Localization and magnetism of Fe replacing either Mn or Ni in the Ni2Mn1.44Sn0.56-type Heusler alloy have been systematically investigated using magnetization, scanning electron microscopy and Mössbauer spectroscopy. It has been shown that the addition of Fe either in Mn or in Ni sites reduces the fraction of the Mn-rich NiMnSn-type Heusler alloys that has short-range antiferromagnetic interactions; consequently it reduces the martensitic–austenitic transition temperature and increases the thermal hysteresis width due to an increase in atomic disorder caused by Fe replacements. The Fe atoms in Mn sites have two magnetic configurations with magnetic moments of 0.8μB/Fe and 1.4μB/Fe in the martensitic orthorhombic structure, while Fe in Ni sites have magnetic moments smaller than 0.1μB/Fe. These results indicate that the Fe atoms are distinctly substituting either Mn or Ni and the decrease in the martensitic phase transition temperature for increasing Fe content can be mainly attributed to the Fe atoms in the Mn sites in both cases.

We study the transport properties of C 1Àx Co x thin films (with x ¼ 0.1, 0.15 and 0.2) grown on Si substrate by pulsed laser deposition technique. The results demonstrate some anomalous effects in the behavior of the measured resistance R(T,x). More specifically, for 0 < T < T * range (with T * x 220 K), the resistance is shown to be well fitted by a small polaron hopping scenario with R h ðT; xÞfexp n T0ðxÞ T 0:5o and a characteristic temperature T 0 ðxÞxT 0 ð0Þð1 À xÞ (with T 0 (0) ¼ 120 K). While for higher temperatures T * < T < T C (x), the resistance is found to be linearly dependent on spontaneous magnetization M(T,x), viz. R M (T,x)fM(T,x), following the pattern dictated by electron scattering on cobalt atoms formed robust ferromagnetic structure with the Curie temperature T C (x) obeying a percolation like law T C ðxÞxT C ðx m Þðx=x m Þ 0:15 with T C (x m) ¼ 295 K and the maximum zero-temperature magnetization reaching Mð0; x m Þx0:5m B per Co atom for x m ¼ 0.2.

We present a comparative study on the influence of applied magnetic field on the resistance of C 1−x Co x thin films (with x = 0.1, 0.15 and 0.2) grown on Si substrate by pulsed laser deposition technique. It is found that the behavior of magnetoresistance (MR) drastically depends on the temperature. Namely, at low temperatures MR is positive and its behavior is governed by the field mediated weak localization scenario. While at high temperatures MR turns negative and its behavior is dominated by electron scattering on ferromagnetic cobalt atoms.

We present our recent results on temperature behavior of magnetization observed in N i47M n39In14 Heusler alloys. Three regions can be distinguished in the M −T diagram: (I) low temperature martensitic phase (with the Curie temperature TCM = 140K), (II) intermediate mixed phase (with the critical temperature TMS = 230K) exhibiting a reentrant like behavior (between TCM and TMS), and (III) high temperature austenitic phase (with the Curie temperature TCA = 320K) exhibiting a rather wide plateau region (between TMS and TCA). By arguing that powerful structural transformations, causing drastic modifications of the domain structure in alloys, would also trigger strong fluctuations of the order parameters throughout the entire M − T diagram, we were able to successfully fit all the data by incorporating Gaussian fluctuations (both above and below the above three critical temperatures) into the Ginzburg-Landau scenario.