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As revealed by the observation of memory effects and domain imaging, the antiferromagnetic (AFM) spin structure in exchange bias is not static. During reversal, the AFM spins form an exchange spring connected with the ferromagnet (FM). We have observed hybrid domain walls consisting of FM and AFM sections and their evolution using the magnetooptical indicator film technique. The external magnetic field moves only the FM section of the hybrid domain walls, leading to the formation of an exchange spring parallel to the interface. The nucleation and unwinding of the exchange spring occur at different locations, and the propagation depends strongly on the chirality of the FM domain walls. Index Terms--Antiferromagnetic (AFM), domain, exchange bias, spin structure.

The magnetic and optical characteristics of gamma-Fe2O3 nanocrystals synthesized in a polymer matrix by ion exchange and precipitation reaction were investigated. The results showed that the optical absorption spectrum of the sample was red-shifted, in contrast with superconductor nanocrystals where a blue shift from the corresponding bulk sample was observed. It was proposed that the lattice strain in the small particles was responsible for the observed red shift.

Applications of magnetic nanoparticles, including hyperthermia for cancer treatments, require knowledge of how the colloidal enviromnent affects the magnetic properties of the nanoparticles. Here, 10 nm diameter cobalt nanoparticles synthesized by thermodecomposition in 1,2-diehlorobenzene (DCB) are used to study the effect of the colloidal environment on the magnetic behavior of such materials. The magnetic properties are investigated by magnetization (M) versus temperature (T) measurements and vector magnetometry performed on the samples under zero-field-cooled conditions. Of particular interest in the M versus T data is a continuous rise in the magnetization observed around the DCB melting point during sample heating and a discontinuous drop around the DCB supercooling point during sample cooling. Vector magnetometer measurements quantify the portion of the sample that does not respond to the applied field. The magnitude of this unreversed component doubles with decreasing temperature as the temperature cools through the supercooling point in DCB. There is also an increase in the uniaxiai anisotropy of the sample from 61.1(7) x [10.sup.-7] J to 104.2(9) x [10.sup.-7] J as the liquid-to-solid transition is traversed. Index Terms--Cobalt, magnetic anisotropy, magnetic nanoparticles, spin rotation.

The magneto-optical indicator film technique was used to investigate the hybrid exchange spring behavior in a bilayer consisting of an epitaxial film of Fe/Sm2Co7 deposited onto a Cr buffered MgO substrate. The results revealed unexpected dependence of the direction of average remanent magnetization on the external magnetic field direction and value.

The domain processes were seen at 300 K using the magneto-optic indicator film technique (MOIF) in an exchange-coupled ferromagnet (FM)/antiferromagnet (AF) bilayer Fe(sub 76)Mn(sub 6)C(sub 18)/FeMn deposited under the presence of a 0.4 mT magnetic field (H) applied in the plane of the sample. The results prove that the AF domain walls do not move during the motion of FM domain walls and that an exchange spring is created parallel to the AF/FM interface as the ferromagnetic layer reverses.

Magneto-optical indicator film technique was used for examining the magnetization reversal in coupled ferromagnetic Co/Ru/Co trilayers deposited on obliquely sputtered Ta underlayers. An anomalous magnetization reversal was observed and the angle between the magnetization vectors in the adjacent domains was revealed to be plusmn 100 degree.

Macroscopic domain structures have been realized in wedged-permalloy (Py)/uniform-FeMn bilayers during magnetization reversal. While the exchange field remains practically the same in both geometries, the coercivity and squareness of the loop are much less in the parallel geometry.

The magnetization reversal of epitaxial NiO/NiFe bilayers grown on single crystal (001) MgO and polycrystalline Si substrates have been studied, using the magneto-optical indicator film (MOIF) method. The unidirectional-axis magnetization reversal was found to proceed by domain nucleation and growth. An asymmetry in the activity of the domain nucleation was revealed, and bilayer remagnetization was found to be ruled by defect structures in the antiferromagnetic layer.

A study of the magnetic moments of colloidal silica and potassium silicate gel/iron nanocomposites revealed that Fe and gel/Fe nanocomposites exhibit different magnetic moments. The pore structures of the potassium silica gel used to prepare these materials were responsible for the difference. The materials were obtained when ferric nitrate solution was infiltrated into a colloidal silica.

The enhanced magnetocaloric characteristics of the iron-substituted gadolinium garnet series Gd3Ga5-xFexO12 (GGIG) were studied theoretically. It was shown that the entropy change of GGIG at applied fields of 0.9 and 5.0 T was much greater than that observed in Gd3Ga5O12. At low Fe concentrations, the magnetic chracteristics and thermodynamic properties of GGIG were consistent with those of magnetically ordered clusters.

The influence of uniaxial magnetic anisotropy on the magnetocaloric effect was investigated using Monte Carlo simulations. The results showed that for operation of a magnetic refrigeration cycle near the magnet's Curie temperature, the applied field should be normal to the easy plane of magnetization.

Magnetometry and neutron scattering are used for analyzing the magnetic properties of pressure-graded Co/Pd multilayers. Complementary magnetometry results have shown that the graded magnetic profiles are because of a decrease in saturation magnetization for regions deposited at higher pressure and the increased deposition pressure has shown increased coercivity.

The structure and magnetocaoloric properties of the Fe-doped HoTiGe compound were investigated in order to determine whether the field-induced magnetic transition in the compound involves a crystallographic phase change and whether Fe doping would eliminate the hysteresis losses. This is done by using scanning electron, microscopy (SEM), energy dispersive spectroscopy, X-ray diffraction, magnetometry, and calorimetry.

The magnetocaloric effects of five FeCiCrZrB amorphous alloys [{[Fe.sub.x][Co.sub.y][Cr.sub.z]}.sub91][Zr.sub.7][B.sub.2] with Fe:CO:Cr ratios of 100:0:0, 90:15:5, 85:5:10 and 75:15:10] chosen for efficiently surveying the high [T.sub.c] metallic glass composition surface are reported. The refrigeration constant (RC) values computed by Wood-Potter method are seen to favorably compare with values reported for other refrigerant materials.

Powder X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and magnetometry were used to investigate the structural and magnetic properties of arc-melted and homogenized alloys of [Gd.sub.5][Ge.sub.2][Si.sub.2].[X.sub.0.1] (X=Co, Cu, Ga, Mn, Al, Bi, Sn). It is observed that the addition of the small metals completely eliminated the large hysteresis losses present in the undoped [Gd.sub.5][Ge.sub.2][Si.sub.2] between 270 and 330 Kelvin.

The properties of incommensurate spin density waves (SDWs) in iron aluminides are examined by neutron diffraction in Fe(Al). Forty-eight wave vectors of magnitude almost equal to the {110} wave vectors of the bcc lattice are existing for stabilization of the SDWs by spanning the Fermi surface.

The imaging of the magnetic domain structure in a Tb40Fe60/Fe50Co50 multilayer with the help of a magneto-optic indicator film technique is discussed. Magnetization vectors rotated under application of stress and recovered upon removal of stress without domain wall motion.

The magentocaloric characteristics of several AlxGdyFez (with x+y+z=100) ternary alloys between 2 and 300 K are examined. Alloys above 60 K display Superparamagentic behavior and the alloys possess enhanced deltaSm values.