Lu Mu

Magnetic Properties and Intergranular Action in Bonded Hybrid Magnets

Abstract Magnetic properties and intergranular action in bonded hybrid magnets, based on NdFeB and strontium ferrite powders were investigated. The long-range magnetostatic interaction and short-range exchange coupling interaction existed simultaneously in bonded hybrid magnets, and neither of them could be neglected. Some magnetic property parameters of hybrid magnets could be approximately obtained by adding the hysteresis loops of two magnets pro rata.

Spin Wave Resonance in Fe/Cu Compositionally Modulated Films

Fe/Cu compositionally modulated films made by rf sputtering were investigated with ferromagnetic resonance. Spin wave resonances related to interlayer exchange coupling were observed and the phase change of the spin wave was shared by both the Fe and Cu sublayers. The effective spin wave dispersion coefficient was found to increase with increasing thickness of Cu sublayers.

Magneto-Optical Kerr Effect of Compositionally Modulated Co/Pt Films

In this paper the magneto-optical polar Kerr rotation spectra of compositionally modulated films (CMF) Co/Pt are calculated by using Fresnels equations. For CMF Co/Pt with dCo/dPt=1/2, 1 and 2 the magneto-optical Kerr rotation at any wavelength increases with the increasing modulation wavelength in the wavelength region from 200 to 800 nm. For CMF Co/Pt of constant dPt the Kerr rotation increases with dCo increasing while of constant dCo the Kerr rotation increases with dPt decreasing. From numerical calculations it is suggested that for CMF Co/Pt with small dPt the Pt sublayer is polarized and has a positive contribution to the Kerr rotation of CMF Co/Pt.

Enhancement of Kerr rotation of thin Fe films

The magneto-optical Kerr rotation spectra in the region 400-700nm is studied for single layer Fe films. Experimental and theoretical calculation show that in the whole measurement wavelength range an enhancement of Kerr rotation occurs when the thickness of Fe is smaller than about 150A. The thickness dependence of Kerr rotation of single layer Fe and Fe/Cu bilayer is compared. It is concluded that the Kerr rotation is dependent sensitively on the optical constants of underlying materials and the thickness of magnetic layer.

Model of hybrid interfacial domain wall in ferromagnetic/antiferromagnetic bilayers*

A general model of a hybrid interfacial domain wall (HIDW) in ferromagnetic/antiferromagnetic exchange biased bilayers is proposed, where an interfacial domain wall is allowed to extend into either the ferromagnetic or antiferromagnetic layer or across both. The proposition is based on our theoretical investigation on thickness and field dependences of ferromagnetic domain wall (FMDW) and antiferromagnetic domain wall (AFDW), respectively. Good match of the simulation to the hysteresis loops of a series of NiFe/FeMn exchange-biased bilayers confirms the existence of the HIDW, where the AFDW part is found to preferentially occupy the entire antiferromagnetic layer while the FMDW shrinks with the increased magnetic field as expected. The observed asymmetry between the ascending and descending branches of the hysteresis loop is explained naturally as a consequence of different partition ratios between AFDW and FMDW.

A RKKY Model Fitting of Nuclear Magnetic Resonance Spectra of 63Cu in Fe/Cu Multilayers

In this letter, a theoretical fit of nuclear magnetic resonance spectra of 63Cu in Cu layers of Fe/Cu Multilayers is given based on RKKY theory. The values of exchange field and additional Knight shift are fitted, which agree approximately with the experimental data.

Structure and Magnetic Properties of Sputtered Bi2DyFe5O12 Films

The effects of the annealing temperature and time on the structure and magnetic properties of the sputtered BiDy-iron garnet films were investigated. X-ray diffraction analysis shows that the as-sputtered films are amorphous. After annealing at about 550°C, amorphous films crystallize into the garnet phase and an unknown phase. The intensity of the unknown phase decreases with increasing annealing temperature and time and vanishes at 650°C for 30 min. It is found that the unknown phase has a large influence on the half-width of the (420) x-ray diffraction peak. The as-sputtered films have a very small magnetization of about 1 emu/g at room temperature. When films are annealed above 570°C, the magnetization increases rapidly with increasing annealing temperature and time.

Giant Magnetoresistance in Granular Type (Co-Ag)/Ag Multilayers

The dependence of giant magnetoresistance of sputtered granular type (Co-Ag)/Ag multilayers on the thickness of Ag layers and magnetic layers with varying Co content in the magnetic layers was studied. The magnetoresistance ratio ΔR/R was found to be enhanced by 2-7 times comparing with the single layer granular films. The enhancement was explained by the antiferromagnetic coupling due to magnetostatic interaction between the Co clusters in neighboring magnetic layers.

Memory Effect in Ceramic Superconductors

We measured the time decay of the magnetic moment of high Tc superconductors YBa2Cu3O7-δ ceramic samples and found the memory effect which has hitherto been reported only in single crystals. The temperature and field ranges, especially the memory time are different from those of the latter. We believed that the memory phenomenon in ceramic samples at liquid nitrogen temperature can only be understood in a combined picture of both flux creep and glass behaviour.

Magneto-optical Kerr Effect of NdFe Films and NdFe/Cu(Al) Bilayers

In this paper single layer NdFe film, bilayer NdFe/Cu and NdFe/Al films made by vacuum evaporation were studied. The magneto-optical Kerr effect (MOKE) and reflectivity spectra were measured. The following results were found: the contribution of Nd to MOKE is mainly at short wavelengths, for NdFe/Al the MOKE enhancement locates in the short wavelength range and for NdFe/Cu the enhancement peak locates near the absorption edge of reflector Cu, and in the MOKE spectra of bilayer NdFe/Cu film with some compositions, sign reversals were observed.