The influence of growth temperature Ts (300–773 K) on the structural phase ordering, static and dynamic magnetization behaviour has been investigated in ion beam sputtered full Heusler alloy Co2FeAl (CFA) thin films on industrially important Si(100) substrate. The B2 type magnetic ordering is established in these films based on the clear observation of the (200) diffraction peak. These ion beam sputtered CFA films possess very small surface roughness of the order of subatomic dimensions (<3 Å) as determined from the fitting of XRR spectra and also by AFM imaging. This is supported by the occurrence of distinct Kiessig fringes spanning over the whole scanning range (~4°) in the x-ray reflectivity (XRR) spectra. The Gilbert damping constant α and effective magnetization 4πMeff are found to vary from 0.0053 ± 0.0002 to 0.0015 ± 0.0001 and 13.45 ± 00.03 kG to 14.03 ± 0.04 kG, respectively. These Co2FeAl films possess saturation magnetization ranging from 4.82 ± 0.09 to 5.22 ± 0.10 μB/f.u. consistent with the bulk L21-type ordering. A record low α-value of 0.0015 is obtained for Co2FeAl films deposited on Si substrate at Ts ~ 573 K.

We present experimental results on single crystal CeRu 2 showing that the extent of history dependence of peak-effect depends on the path followed in the space of field (H) and temperature ( T ). The (H,T) regime over which history effect is observed is larger if the vortex lattice is prepared by lowering T from above T C in constant H i.e. by field cooling. We compare this history effect with the very recently reported history dependence of peak-effect in detwinned single crystals of YBaCuO, highlighting the similarities and differences. We discuss the possibility of a first order vortex solid-solid transition in CeRu 2 within the realm of recent theoretical developments in the field of vortex matter.Typeset using REVT E X 1 Recent theoretical 1-4 and experimental 5-7 studies based on high T C superconductors (HTSC) suggest the existence of at least two distinctly resolved solid phases of vortex matter which are distinguished from the high-temperature high-field vortex liquid. These two vortex solid phases are referred to as low-field quasi-ordered solid or Bragg-glass and highfield disordered solid or vortex-glass (see Ref.8). The important question now is, what is the the order of the thermodynamic phase transitions (if any) between the various vortex phases?The Bragg-glass has long range order and it is expected to melt to vortex liquid at high temperature through a first order transition. Experimentally, the indication of a first order transition usually comes via a hysteretic behaviour of various properties, not necessarily thermodynamic ones. In HTSC samples also initial suggestions of a first order melting transition came via distinct hysteresis observed in transport property measurements 9-11 . The confirmatory tests of first order transition ofcourse involve the detection of discontinuous change in thermodynamic observables and the estimation of latent heat, and this has subsequently been achieved for vortex melting in HTSC materials through magnetization 12,13 and calorimetric measurements 14 . There also exists a less rigorous class of experimental tests which involves the study of phase co-existence and supercooling across a first order transtion. This kind of experiment has also come out to be pretty informative for the first order melting transition of the Bragg-glass in Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO) (Ref.15).With the establishment of the first order nature of the Bragg-glass to vortex liquid transition line, the focus in the recent years has shifted to the Bragg-glass to vortex-glass transition. In various HTSC materials peak-effect(PE) or fish-tail is used to track this field induced transition from Bragg-glass to vortex-glass, and this transition is obsereved to be a sharp transtion 5-7 . However, the exact nature of this transition -whether it is a continuous or a first order transition-is not established yet. Very recent magneto-optics studies on single crystal samples of BSCCO claim the presence of phase-coexistence 16,17 and supercooling 17 across the Bragg-glass-vortex-glass phase transiti...