S.N. Shringi

SPUTTER DEPOSITED STRONTIUM FERRITE FILMS WITH C-AXIS ORIENTED NORMAL TO THE FILM PLANE

M‐type strontium ferrite films were deposited by radio‐frequency (rf) sputtering on fused quartz substrates kept at ambient temperatures. The as‐deposited films were amorphous. They crystallized on annealing at a temperature of 800 °C or higher. The films deposited at low rf power and low oxygen to argon ratio showed c‐axis orientation normal to the film plane. The magnetic properties of these films were studied using vibrating sample magnetometer, polar Kerr rotation, and torque magnetometer. The perpendicular M‐H loops for c‐axis oriented films were nearly rectangular with coercivity of the order of 3 kOe.

Preparation and magnetic properties of strontium ferrite thin films

Strontium ferrite films were deposited by RF sputtering of a commercial strontium ferrite target onto fused quartz substrates maintained at temperatures up to 900 degrees C. Films deposited at T 800 degrees C had crystalline M-type strontium ferrite structures. The thin composition corresponded to that of the target. Films deposited at 800 degrees C were partially oriented in the [110] direction with the c-axis in the plane. Postannealing led to an increase in the magnetization, indicating incomplete formation of ferrite in the as-deposited state. Both in-plane and perpendicular hysteresis loops are rectangular with remanence ratios of 0.8 and 0.6, respectively, showing partial orientation with the c-axis. The torque curve is consistent with the above, although there are some additional anomalous peaks. >

Selective synthesis of light alkenes from carbon monoxide and hydrogen on silicalite supported iron-manganese catalysts

Abstract Iron-manganese catalyst supported on silicalite 1 was prepared by impregnation. The catalyst preparation was followed by X-ray diffraction, temperature-programmed reduction and Mossbauer spectroscopy. Hydrogenation of CO was studied in a high pressure reactor by varying CO:H2 ratio, temperature, and pressure. The silicalite supported catalyst shows very high selectivity for C2-C4 alkenes. When acidic ZSM-5 having the same structure as silicalite 1 was used as the support, the product had very little alkenes. Addition of 0.2% potassium improves the alkene selectivity of the Fe-Mn on the silicalite catalyst.

Low temperature resistivity studies in Cr containing amorphous alloys Fe-Ni-Cr-Mo-Si-B

Resistivity data on Fe 40-x/2 Ni 40-x/2 Cr x Mo 2 Si 10 B 8 samples with x = 0,1,3,4,5 in the temperature region 7 K - 300 K have been reported. A minimum is observed in the resistivity as a function of temperature at a temperature T min varying between 20 K to 80 K for the five samples. Attempts are made to fit the data with a sum of a T2term and various functional forms predicted for the negative temperature coefficient region.

Sputter deposited LiZn ferrite films on fused quartz substrates

Abstract Lithium-zinc ferrite thin films have been deposited by rf sputtering technique on amorphous fused quartz substrates. The as-deposited films were amorphous and crystallization took place when the films were annealed at 800°C. The observed magnetization values varied from 34 to 60% of that of the bulk. The coercivity was found to be in the range 35–42 Oe.

Mossbauer study of interface mixing in FE/NI multilayers

Abstract Conversion Electron Mossbauer Spectroscopy (CEMS) studies were carried out on as deposited and annealed Fe Ni multilayers prepared by rf sputtering, in order to probe the interface. A series of multilayers in which Ni layer thickness was fixed at 25 A and the Fe layer thickness was varied from 18 to 120 A, were studied. The width of the Mossbauer lines increases with decreasing Fe layer thickness indicating a mixing at the interface, which was analyzed using specific models.

Magnetic and conversion electron Mössbauer spectroscopy studies in Fe/Ta multilayers

We have prepared Fe/Ta multilayers by rf sputtering. A small 1‐cm2 chip of 57Fe was placed on the Fe target. We studied the magnetization (M) and M‐H loops and also carried out conversion electron Mossbauer spectroscopy (CEMS). The in‐plane loops are rectangular with a lowest coercivity of 2.6 Oe. Magnetization studies indicate a dead Fe layer about 5 A thick at each interface. CEMS spectra for samples with t(Fe)≥54 A showed a typical six‐line pattern, indicating the presence of bulk Fe. No other Fe sites could be detected. However, for t(Fe)=24 A, where almost 50% of Fe is nonmagnetic, CEMS spectra showed the presence of a strong paramagnetic doublet.

The change in the temperature coefficient of resistivity with Mn addition in Fe‐ and Co‐rich amorphous alloys

Electrical resistivity studies have been carried out on a‐Co80−x−yFexMnyB12Si8 alloys for 10≤x≤70 and y=0,4,8. It has been found that the decrease of temperature coefficients of resistivity (TCR) with Mn substitution is significantly more in Fe‐rich alloys than in Co‐rich alloys. A T2 term is not found in Co‐rich alloys even up to the addition of 8 at. % of Mn. Although Fe‐rich alloys show a T2 dependence for 8 at. % of Mn, a second minimum is not observed. In the absence of Mn, the substitution of Fe for Co does not decrease the TCR while in the presence of Mn, the substitution of Fe does decrease the TCR.

Oriented strontium ferrite films sputtered onto Si(111)

Abstract Recently we have shown that M-type Sr ferrite films (SrM) can be sputter deposited on fused amorphous quartz substrates with c -axis normal to the film plane [1]. In the present study we show that the c -axis orientation of SrM on Si(111) can be tailored to vary from in plane to normal to the film plane by changing the deposition parameters.

A study of anisotropic magnetoresistance in a-FeNiMnBSi alloys

Longitudinal and transverse magnetoresistivity measurements have been performed on a-Fe40-xNi40MnxB12Si8 alloys (0<or=x<or=5.5) in fields up to 40 kG, at 4.2 K, 100 K, 200 K, and 300 K. Above technical saturation, all the alloys exhibit a negative slope, i.e. the resistivity decreases as a function of the magnetic field. The high-field magnetoresistivity slope becomes more and more negative with increasing Mn concentration. Assuming that the negative slope of magnetoresistance is caused by the suppression of spin waves, the temperature and composition dependence of magnetoresistivity of the present series could be qualitatively understood. The spin-wave contribution to the zero-field resistivity has been estimated using a simplified approach. Furthermore, the ferromagnetic anisotropy of resistivity (FAR) has been calculated and the results are analysed in the light of a two-current conduction model generalized to weak ferromagnets and amorphous alloys.