[en] In this study we have investigated the magnetic and electrical transport properties of Zr doped lanthanum manganite perovskite. The structural, magnetic, and transport properties of the Zr doped compounds were determined using x-ray diffraction, dc magnetic susceptibility, and a four probe method for electrical resistivity and magnetoresistance measurements in the temperature range of 5 - 400 K. The structure of the compounds was found to be rhombohedral. The magnetization versus temperature curves show ferromagnetic regions with the magnetic transition temperatures getting saturated for x≥0.07 compounds. The resistivity curves show decreasing resistivity with increasing Zr content in the compound. The resistivity of the compounds is very high and is explained as due to the localization tendency of the electrons. The metal - insulator transition temperature shows a compositional dependence and has additional contributions apart from magnetism. The results are explained by the double exchange interaction and Mn²⁺/Mn³⁺ ratio, and also by taking into account the competition between the core-spin interaction and double exchange interaction. [copyright] 2001 American Institute of Physics

[en] Magnetic susceptibility and magnetization of spin-density-wave (SDW) alloy systems (Cr+3.2%Co)_1-xMn_x and (Cr+6.5%Co)_1-xMn_x have been measured with a SQUID magnetometer. Magnetic properties of the studied alloys are compared with those exhibited by binary Cr_1-xMn_x and ternary (CrFe)_1-xMn_x and (CrSi)_1-xMn_x alloys. All these alloys show spin glass (SG)-like behavior; however, some of their magnetic properties are quite different from those exhibited by conventional metallic spin glasses. Though both Fe and Co produce a local moment in Cr and CrMn, addition of Co to CrMn does not result in suppression of SG-like phase like that in (CrFe)_1-xMn_x. This seems to be a result of essentially different strengths of Fe-Cr and Co-Cr couplings. All alloys studied show a low-temperature SG-like magnetic hysteresis. Such hysteresis is shifted to negative fields by cooling the alloys in a strong magnetic field through the Neel temperature. This effect is caused by unidirectional anisotropy of Co atoms frozen in the SDW matrix

[en] We have examined the magnetic phase diagram of single-crystal erbium in the temperature range between 60 K and 90 K and in applied magnetic fields along the c-axis up to 5.5 T using resistance versus temperature and magnetoresistance measurements. The H-T phase diagram for that region is presented. We have observed a splitting of the longitudinal Neel transition near 1.6 T. We have found a new phase with unknown structure in that portion of the phase diagram created by the splitting of the Neel transition. We have also found a multicritical point (P) at an applied field of 2.65 T and 71 K. A set of five magnetic phase lines appears to meet at this multicritical point. (author)

[en] We have studied polycrystalline La_0.83-xNd_xK_yMnO₃ using powder X-ray diffraction, magnetic and electrical resistance measurements. Nd doping induces a simultaneous transition on the structure, the magnetic order, and the electronic phase in La_0.83-xNd_xK_yMnO₃. It exhibits a rhombohedral-orthorhombic structural transition, a ferromagnetic-paramagnetic transition associated with a metal-insulator transition, and a low temperature magnetic transition antiferromagnetic-like associated with a low-temperature insulating state in La_0.83-xNd_xK_yMnO₃. Nd doping also results in the presentation of the second magnetoresistance ratio (MR) peak at low temperature. All these phenomena might be interpreted by Nd doping induced a phase separation between the ferromagnetic metallic state and the antiferromagnetic insulating state at low temperature

[en] The structural and magnetic properties of Ni₅₀Mn_25+xSb_25-x (0≤x≤18) Heusler alloys have been investigated by x-ray diffraction, magnetization, thermal expansion, and electrical resistivity measurements. Austenitic phases with the L2₁ cubic crystal cell and martensitic phases with Pmm2 orthorhombic structures have been observed at room temperature in alloys with 0≤x≤12.5 and 13≤x≤14, respectively. The Curie temperatures of the austenitic phases decrease linearly with increasing x and change from 370 (x = 0) to 340 K (x = 12.5). In the concentration 7< x≤10, the system is found to undergo martensitic phase transitions above 150 K. The martensitic transition temperatures increase rapidly with increasing x and for x≥13.5 the temperature exceeds the Curie temperature of the austenitic phase (340 K). The alloys in their martensitic phases exhibit complex magnetic behavior. The phase diagram with respect to temperature and composition of the Ni₅₀Mn_25+xSb_25-x system has been determined, where the following magnetic phases have been observed in the martensitic state: antiferromagnetic phase (14< x); paramagnetic and antiferromagnetic (13≤x≤14, above 120 K) mixed phase; ferromagnetic and antiferromagnetic (10≤x≤14, above 20 K) mixed phase. The mixed phases result in observation of the exchange bias effect at low temperatures (below 120 K)

[en] X-ray diffraction, magnetization, electrical resistivity and thermal expansion measurements were done on a series of Heusler alloys of the form Ni₂MnGa_1-xIn_x 0< x<0.25. X-ray diffraction patterns indicate that the samples possess a highly ordered Heusler alloy L 2₁ type structure. Due to the larger radii of the In ion, the lattice parameters were found to expand with increasing In concentration. The negative volume anomaly (∼ -0.1%) is found to accompany the martensitic transition. With increasing In content, a linear decrease of the martensitic transition and the Curie temperatures were observed. The compositional-transition temperature phase diagram is evaluated. Possible reasons for the structural transformations are discussed

[en] We have studied the crystal structure, the magnetic and electron transport properties and the magnetoresistance effect of nitrogenation of La_2/3Ca_1/3MnO₃ by x-ray powder diffraction, magnetic measurement and standard four-probe resistance-temperature measurement. Nitrogenation results in an increase in the lattice parameter and unit cell volume, and induces the formation of a superlattice. The N atom prefers to occupy the 4c crystal position in the superlattice structure. Nitrogenation weakens the ferromagnetic ordering and results in the decrease of Curie temperature and the saturation magnetic moment but increases the electrical resistivity significantly. The electrical resistivity exhibits a metal-insulator (MI) transition, but the MI transition temperature decreases after nitrogenation. The behaviour of the electrical resistivity follows the equation ρ=ρ₀(1-aT+bT²+cT⁴) in the metal regime. However, it follows the formula ρ=ρ₀exp (E/k_BT) in the insulator regime. The magnetoresistance ratio measurement shows an increase of 15% after nitrogenation. (author)

[en] We report on the variation of the magnetoresistance property of La_1-xSr_xMnO₃ whose Mn sites are doped with chromium and rhenium. Two different series of compounds of the formula La_0.7Sr_0.3Cr_yMn_1-yO₃ (y=0.05, 0.10, 0.15, 0.20, 0.30, 0.40 and 0.50) and La_1-xSr_xRe_0.10Mn_0.90O₃ (x=0.12, 0.20 and 0.30) are prepared. A detailed study has been carried out to determine the structural, magnetic and transport properties of the chromium and rhenium doped compounds using the x-ray diffraction, dc magnetic susceptibility, four probe method for electrical resistance and magnetoresistance measurement techniques. X-ray diffraction shows the formation of a homogeneous compound with the rhombohedral (R-3c space group) structure within the Cr concentration of 0.05< y<0.15 for the La_0.7Sr_0.3Cr_yMn_1-yO₃ and 0.12< x<0.30 for the La_1-xSr_xRe_0.10Mn_0.90O₃ compounds. The magnetization, magnetic transition temperature and the metal-insulator transition temperature decrease due to the Cr (Re) substitution. The magnetization curves broaden and the overall resistivity of the compounds increases with increasing Cr or decreasing Sr content except for the La_0.88Sr_0.12Re_0.10Mn_0.90O₃ compound, whose resistivity decreases and which shows metallic behaviour below the transition temperature. The resistivity and the magnetization show a scaling dependence on each other. It is shown that the variation in the magnetic and transport properties of the substituted compounds can be ascribed to a compositional dependence of the Mn³⁺-Mn⁴⁺ ferromagnetic interaction as a result of the antiferromagnetic interaction of Cr³⁺-O-Cr³⁺ ions and to the distortion of the crystal lattice. The magnetoresistance shows an increasing trend due to the increased resistivity of the compounds and is explained on the basis of percolation of the charge carriers through the ferromagnetic clusters present in the insulating antiferromagetic compounds and scattering effect at the grain boundaries. (author)

[en] A series of Fe doped Ni₂Mn_0.75-xFe_xCu_0.25Ga Heusler alloys have been investigated by means of x-ray diffraction, magnetizations, thermal expansion, and electrical resistivity measurements. In Ni₂Mn_0.75Cu_0.25Ga, martensitic and ferromagnetic transitions occur at the same temperature. Partial substitution of Mn by Fe results in a decrease of the martensitic transition temperature, T_M, and an increase of the ferromagnetic transition temperature, T_C, resulting in separation of the two transitions. In addition to the martensitic transition, complete thermoelastic intermartensitic transformations have been observed in the Fe doped Ni₂Mn_0.75-xFe_xCu_0.25Ga samples with x>0.04. An unusual transition is observed in the alloy with x = 0.04. The magnetization curve as a function of increasing temperature shows only one first-order transition in the temperature range 5-400 K, which is identified as a typical coupled magnetostructural martensitic transformation. The magnetization curve as a function of decreasing temperature shows three different transitions, which are characterized as the ferromagnetic transition, the martensitic transition and the intermartensitic transition.

[en] We have studied the structural and magnetic properties of Ni₂MnGa_1-xB_x Heusler alloys with 0≤x≤0.25 using x-ray diffraction, thermal expansion, electrical resistivity, and magnetization measurements. The magnetization measurements were made within the temperature interval of 5-400 K and at applied magnetic field of 0-5 T. The samples with low B concentrations (x<0.05) were found to be of the cubic L2₁ phase at 300 K. A martensitic phase along with the cubic L2₁ phase appears for x≥0.05, and the amount of the martensitic phase was found to increase with increasing x. The critical concentration of the boron substitution (within which Heusler phases exist) was found to be around x = 0.1. The cubic cell parameter was observed to decrease with increasing x in the interval 0≤x≤0.1. The alloys were ferromagnetically ordered at 5 K and the saturation magnetization (M_S) was found to decrease with increasing boron concentration. The Curie temperatures (T_C) and martensitic transition temperatures (T_M) for the alloys with 0≤x≤0.25 have been determined and a phase (T-x) diagram has been constructed. T_M increases rapidly and T_C decreases slowly with increasing B concentration in the interval 0≤x≤0.1. The dependence of the phase transition temperatures and magnetization on B concentration is discussed.