A. K. Grover

The Y-Co system: a partial phase diagram study

Abstract In conjunction with magnetic and superconductive studies the phase diagram in the region 25%–50% Co was clarified. While Y 3 Co, Y 8 Co 5 and YCo form by peritectic reactions, the other phase in this range, formerly thought to be Y 4 Co 3 and now shown to be Y 9 Co 7 , forms by a peritectoid reaction at 725 °C. A complication in as-cast alloys of 38%–40% Co is the appearance of a metastable Y 3 Co 2 phase.

A.C. susceptibility measurements in the presence of D.C. magnetic fields in CoGa alloys — A cluster spin glass system

Abstract Low field a.c. susceptibility measurements in the presence of large d.c. magnetic fields are reported on CoxGa1−x alloys (x = 0.585, 0.60 and 0.63), a cluster spin glass system, in the temperature range of 77 to 500 K. A peak in the a.c. susceptibility is observed in each case. The peak position shifts towards lower temperatures with increasing d.c. magnetic fields. In conjunction with the zero field NMR measurements reported earlier, these results may be taken to imply the existence of a continuous spectrum of freezing temperatures — cluster with highest anisotropy field having the lowest freezing temperature.

The hybrid state of the magnetic superconductor Y9Co7

The new results of resistance, low-field magnetoresistance and AC susceptibility measurements in Y9Co7 show that the superconducting interactions coexist with strong magnetic correlations up to about 5.5K. This hybrid state has some very interesting magnetic properties.

Host and impurity NMR studies in CoGa alloys - a cluster spin glass system

Abstract The Co x Ga 1-x alloys having CsCl structure contain nonmagnetic Co and Ga atoms (host) and magnetic Co atoms (impurities) for x ≳ 0.50. We report here the simultaneous observation of the applied field NMR of host nuclei and the zero field resonance (ZFR) of impurity nuclei. From the ac susceptibility measurements and the field dependence of ZFR signals we conclude that for 0.50 ≲ × ≲ 0.64, this system is a “cluster spin glass”.

Do ruthenium atoms possess local moment in the magnetically ordered system Fe3−xRuxSi (?)

Abstract Magnetization and the 57 Fe hyperfine field values show a very small variation on substitution of Fe with Ru atoms in the ferromagnetic alloys Fe 3−x Ru x Si for x values as large as 1.35. The data are strongly suggestive of the presence of moment of ∼ 1 μ B at Ru atoms.

RuFeSi — A new magnetic system

Abstract A ternary system consisting of Ru, Fe and Si is identified in which the hyperfine field at Fe is seen to evolve at a characteristic temperature, T ∗ , far below the magnetic ordering temperature, T m . It is speculated that the magnetic ordering at T m is itinerant and T ∗ corresponds to the localization of the majority spin electrons at the Fe atoms.

Hyperfine Fields in Cobalt-Based Heusler Alloys

Hyperfine fields measured by NMR at various nuclear sites in ferromagnetic cobalt-based Heusler alloys Co 2 TSn (T=Ti, Zr, Hf, Nb), Co 2 TAl (T=Ti, Zr, Hf, V) and Co 2 VGa are reported.

Peaks in low field a.c. susceptibility of ferromagnetic Heusler alloys

Abstract The observation of a peak in the low field susceptibility need not always be taken to imply spin glass type of freezing. It may also be the consequence of a rapid build up of anisotropy field below the ordering temperature. The results of low field a.c. susceptibility measurements on Ru and Rh based ferromagnetic Heusler alloys presented here substantiate the above statement.

Hyperfine fields in Sm1−xGdxAl2 alloys—Microscopic evidence for ferromagnetic coupling between rare earth spins

The results of hyperfine field studies on Sm1−xGdxAl2 alloys for 0?x?0.5 are reported. The hyperfine field at Al, H(Al), has been measured to be +32.5 kOe in SmAl2 and −47 kOe in GdAl2. In Sm1−xGdxAl2 alloys, we find that the magnitude of H(Al) increases with increasing x and further H(Al) becomes negative even with small replacement of Sm by Gd. H(Al) in these compounds is proportional to the average value of spin per rare earth ion. The observed behaviour can be understood in terms of a ferromagnetic coupling between the spins of Sm and Gd.

Evidence against the existence of unstable magnetic moments in the system Ce(Fe1-xCox)2

57Fe Mossbauer studies in the system Ce(Fe1-xCox)2 for x=0.15 and 0.25 have shown the sudden loss in magnetisation in this system, well bellow the onset of long-range ferromagnetic order, arises due to the reorientation and locking of Fe moments in such a way as to produce almost zero net magnetisation. The thermal variation of the average hyperfine field, however, does not have any signature of the reorientation transition temperature.