Anti-site-induced diverse diluted magnetism in LiMgPdSb-type CoMnTiSi alloy

Exotic magnetic behaviour and evidence of cluster glass and Griffiths like phase in Heusler alloys Fe2-xMnxCrAl (0 ≤ x ≤ 1)

We present a detailed study of structural, magnetic and thermodynamic properties of a series of Heusler alloys Fe_2-xMn_xCrAl (x = 0, 0.25, 0.5, 0.75 and 1). Structural investigation of this series is carried out using high resolution synchrotron X-ray diffraction. Results suggest that with increasing Mn concentration, the L2₁ structure of Fe₂CrAl is destabilized. The DC magnetization results show a decrement in paramagnetic (PM) to ferromagnetic (FM) phase transition temperature (T_C) with increasing Mn concentration. From the systematic analysis of magnetic memory effect, heat capacity, time dependent magnetization, and DC field dependent AC susceptibility studies it is observed that, Fe₂CrAl exhibits cluster glass(CG)-like transition approximately at 3.9 K (T_f2). The alloys, Fe_1.75Mn_0.25CrAl and Fe_1.5Mn_0.5CrAl exhibit double CG-like transitions near T_f1 ~ 22 K, T_f2 ~ 4.2 K and T_f1 ~ 30.4 K, T_f2 ~ 9.5 K respectively, however, in Fe_1.25Mn_0.75CrAl, a single CG-like transition is noted at T_f2 ~ 11.5 K below T_C. Interestingly, FeMnCrAl shows the absence of long ranged magnetic ordering and this alloy undergoes three CG-like transitions at ~22 K (T_f^*), 16.6 K (T_f1) and 11 K (T_f2). At high temperatures, a detailed analysis of temperature response of inverse DC susceptibility clearly reveals the observation of Griffiths phase (GP) above 300 K (T*) in Fe₂CrAl and this phase persists with Mn concentration with a decrement in T*.

Lattice dynamics, mechanical stability and electronic structure of Fe-based Heusler semiconductors

The structural and mechanical stability of Fe₂TaAl and Fe₂TaGa alloys along with the electronic properties are explored with the help of density functional theory. On applying different approximations, the enhancement of semiconducting gap follows the trend as GGA < mBJ < GGA + U. The maximum forbidden gaps observed by GGA + U method are E_g = 1.80 eV for Fe₂TaAl and 1.30 eV for Fe₂TaGa. The elastic parameters are simulated to determine the strength and ductile nature of these materials. The phonon calculations determine the dynamical stability of all these materials because of the absence of any negative frequencies. Basic understandings of structural, elastic, mechanical and phonon properties of these alloys are studied first time in this report.

Unraveling the physical properties and superparamagnetism in anti-site disorder controlled Fe2TiSn

With an aim to control the anti-site disorder between Fe and Ti atoms in the full Heusler alloy, Fe[Formula: see text]TiSn, we substitute a small percentage of Ti at Fe site to form the Fe[Formula: see text]Ti[Formula: see text]Sn ([Formula: see text]) series. Using the incident x-rays tuned to the Fe K-edge absorption energy, we record the high resolution synchrotron x-ray diffraction profiles and unambiguously show the reduction in anti-site disorder. In particular, the Fe-Ti anti-site disorder decreases up to an excess Ti content of 0.07; further increase of Ti content leads to disorder between Ti-Sn sites. Detailed characterization vis-á-vis the excess Ti content has been carried out in terms of its thermal and electrical transport, and magnetic properties. Signatures of strong spin fluctuation are seen in all the physical properties reported here. The much disputed high value of the Sommerfeld constant has been shown to be a resultant of such strong spin fluctuations, thus ruling out the long standing controversy of heavy fermionic nature of Fe[Formula: see text]TiSn. Magnetization and the Seebeck coefficient show clear dependence on the disorder. Both dc and ac magnetic measurements reveal the low temperature superparamagnetic nature of this system, comprising of large magnetic clusters [Formula: see text]3 nm in size.