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Hydrides of LaFe11.57Si1.43 intermetallic compound have been prepared by high-energy ball milling in the presence of hydrogen gas, a process known as reactive milling. The Curie temperature of the samples was tuned within the temperature range of 199 K to 346 K by changing the hydrogen content from 0 to 2.3 at. % without compromising much of the magnitude of the magnetocaloric effect. Arrott plots and large hysteresis in the magnetization vs magnetic field curves confirm that the first-order itinerant-electron metamagnetic transition is the reason for large entropy change in the parent as well as in the hydride samples. The present study indicates that reactive milling can be an effective method for incorporating interstitial hydrogen within these compounds in order to raise their TC to room temperature. [ABSTRACT FROM AUTHOR]

Nd80Fe20 bulk specimens were prepared by copper mold casting and their structure and magnetic properties were studied. The specimens contain 73 wt % elemental Nd and 27 wt % hard magnetic Fe–Nd regions, which are a mixture of amorphous and nanocrystalline phases. The average composition of the Fe–Nd regions is Nd45Fe55. The presence of elemental Nd leads to multiple magnetic transitions below 30 K whereas the Fe–Nd regions have a Curie temperature of 529 K. Above 30 K, the specimens show a single-phase hard magnetic behavior superimposed on the large susceptibility due to paramagnetic Nd and a noncollinear magnetic structure of Fe moments. At T<=30 K, two-phase demagnetization curves were observed due to the additional ferromagnetic contribution of metastable fcc Nd. The coercivity of the hard magnetic Fe–Nd regions is strongly temperature dependent, decreasing from 6.4 T at 4.2 K to almost zero at temperatures close to the Curie temperature. The shape of the initial magnetization curve and the remanence values of about half of the maximum magnetization (at 40 T) suggest coherent rotation as the magnetization reversal mechanism for the Fe–Nd regions. The demagnetization curves can be fitted by a modified Stoner-Wohlfarth model of weakly coupled single-domain particles with sizable high-field susceptibility to account for the noncollinear magnetic order. The saturation magnetization, the anisotropy fields, and the high-field susceptibility values of the hard magnetic Fe–Nd regions are deduced from the fits in the temperature range of 75–290 K. [ABSTRACT FROM AUTHOR]

Nd80Fe20 bulk specimens were prepared by copper mold casting and their structure and magnetic properties were studied. The specimens contain 73 wt % elemental Nd and 27 wt % hard magnetic Fe–Nd regions, which are a mixture of amorphous and nanocrystalline phases. The average composition of the Fe–Nd regions is Nd45Fe55. The presence of elemental Nd leads to multiple magnetic transitions below 30 K whereas the Fe–Nd regions have a Curie temperature of 529 K. Above 30 K, the specimens show a single-phase hard magnetic behavior superimposed on the large susceptibility due to paramagnetic Nd and a noncollinear magnetic structure of Fe moments. At T<=30 K, two-phase demagnetization curves were observed due to the additional ferromagnetic contribution of metastable fcc Nd. The coercivity of the hard magnetic Fe–Nd regions is strongly temperature dependent, decreasing from 6.4 T at 4.2 K to almost zero at temperatures close to the Curie temperature. The shape of the initial magnetization curve and the remanence values of about half of the maximum magnetization (at 40 T) suggest coherent rotation as the magnetization reversal mechanism for the Fe–Nd regions. The demagnetization curves can be fitted by a modified Stoner-Wohlfarth model of weakly coupled single-domain particles with sizable high-field susceptibility to account for the noncollinear magnetic order. The saturation magnetization, the anisotropy fields, and the high-field susceptibility values of the hard magnetic Fe–Nd regions are deduced from the fits in the temperature range of 75–290 K. [ABSTRACT FROM AUTHOR]

Hydrides of La[Fe.sub.11.57][Si.sub.1.43] intermetallic compound are prepared by high-energy ball milling in the presence of hydrogen gas, which is also called as reactive milling. The results have shown that reactive milling can be used for incorporating interstitial hydrogen within these compounds in order to raise their Curie temperature to room temperature.

The study of the effects of composition and cooling rate on the structure and the magnetic entropy change in Gd5Si(sub x)Ge(sub 4-x) (x=1.7,2) is discussed. The Gd5Si2Ge2-type phase in the Gd5Si2Ge2 alloy is found to be metastable at room temperature and stable in the Gd5Si1.7Ge2.3 alloy.

The ferrimagnetic compounds Ca(CuxMn3 – x)Mn4O12 of the double distorted perovskites AC3B4O12 family exhibit a rapid increase of the ferromagnetic component in magnetization at partial substitution of square coordinated (Mn3+)C for (Cu2+)C. In the transport properties, this is seen as a change of the semiconducting type of resistivity for the metallic one. The evolution of magnetic properties of Ca(CuxMn3 – x)Mn4O12 is driven by strong antiferromagnetic exchange interaction of (Cu2+)C with (Mn3+/Mn 4+)B coordinated octahedra. The competing interactions of (Mn3+)C with (Mn3+/ Mn4+)B lead to the formation of noncollinear magnetic structures that can be aligned by magnetic fields. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

Abstract: The strong influence of Cu substitution on the magnetic properties of SmCo5, especially on the coercive field, is well known. Induction-melted samples () show a phase separation within the 1:5 structure. An unusual jump from a low to a high magnetisation state in an increasing external field is observed. Using pulse field, high coercive forces up to about μ 0 J H c≈30T and a high critical field μ 0 H U for the unusual jump reaching 45T at 4.2K for are observed for the first time. H c and H U increase with decreasing temperature. An influence of the field changing rate on the measured H U is found. [Copyright &y& Elsevier]

The formation of phases has been studied for the structural transition between two types of 1–6–6 rare earth–transition metal–metal crystalline phases in the pseudo-binary alloy series Dy(Mn6Ge6)1-x(Fe6Al6)x. In equilibrium, the limiting composition DyMn6Ge6 (x=0) is known as a helimagnet with hexagonal HfFe6Ge6-type structure (P6/mmm). DyFe6Al6 is a ferrimagnetic compound with partially disordered CeMn4Al8-type structure (I4/mmm). Both compounds show high magnetic transition temperatures of 423 and 340 K, respectively. Samples with compositions x=0–1 were prepared by arc melting, subsequent melt spinning, and annealing in Ar. The structure of the samples was checked by X-ray diffraction (XRD) both in as-spun and annealed state. After quenching, the composition DyMn6Ge6 (x=0) yields a distorted crystalline structure derived from the hexagonal TbCu7-type. For x≥1/2, annealing has little effect on the crystal structure determined by XRD. Here as-spun samples are crystalline with a structure derived from the equilibrium tetragonal CeMn4Al8-type and may contain an additional crystalline constituent. Magnetoresistive and magnetic properties of these systems are used to characterise the different structures. In particular, annealing modifies the magnetism in DyFe6Al6 (x=1) samples, and (FeAl)-substitution deteriorates the remarkable room temperature magnetoresistance properties of DyMn6Ge6. [Copyright &y& Elsevier]

Amorphous states have been found in rapidly quenched alloys in the pseudoternary system DyMn6-x-yFex+yGe6-xAlx (x,y=0 to 6). The amorphous state is formed in competition to the crystallization of ternary (1-6-6 rare earth-transition metal-metal) compounds. The melt-spun ribbons were investigated by x-ray diffraction, high resolution transmission electron microscopy, differential scanning calorimetry, and magnetization measurements. All amorphous samples exhibit multistep crystallization behavior without a clear indication for a glass transition below the first exothermic effect. Some of the amorphous alloys exhibit a magnetic ordering above room temperature and complex magnetic transitions similar to the properties of crystalline 1-6-6 compounds. [ABSTRACT FROM AUTHOR]

Magnetocaloric effect (MCE) in low-cost iron-based binary alloys R2Fe17 (R = Y, Pr) has been investigated by measuring their magnetic properties. The Curie temperature of these alloys is found to be close to room temperature. The specific heat measurement of these materials indicates a second order ferromagnetic/paramagnetic phase transition. The MCE properties in these alloys are comparable to that of gadolinium, which is very expensive for domestic use. Therefore these binary alloys are suitable as room temperature MCE materials. The effect of pulsed magnetic field on the MCE properties has also been studied up to 25 T. [ABSTRACT FROM AUTHOR]