Low temperature magnetic properties of NdCu2

μSR experiments on NdCu₂ give evidence for short range order below 25\ K above T_N=6.5\ K. No signal was detected between 16\ K and 1.2\ K where neutron scattering reveals an incommensurate spin structure. Below 1.2\ K the μSR signal is recovered and shows a rotation with 22 MHz. This is interpreted with a squaring up of Nd spins accompanied by a decrease of magnon excitations which is reflected in a decrease of damping of the muon signal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Low temperature magnetic properties of trimeric clusters

The degeneracy in the Heisenberg model of the three chromium clusters having D₃ symmetry is split by the antisymmetric exchange interaction. Based on this new energy level scheme, the low temperature behavior of the specific heat and magnetic susceptibility are reexamined.     

Room temperature magnetic properties of ZnO nanostructured films

The ZnO nanorod array films have been epitaxially deposited on indium tin oxide (ITO) glass along 〈0001〉 direction. It is found that the film is grown in a two-step process including nanoparticle film nucleation and oriented rod growth. The as-prepared ZnO film shows a dominant diamagnetic signal and a weak ferromagnetic signal at room temperature. The room temperature ferromagnetism deteriorated by annealing in air or N₂. The photoluminescent spectra revealed that the intensity of ZnO defect band decreases after annealing. Thus, the decreased ferromagnetism is likely to have resulted from the decrease of oxygen vacancies and defects in the as-prepared film. Moreover, ZnO deposited at various times showed that defects located at or near the interface between the substrate and the film play a major role in ferromagnetism. It suggests that ferromagnetism can be tuned by changing the defects in ZnO.     

Low temperature magnetic properties of Ti-rich Fe-Ti spinels

Low temperature hysteresis loops have been measured on compositions of the spinel series Fe_3-xTi_xO₄, 0?x?1, with x=0.4, 0.5, 0.6 and 0.8. All compounds studied exhibit an anomaly of the hysteresis parameters in the temperature range 40–80 K below which a marked effect of field cooling on the hysteresis loops is observed.     

Low temperature ferromagnetic properties of CdS and CdTe thin films

The magnetic property in a material is induced by the unpaired electrons. This can occur due to defect states which can enhance the magnetic moment and the spin polarization. In this report, CdS and CdTe thin films are grown on FTO glass substrates by chemical bath deposition and close-spaced sublimation, respectively. The magnetic properties, which are introduced from oxygen states, are found in CdS and CdTe thin films. From the hysteresis loop of magnetic moment it is revealed that CdS and CdTe thin films have different kinds of magnetic moments at different temperatures. The M–H curves indicate that from 100 K to 350 K, CdS and CdTe thin films show paramagnetism and diamagnetism, respectively.A superparamagnetic or a weakly ferromagnetic response is found at 5 K. It is also observed from ZFC/FC curves that magnetic moments decrease with temperature increasing. Spin polarized density functional calculation for spin magnetic moment is also carried out.     

Low temperature magnetic and electrical properties of DHCP Ce-La alloys

Electrical resistivity and magnetic susceptibility measurements on CeLa alloys have shown that 5% La in βCe (dhcp) stabilizes βCe with respect to αCe, preventing β from transforming to α in the 15–50 K region. The remarkable Kondo-like properties of pure βCe are also found in the alloys over a wide concentration range.     

Low temperature ultrasonic properties of vapour condensed films of argon-xenon mixtures

Using surface acoustic waves we have studied the elastic properties of thin solid films of pure Argon and Xenon and of Ar–Xe mixtures condensed at 4.4 K. From our results we conclude that in all samples low energy excitations are present. They give rise to a relaxation absorption and to related changes of the sound velocity. An important difference to conventional glasses is, that even below Helium temperatures relaxation occurs not only via tunneling but also via thermally activated processes. The density of states of the low energy excitations is comparable to that of vitreous silica and increases continually with Xenon concentration.     

Room temperature magnetic properties of Fe and C implanted ZnO films

ZnO films prepared by radio frequency magnetron sputtering were singly or sequentially implanted with 120 keV Fe ions at a fluence of 5 × 10¹⁶ ions/cm² and 20 keV C ions at a fluence of 3 × 10¹⁵ ions/cm². Magnetic and optical properties as well as structures of the films have been investigated using various techniques. Magnetic measurements show that the as-deposited ZnO film presents room temperature ferromagnetism. Single Fe or C ion implantation has no contribution to enhancement in the film magnetism, while magnetic moment increases distinctly in the Fe and C ions sequentially implanted film. Results from structural measurements reveal that Fe nanoparticles are formed in the Fe singly implanted ZnO film. The post C implantation induces dissolution of Fe nanoparticles and promotes Fe atoms to substitute Zn atoms in the lattice. Based on the structural results, the effect of magnetic enhancement has been tentatively interpreted.     

Low temperature thermal—and magnetic properties of CeP and CeAs

CeP and CeAs are characterized by low temperature measurements of the specific heat, the thermal expansion, the electrical resistivity and the magnetization of single crystal specimens. These physical properties are found to be very sensitive to crystal perfection and chemical composition in both the paramagnetic and the magnetically ordered state. In the intrinsically antiferromagnetic CeP, imperfections can give rise to a remanent magnetization belowT _N .     

Low temperature studies on magnetic properties of Tm2O3

Magnetic properties of Tm₂O₃ were studied by means of magnetometry as well as by heat capacity measurements. The specific heat data were collected down to 0.35 K, and yielded some new information about crystal field splitting of the ³H₆ thulium multiplet. Some anomalous behaviour of the specific heat below 5 K was observed. It turned out, that this anomaly can be nicely described by Schottky contribution originating from crystal field levels distribution of the Tm³⁺ multiplet. No magnetic ordering was evidenced down to the lowest temperatures studied.     

Low temperature magnetic structure of MnSe

In this paper we report low temperature neutron diffraction studies on MnSe in order to understand the anomalous behaviour of their magnetic and transport properties. Our study indicates that at low temperatures MnSe has two coexisting crystal structures, high temperature NaCl and hexagonal NiAs. NiAs phase appears below 266 K and is antiferromagnetically ordered at all temperatures while the NaCl phase orders antiferromagnetically at 130 K.     

Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic,ferrite and granular thin films.Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies.GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated.It is found that several hundreds of permeability at the GHz frequency was achieved for Co100-xZrx and Co90Nb10 metallic thin films because of their high saturation magneti...     

Low temperature magnetoresistance of Al-doped ZnO films

The magnetoresistances of aluminum-doped zinc oxide thin films with thickness of 463.63, 203.03, and 66.85 nm were measured at low temperatures from 2.5 to 30 K. It is found that the samples exhibit negative magnetoresistance at all measuring temperatures. However, neither the three-dimensional nor the two-dimensional weak-localization theories can reproduce the behavior of the magnetoresistance. We find that the magnetoresistance of the three films can be well described by a semiempirical expression that takes into account the third order s-d exchange Hamiltonians describing a negative part and a two-band model for the positive contribution. This strongly suggests that the negative magnetoresistance in ZnO:Al film originates from the scattering of conduction electrons due to localized magnetic moments.     

Microwave magnetic properties of gadolinium-iron films

We have made ferromagnetic resonance measurements on Gd_1-xFe_x films, where x = 0 to 1. The saturation magnetization, g-value, the exchange stiffness constant, the magnetic damping parameter and some surface anisotropy parameters were determined. We find that the exchange decreases rapidly as the Fe content decreases. The g-values obey the Wangsness relation except near compensation. The exchange-conductivity linewidth broadening is minimal in this system.     

The critical properties of magnetic films

Within the framework of the transverse Ising model and by using the effective field theory with a probability distribution technique that accounts for the self spin correlations, we have studied the critical properties of an L-layer film of simple cubic symmetry in which the exchanges strength are assumed to be different from the bulk values in N_S surface layers. We derive and illustrate the expressions for the phase diagrams, order parameter profiles and susceptibility. In such films, the critical temperature can shift to either lower or higher temperature compared with the corresponding bulk value. We calculate also some magnetic properties of the film, such as the layer magnetizations, their averages and their profiles and the longitudinal susceptibility of the film. The film longitudinal susceptibility still diverges at the film critical temperature as does the bulk longitudinal susceptibility.     

Evolution of magnetic and microstructural properties of thick sputtered NdFeB films with processing temperature

Ta (100 nm)/NdFeB (5 μm)/Ta (100 nm) films have been deposited onto Si substrates using triode sputtering (deposition rate ∼18 μm/h). A 2-step procedure was used: deposition at temperatures up to 400 °C followed by ex-situ annealing at higher temperatures. Post-deposition annealing temperatures above 650 °C are needed to develop high values of coercivity. The duration of the annealing time is more critical in anisotropic samples deposited onto heated substrates than in isotropic samples deposited at lower temperatures. For a given set of annealing conditions (750 °C/10′), high heating rates (?2000 °C/h) favour high coercivity in both isotropic and anisotropic films. The shape and size of Nd₂Fe₁₄B grains depend strongly on the heating rate.     

Room temperature single-step electrosynthesized copper ferrite thin films and study of their magnetic properties

A single-step electrosynthesis of copper ferrite thin films from aqueous bath (which avoids anodization step for an incorporation of oxygen species into deposit) has been carried out at room temperature. Observed tetrahedral structured nanocrystalline copper ferrite thin films showed smooth, uniform and compact surface morphology. After annealing, increase in dielectric constant and reduced dielectric loss were observed. The saturation magnetization for annealed films was 292 emu/cm³ comparable to that of other reported ferrites.     

Low field magnetic properties of us

The broad peak and jumps that occur in the isofield magnetization curves of US single crystals when these are heated after first being thermally demagnetized by cooling from above T_c to low temperatures, are investigated. The jumps (two for the [110] direction, one for the [111] direction and none for the [001] direction) are correlated with the same behaviour in the initial magnetization curves and interpreted as due to the nucleation and growth of 70, 109 and 180° domains. The crystals also exhibit a high coercivity (～ 1000 Oe) and remanent magnetization of up to 92% along the [001] direction at 4 K. This enabled us to study the peak and step behaviour also by premagnetization experiments.     

Low temperature ion beam irradiation of gallium films

Ga-films in the amorphous, the -Ga, and the -Ga phase have been irradiated at low temperatures with Ar-ions and He-ions at energies 275 keV and 200 keV, respectively. The -phase can be transformed into the amorphous state by Ar-ion irradiation but not by He-ion irradiation. Rather small Ar-fluences <10¹⁴ ions/cm² are sufficient. The -phase is stable with respect to irradiation with Ar- and He-ions at small fluences. The as-quench condensed amorphous phase is stable with respect to Ar-ion irradiation, however, it transforms into the -phase at He-ion irradiation. The different short range order of the - and -phase is thought to be responsible for the different behavior at ion irradiation.This work is dedicated to Professor Dr. S. Methfessel on the occasion of his 60th birthday