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Magnetic phases in evaporated thin films of Ge100−xFex (x in at.%) alloys with x = 36.6 and 51.8 are examined. At x = 36.6, a single amorphous phase is formed. The magnetic phase at room temperature appears to be ferromagnetic, and it transforms into a spin-glass phase at 20 K. The magnetic phases are more complicated at the higher Fe composition of x = 51.8, which is mainly due to the presence of Fe precipitates in the amorphous matrix. An analysis based on the superparamagnetism indicates that the effective composition of the amorphous phase is estimated to be x = 39.4, and this amorphous phase shows a similar magnetic behaviour to that observed in the x = 36.6 sample with the exception of a slightly higher spin freezing temperature of 30 K. Due to the Fe precipitates, an additional superparamagnetic behaviour is observed with a blocking temperature of 160 K. Magnetization saturation in the spin-glass state occurs at a relatively small applied field, which indicates that the direct antiferromagnetic exchange coupling between Fe ions is weak.

The effects of inserting an amorphous FeZr layer between the [Pt/Co] multilayer and the CoFeB/MgO layer in stacks possessing perpendicular magnetic anisotropy are examined. A 1-nm-thick FeZr layer is effective in forming a bcc (001)-textured CoFe layer during annealing by suppression of crystallization at the interface with the multilayer, which is terminated in a close-packed plane. Because FeZr is magnetic, it has an advantage over Ta, an alternative material used for the same purpose. Efficient magnetic coupling between the multilayer and CoFeB/MgO occurs even for large FeZr layer thicknesses, so the magnetic properties of the stack are only weakly affected.

Unusual negative remanent magnetization (NRM) behavior is examined in a single-domain particle with two uniaxial anisotropies. NRM occurs in a narrow window of the parameters, which include the direction of the applied magnetic field and the angle and relative strengths of the two uniaxial anisotropies. However, these parameters are not independent of each other because changes occur in the angle between the two uniaxial anisotropies through their interactions. It is found that the anisotropy interactions are stronger at smaller crossing angles and at greater relative strengths of the two anisotropies, resulting in subsequent changes in NRM behavior.

A new plasma process, i.e. a combination of plasma immersion ion implantation and deposition (PIIID) and high power impulse magnetron sputtering (HiPIMS), was developed to implant non-gaseous ions into material surfaces. The new process has the great advantage that thin film deposition and non-gaseous ion implantation can be achieved in a single plasma chamber. In this study, Ge ions were successfully implanted into SiO(2) thin film, which resulted in uniformly and homogeneously distributed crystalline Ge quantum dots (Ge-QDs) embedded in a SiO(2) matrix even without a further annealing process. Broader areas of application of PIIID technology are envisaged with this newly developed process.

The strong perpendicular magnetic anisotropy (PMA), indicated by a large coercivity of 590 Oe, is obtained in CoFeB/Pd multilayers through a systematic study that involves using various substrates (Si, glass, sapphire, and MgO) and seed layers (Al and Ta) and also varying the thickness of the seed layer. The PMA is nearly independent of the substrate when Al is used as a seed layer, but the dependence increases significantly with increasing seed layer thickness. The behavior becomes rather complicated for the multilayers with a Ta seed layer, showing a large substrate dependence and a large seed layer thickness dependence.

In this paper we report the study of boron substituted SmFe2 compounds belonging to the family of giant magnetostrictive materials RFe2(R=Tb, Dy, Sm). The dc magnetization up to fields of 60 kOe and low field ac sucsceptibility has been measured in the temperature range 5-300 K. In SmFe2, the temperature dependence of magnetization shows two magnetic transitions at 190 K and 80K in the zero field cooled state. The lower temperature transition is suppressed by the addition of even 1at%B as observed from the dc magnetization. The ac susceptibility shows a pronounced maximum close to 80 K in both the parent compound and in 1 at% B substituted one. This transition presumably occurs due to freezing of domain wall motion.

Methods are described in this study to predict the magnetic configuration at the saddle point in nanostructured cells of single magnetic thin films and synthetic antiferromagnets. The prediction is done indirectly by calculating the self-demagnetizing field at the saddle point, which is then compared with the value calculated under the ideal single domain state. The saddle point magnetic configuration in the single magnetic thin films deviates more from the ideal single domain state than in the synthetic antiferromagnets. As the cell geometry varies from rectangle to ellipse, the deviation decreases monotonically in the single magnetic thin films, while it remains nearly constant in the synthetic antiferromagnets.

Three-dimensional numerical calculations based on the finite element method are performed to calculate the increase in the temperature in nanostructured cells of a magnetic tunnel junction under conditions that are relevant to current-induced magnetization switching for a high-density magnetic random access memory. Three key parameters, the lateral size, the resistance-area product and the applied current density, were varied widely so that their effects on the temperature increase could be examined. The computed results for the temperature increase, as a function of the resistance-area product and the current density, show the same trends that are expected from an equation for the dissipated heat. While the increase in the temperature is expected to be independent of the lateral size, the computations reveal a rather complicated relationship between the two variables, which is contingent on the various conditions that are considered. In a cell array that is relevant to high-density contexts, the temperature increase in the nearest cells is as high as 50% of the cell at which the current is directly applied; this could cause a thermal-stability problem in high-density magnetic random access memories. The temperature increase was also calculated under a more realistic physical picture of the relaxation of tunnelled electrons. These results are in agreement with those that are computed from Joule heating.

The variation of the magnetic energy barrier of nanostructured single-layered thin films according to the cell shape is calculated by a micromagnetic simulation. The magnetic energy barrier increases significantly as the cell shape varies from a rectangle to an ellipse. This behaviour, which can raise a serious reliability issue considering the difficulty in the precise shape control of the nanostructured cells, is due to the fact that the magnetization process occurs in a more coherent way as the cell shape more closely resembles an ellipse. The simple assumption of the single domain state significantly overestimates the magnetic energy barrier, in particular, near the rectangular geometry.

An analytical/numerical combined method is used in this study to calculate the magnetic energy barrier of a nanostructured synthetic antiferromagnet, Co?Fe?B (2?nm)/Ru (0.6?nm)/Co?Fe?B (2?nm), with lateral dimensions of 160?nm ? 80?nm. A key to the method is the use of the effective magnetostatic fields which are acquired by averaging over the entire magnetic layers. These effective fields are then used as inputs in an analytical equation for the total energy. Systematic calculations are performed, even considering the effects of edge rounding during nanofabrication, and the calculated magnetic energy barriers agree with the experimental value reported in the literature from the current induced magnetization switching experiments obtained by using the Slonczewski equation.

Magnetic measurements are performed under ac and dc conditions on well characterized Ge100−xMnx (x in at.%) amorphous thin films prepared by thermal co-evaporation onto oxidized Si or glass substrates at room temperature. M–H hysteresis loops at 5 K show that saturation does not occur even at a high applied field of 30 or 50 kOe. The temperature dependence of the dc and ac susceptibility shows a cusp with a position and magnitude that vary with the frequency during the ac susceptibility measurements. These results suggest a spin glass behaviour at low temperatures. Two competing magnetic interactions between Mn ions, which are responsible for the spin glass behaviour, are considered to be the direct antiferromagnetic coupling and the indirect ferromagnetic coupling through conduction electrons or holes. Scaling analysis indicates that the indirect ferromagnetic interactions are long range.