H. Wan

Giant magnetoresistance in magnetically inhomogeneous thin films

Giant magnetoresistance (GMR) has been observed in thin films of Fe and Co in Ag. The best results were obtained in the Ag‐rich samples with a maximum value of 25% in Co20Ag80 at 30 K. The GMR values are slightly increased upon annealing. Magnetic data show a magnetic transition below room temperature which may be due to spin‐glass type of behavior. These results are consistent with the microstructure studies which showed a single face centered cubic phase, with very fine grains. Upon annealing separation of the two components is achieved with substantial grain growth.

Giant magnetoresistance studies in (Fe,Co)‐Ag films

Giant magnetoresistance (GMR) values were measured in thin films of Fe and Co in Ag. The best GMR results were observed in Ag‐rich specimens, with maxima of 25% (30 K) and 14% (20 K) observed in Co20Ag80 and Fe25Ag75, respectively. Magnetic data indicate a spin glasslike behavior in the as‐deposited Ag‐rich films. The as‐made samples have a nanostructure, with a face centered cubic structure. Annealing of the samples over the temperature range of 200 °C to 700 °C led to grain growth and subsequent phase separation of the constituent metals. A summary of the magnetic and electrical transport properties is presented, in relation to the crystal structure and microstructure of the TM‐Ag films (TM=Fe,Co).

Origin of coercivity in (Fe,Co)-based granular films

The magnetic behavior of Co and Fe granular films was studied relative to their host matrix environment (BN, SiO2). The crystal structure of Co and Fe in the as‐deposited samples is α‐Co (hcp) and α‐Fe (bcc) respectively, with particle sizes ranging between 3 and 9 nm. The coercivities measured ranged from a few tens to a few hundreds Oe, with the higher values observed for particles embedded in the oxygen based matrix.

Microstructure and magnetic hysteresis of CoCu films

Abstract CoCu films were prepared by dc magnetron sputtering over a wide range of compositions. The as-made films showed a cluster glass-type behavior with unsaturated hysteresis loops. Detectable phase decomposition was achieved by isothermal annealing at temperatures ranging between 250 and 850°C. Higher coercivities were obtained in the annealed samples with values of the order of 500 Oe. The films also showed giant magnetoresistance (GMR) with a maximum value of 13% observed in the 17 at% Co samples at 30 K.

Giant magnetoresistance studies in (Co,Fe)Ag films

Abstract Giant magnetoresistance (GMR) has been observed in thin films of Co and Fe in Ag. The best results were obtained in the Ag-rich samples with a maximum value of 25% in Co20Ag80 at 30K. The GMR values are slightly increased upon annealing. Magnetic data show a magnetic transition below room temperature characteristic of a spin-glass or superparamagnetic behavior. Microstructure studies with conventional TEM showed a single face centered cubic phase, consisting of veryfine grains with sizes below 100A. Upon annealing, separation of the two components is achieved with substantial grain growth.

Thickness dependence of coercivity in Co‐Ni thin films

The magnetic properties and microstructure of sputtered Co80Ni20 thin films with a thickness in the range of 400–3800 A have been studied using SQUID magnetometry, x‐ray diffraction and transmission electron microscopy (TEM). Both the electron and x‐ray diffraction results show that all the films have an hcp structure. As the film thickness decreases the grain size decreases and the c axis is inclined to the film plane. The intrinsic coercivity decreases as the thickness increases when the applied field is parallel to the film plane. The dependence of coercivity on the angle θ between the field direction and the normal to the film plane indicates that the coercivity is due to domain wall pinning. The domain wall structure and pinning force play a major role in the thickness dependence of coercivity for films with thickness D<1000 A.

Magnetic properties of amorphous Dy-Co films with different thickness

Abstract The thickness dependence of magnetic properties has been studied in amorphous Dy x Co 1- x thin films ( x =0.43, 0.49). The compensation temperature and coercivity were found to be thickness dependent. In uncoated films with thickness below 800 A, the coercivity and compensation temperature were found to decrease with thickness and this was attributed to the oxidation of the surface layer of the films. This behavior was not observed in the thicker films and in SiO-coated films. In these films, both the compensation temperature and coercivity do not change with thickness and they depend only on the intrinsic properties.

Magnetic properties of Er-Ta granular thin films

Abstract The magnetic and structural properties of granular Er-Ta films have been studied with SQUID magnetometry and transmission electron microscopy (TEM). The films have been fabricated by co-sputtering using DC magnetron sputtering. The particle size of granular films was found to be affected by both the composition and annealing temperature. Electron diffraction patterns showed that the as-sputtered Er-Ta films have an amorphous structure. After annealing at different temperatures, the amorphous phase transforms first into an intermediate fcc structure and finally into an Er hcp phase and Ta phase, in which granular particles are clearly observed by TEM. The intermediate fcc structure shows only one magnetic transition whereas the hcp Er granular solids show a superparamagnetic and a modulated magnetic phase transitions. The modulated phase is not as obvious as in hcp Er films and this may be due to finite size effects.

Magnetic hardening in melt‐spun Fe‐rich Fe‐Mo alloys

The change in magnetic properties corresponding to the structural changes that occur during aging at temperatures in the range 500–900 °C have been studied in melt‐spun Fe‐Mo alloys using magnetometry, x‐ray diffraction (XRD), and transmission electron microscopy (TEM). The as‐spun ribbons were found to be magnetically soft with a coercivity smaller than 180 Oe. After a heat treatment at temperatures in the range of 600–670 °C, the coercivity was found to increase to 600 Oe and the magnetization decreased. It is suggested that Mo clustering takes place with heat treatment and this may explain the decreased magnetization and increased coercivity of the samples. Mo‐rich clusters can act as domain‐wall pinning centers and therefore can lead to an increased coercivity.

Microstructure And Giant Magnetoresistance In (Co, Fe)/Ag Films

Giant magnetoresistance values are observed in Co/Ag composite films. The largest change in magnetoresistance values is measured in the as-deposited Ag-rich samples with maxima on the order of 30%, at 30 K. X-ray diffraction and electron microscope studies indicate a uniform FCC structure with an apparent composition dependent lattice parameter. High resolution electron micrographs provide the first evidence of Co clustering in an Ag matrix via the observation of the lattice spacing which clearly corresponds to the [200] line of FCC Co. It is believed that the GMR is due to interfacial scattering from these clusters. >