embedded into a porous silicon template by an electrochemical deposition process. During cathodic deposition using NiCl₂ as electrolyte the channels of the meso-/macroporous silicon structure are filled with metallic Ni. The resulting nanocomposite system consists of silicon as base material as well as of implemented Ni-structures, especially of highly oriented Ni-wires perpendicular to the surface showing an exceptionally high aspect ratio (>300) and is of interest for applications in microtechnology. The length of the Ni-wires is in the range of a few tens of micrometers. Concomitant with the growth of wires, spheres or ellipsoidally shaped particles are formed during the Ni-filling procedure, whose spatial frequency and distribution become tunable. Structural investigations of this system, using SEM and EDX as well as investigations of the magnetic behaviour using SQUID-magnetometry, demonstrate the dependency of the magnetic properties on the filling status of the samples. The hysteresis loops in the low-field regime up to 500 Oe as well as magnetization curves in the high-field range of a few tesla display a strong magnetic anisotropy due to magnetic rearrangements. At fields around 5 T, a decline of the magnetization followed by a steep increase is observed. This magnetic field-induced anisotropy depends on the detailed growth of the Ni within the pores which can be controlled by the deposition process. It is governed by yet unknown antiferromagnetic exchange between the wires, and inherently connected with the shape of the magnetic nano-objects.     

Layer-resolved optical conductivity of Co | Pt multilayers

The complex optical conductivity tensor is calculated for the Co | Pt multilayer systems by applying a contour integration technique within the framework of the spin-polarized relativistic screened Korringa–Kohn–Rostoker method. It is shown that the optical conductivity of the Co | Pt multilayer systems is dominated by contributions arising from the Pt cap and/or substrate layers.     

Phase separation effects in charge-ordered Pr<Subscript>0.5</Subscript>Ca<Subscript>0.5</Subscript>MnO<Subscript>3</Subscript> thin film

Compressed Pr_0.5Ca_0.5MnO₃ films (250 nm) deposited on LaAlO₃ have been studied by Electron Spin Resonance technique under high frequency and high magnetic field. We show evidences for the presence of a ferromagnetic phase (FM) embedded in the charge-order phase (CO), in form of thin layers which size depends on the strength and orientation of the magnetic field (parallel or perpendicular to the substrate plane). This FM phase presents an easy plane magnetic anisotropy with an anisotropy constant 100 times bigger than typical bulk values. When the magnetic field is applied perpendicular to the substrate plane, the FM phase is strongly coupled to the CO phase whereas for the parallel orientation it keeps an independent ferromagnetic resonance even when the CO phase becomes antiferromagnetic.     

On dissipation mechanisms in micromagnetics

Within the framework of a dynamic version of micromagnetics [1,2], the space-time evolution of magnetization in a rigid, saturated ferromagnet is governed by the following equation: γ^-1 = ×( + + div ), where the interaction couple × and the couple stress are to be constitutively specified. Under constitutive assumptions for , , and the free energy ψ, that allow for equilibrium response and viscosity out of equilibrium and agree with the dissipation principle - ^. + ^. ∇ - ≥ 0, the above evolution equation yields a broad generalization of the standard Gilbert equation. In particular, while the standard Gilbert equation only incorporates relativistic dissipation, it is shown that the dissipation mechanisms compatible with the generalized Gilbert equation include exchange dissipation [2], dry-friction dissipation [3], and others. It is also shown that the additional term proposed in [4] to account for exchange dissipation, rather than having a genuine dissipative nature, modifies instead the nature of possible equilibria; and that such a modification is an automatic side effect when dry-friction dissipation is incorporated in the manner of [3]. Received 31 October 2000