Search

The effects of annealing process and chemical pressure on the structural and magnetocaloric properties of CoMn1-xVxGe (x=0.05 and 0.10) alloys have been studied. Rietveld refinement of XRD patterns revealed that all samples are single phase and they crystallize in hexagonal structure with a space group (P6(3)/mmc) at room temperature. The structural phase transition temperature T-struct decreases with increasing vanadium (V) content drastically in compare to CoMnGe alloy which exhibit a first order structural transition at around 450 K. The decrease in T-struct. by substituting fourth element in CoMnGebased alloys are discussed in frame of changing its valence electron concentration (e/a) values. We found that, alloys exhibiting a first order magneto-structural transition (FOMT) around room temperature, have an e/a value of 6.62-6.67. The e/a dependence of the magnetostructural transition temperature can be used as a guide to obtain an alloy with FOMT around room temperature. (C) 2019 Elsevier B.V. All rights reserved.

We have studied the magnetic properties and magnetocaloric effect of ball milled CoMn0.95V0.05Ge alloy by means of temperature and field dependence of magnetisation measurements. CoMn0.95V0.05Ge nano-powders with different particle size distribution were prepared by varying the milling time for 4, 6 and 8 h. The atomic force microscopy (AFM) images showed that the average size of the particles decreases with increased milling time as expected. The nature of the magnetic phase transition has been determined by using Arrott plots, rescaled magnetic entropy change and power exponents of Δ S M . We found that the nature of the magnetic transition for nano powders has a second order nature, although their bulk counterpart with same composition exhibits a first order magnetostructural phase transition. The observed maximum magnetic entropy change for nano powders is, therefore, slightly lower than that of their bulk counterparts. However a 50 % increasing of relative cooling power for nano-powders is achieved. These results suggest that CoMn0.95V0.05Ge nano-powders could be a suitable candidate as working substance for magnetic cooling technology around room temperature.

The structural, electronic, and magnetic features of Co2Mn1−xAlxTi (0 ≤ x ≤ 0.6) Heusler alloys (HAs) have been systematically investigated by experimental techniques (X-ray powder diffraction, scanning electron microscopy, and magnetization measurements) and ab initio theoretical calculations. Whole alloys have cubic structures at room temperature and exhibit ferromagnetic properties. The Curie temperature of Co2Mn1−xAlxTi (x = 0) is approximately 790 K, which is compatible with other studies. By increasing Al content, the temperature dependence of magnetization trials has proved a linear diminishment on Curie temperature and saturation magnetization.

The effect of heat treatment on the structural, magnetic and magnetocaloric properties of Ni43Mn46In11 melt-spun ribbons was systematically investigated using X-ray powder diffraction (XRD), scanni...

The effect of Cu substitution on the martensitic transition and magnetocaloric properties of arc-melted Ni 50−x Cu x Mn 39 Sn 11 (x = 6 and 7) Heusler alloys are investigated by differential scanning calorimetry, X-ray powder diffraction, scanning electron microscopy and magnetic measurements. According to XRD patterns, while Ni 44 Cu 6 Mn 39 Sn 11 alloy exhibit orthorhombic structure, Ni 43 Cu 7 Mn 39 Sn 11 alloy crystallize cubic L2 1 structure at room temperature. The substitution of Cu for Ni leads to decreasing on the martensitic transition temperatures to lower values. The magnetic entropy changes calculated from M(T) curves, for avoiding hysteresis losses in the vicinity of the martensitic transition region, by using Maxwell relation. The maximum magnetic entropy change, Δ S M is found 11.0 J kg −1 K −1 for Ni 43 Cu 7 Mn 39 Sn 11 alloy around the martensitic transition region, which is nearly twice as large as the Ni 44 Cu 6 Mn 39 Sn 11 alloy under the magnetic field changing from 0 to 2 T.

The effects of Ti substitution for Mn and heat treatment on structural, magnetic, and magnetocaloric properties of CoMnGe alloy have been investigated using electron microscopy, X-ray diffraction, calorimetric, and magnetic measurements. According to X-ray diffraction measurements, CoMn1−x Ti x Ge alloys are in a single phase hexagonal structure at room temperature. It is found that the as-cast CoMn0.95Ti0.05Ge alloy shows a magnetostructural phase transition close to room temperature. The transition shows a large magnetic entropy change and a small hysteresis in the isothermal magnetic field-dependent magnetization measurements. After annealing, the phase transition temperature decreases slightly and the magnetization is sharply decreasing at Curie temperature. The sharp change of magnetization at phase transition temperature is accompanied by a significant increase in the magnetic entropy change, i.e., magnetic entropy change value for the magnetic field change of 1 T was increased from −3.3 to −6.3 J kg−1 K−1. Moreover, after annealing, hysteresis losses reduced significantly for ∆H = 7 T. Accordingly, the heat treatment has a significant effect on magnetocaloric properties of the CoMn0.95Ti0.05Ge alloy.

This paper presents the role of the conventional and Soliton wave model deposition at low substrate temperature (300–100 K) on the structural, electric and magnetic properties of Co35Fe65 thin films deposited by thermal evaporation using bulk polycrystalline Co35Fe65 alloy. On account of obtaining superior quality magnetic thin films without any high temperature growth processes or heat treatment, the Soliton wave growth model at suitable low temperature range is used. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques are employed to investigate the various structural properties. Morphological and structural analyses of entire 30 nm Co35Fe65 thin films deposited on Si (100) substrate reveal that the stoichiometry is preserved over the whole temperature deposition and BCC crystalline formed with (110) texture. To attain the electrical and magnetic properties, resistivity and vibrating-sample magnetometer (VSM) measurements are evaluated. Soliton wave model deposition significantly increased magnetic anisotropy constant K1 = 0.105 Merg/cm3, MR/MS = 0.83 and coercivity HC = 272 Oe at 300 K when the compared to conventional deposition range in this work (K1 = 0.014 Merg/cm3, MR/MS = 0.6 and HC = 50 Oe). Growth with novel approach of Co35Fe65 thin films highlights the reasonable low coercivity, the high saturation magnetization, the high magnetic anisotropy and the low electrical resistivity values, with tailored grain size, make them feasible to use in magnetic sensor technology in the near future.

In this work, we have studied on double-layered perovskite (Ruddlesden–Popper) manganite structure in Pr1.75Sr1.25Mn2O7 synthesised by sol–gel method. The crystal structure of the double-layered perovskite is found as tetragonal from the X-ray diffraction analysis with I4/mmm space group. A high Curie temperature, TC= 305 K is observed from the temperature dependence of magnetisation measurement. The isothermal magnetisation curves showed that magnetic phase transition is second order due to the positive slope of the Arrott plots. Maximum magnetic entropy change (?SM) and adiabatic temperature change (?Tad) values are calculated as 3.99 J kg-1 K-1 and 2.1 K under external magnetic field of 70 kOe, respectively. Since our double-layered perovskite manganite sample has desired TC value and relatively high ?SM, it can be a potential candidate as a magnetocaloric material for room temperature magnetic cooling systems. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

The magnetic and magnetocaloric properties of CoMn 0.9 Fe 0.1 Ge alloy has been investigated by using of electron microscopy, X-ray diffraction, calorimetric, heat capacity and magnetic measurements. The substitution of Fe atoms for Mn atoms in the CoMnGe system leads to a decrease in the martensitic transition temperature from 650 K to room temperature (RT) and presents the magnetostructural properties in vicinity of RT. In order to assess MCE, temperature dependent of magnetization measurements have performed under applying variable magnetic fields. The largest entropy change values are −34.9 J kg−1 K−1 (magnetization) and −33.6 J kg−1 K −1 (demagnetization) for Δ H = 5 T . The adiabatic temperature change value of CoMn 0.9 Fe 0.1 Ge is calculated 8.5 K for 2 T from magnetic and heat capacity measurements. The density of states of electrons at Fermi level and the Debye temperature values of this alloy are found 1.19 states eV−1 atom−1 and 353 K from low temperature heat capacity measurements. This giant magnetocaloric effect makes this material a very promising candidate for future RT cooling applications.

The effect of number of arachidic acid (AA) Langmuir layers and pH values on morphology and local electrical properties of polycrystalline cadmium sulphide (CdS) film was investigated by atomic force microscopy, electric force microscopy (EFM) and scanning Kelvin probe microscopy (SKPM). Atomic force microscopy (AFM) surface analysis showed the polycrystalline relief of CdS surface with the roughness value about 8.5 +/- 0.3 nm and the drastic increases up to 25 +/- 0.9 nm for semiconductor surface modified by 1, 3 and 5 AA Langmuir layers at both pH value (pH 3.6 and 8.6). Surface potential (SP) values were estimated by EFM method and showed the same sequence of changes and were equal to -1 V for CdS film and to 2.4 V and 3.5 V for 3 AA layers at pH 3.6 and 8.6, respectively. SP of 1 and 5 AA Langmuir layers was about 2 V at both pH values. Furthermore, the electrical characteristics and parameters of samples calculated by EFM quantitative method were compared with SKPM method. EFM analysis showed more pronounced SP value changes than SKPM measuring, due to mathematical value processing of the established Coulomb interaction between the probe and the sample surface.

In this study, magnetic and electromagnetic energy conversion of magnetocaloric materials (MCMs) and magnetic refrigeration, which is based on magnetocaloric effect (MCE), is presented in detail and made apprehensible. The MCE is defined as cooling or warming occurring in the magnetic material under adiabatic conditions when the external magnetic field is applied or removed from the magnetic material and vice versa. This result has been known as “adiabatic demagnetization” for years, though this phenomenon is a practical use of the MCE in magnetic materials. The magnetic materials demonstrate the MCE in the vicinity of their critical temperature. The magnetocaloric system is environmentally friendly and more efficient than conventional refrigeration cycle system based on vapor compression. Magnetic refrigeration is a cooling technology based on the MCE. This technique can be used to attain low temperatures, as well as the ranges used in common refrigerators. In magnetic and electromagnetic energy conversion, the coefficient of the performance (COP) for the system reaches 30–60% theoretical efficiency of the Carnot cycle. Magnetic refrigeration is being pursued using low magnetic fields near room temperature in hopes of enabling commercial devices using permanent magnets as the field source.

It was shown that the complex research of iron nanoparticles properties by different methods, supplemented each other, permit to receive the data about the interior sizes of nanoparticles, a number of physical properties of particles, their dependence on frequency and changes produced by various influences. It was found that the conductivity of nanoparticles changed under the square depen-dence σ = σoω2

The influence of Cu substitution for Mn on magnetic and magnetocaloric properties has been investigated in Ni 50 Mn 34− x Cu x In 16 ( x =1.3 and 1.6) Heusler alloys by using calorimetric and magnetic measurements. The temperature dependent magnetization measurements and calorimetric studies indicate that martensitic transition temperatures shift to higher temperatures with increasing valence electron concentrations, e / a . The isothermal magnetization curves around the martensitic transition temperatures show a typical metamagnetic behavior. Associated with that, large positive values of magnetic entropy changes around structural transition region were determined by using the Maxwell and Clausius–Clapeyron relations. The maximum magnetic entropy change values were found to be 25.2 and 5.7 J kg −1 K −1 for Ni 50 Mn 34− x Cu x In 16 ( x =1.3 and 1.6) alloys by Maxwell relation in a magnetic field change of 2 T. In order to understand the limit can be reached for, the magnetic entropy change values recalculated by Clausius–Clapeyron relation. Obtained maximum entropy change values are 22.8 and 16.3 J kg −1 K −1 for Ni 50 Mn 34− x Cu x In 16 ( x =1.3 and 1.6) alloys by Clausius–Clapeyron relation.

The magnetic and magnetocaloric properties of CoMnGe1−xGax (0.02 ⩽ x ⩽ 0.063) alloys have been investigated by using calorimetric, X-ray diffraction and magnetic measurements. Our results show that the structural and magnetic phase transitions in CoMnGe1−xGax alloys are tailored by the substitution of Ga for Ge. The CoMnGe1−xGax (x = 0.05, 0.055 and 0.06) alloys exhibit a giant magnetocaloric effect due to coexistence of magnetic and Martensitic phase transitions at the same temperatures. The entropy change values range from −3.2 to −38.4 J kg−1 K−1 for Δ H = 7 T and are proportional to the volume differences of the phases involved in the transition. The adiabatic temperature change value of CoMnGe0.945Ga0.055 is calculated as 6.5 K for the magnetic field change of 2 T from magnetic and heat capacity measurements. The density of states of electrons at Fermi level and the Debye temperature values of this alloy are found 1.37 states eV−1 atom−1 and 337 K from low temperature heat capacity measurements.

The magnetostructural and magnetocaloric properties of CoMnGe 1 − x Ga x B 0.015 ( x =0.05 and 0.06 are named Alloy-1 and Alloy-2, respectively) alloys have been investigated by X-ray powder diffraction, calorimetric and magnetization measurements. Both alloys have hexagonal structures at room temperature and show first order phase transition below room temperature. The entropy change- Δ S of these alloys are calculated as −22.1 J kg −1 K −1 (for Alloy-1 alloy) and −27.1 J kg −1 K −1 (for Alloy-2 alloy) under Δ H = 7 T . Magnetic hysteresis losses of these alloys are very small when compared with the undoped alloy. Considering the high magnetocaloric effect and low magnetic hysteresis features, boron doping on CoMnGe family alloys provides an alternative method to tailor magnetic and magnetocaloric properties.

We have carried out 55Mn and 145Nd NMR measurements on re-entrant ferromagnets La1−xNdxMn2Si2 (x = 0.35, 0.4). From the bulk magnetization measurements, the compound with x = 0.35 shows ferromagnetic properties in the temperature range from T C inter = 305 to T N inter = 165 K , and antiferromagnetic properties down to ∼65 K. Then the compound orders ferromagnetically below T C Nd = 65 K . A similar temperature dependence of magnetization is observed for x = 0.4. The 55Mn NMR frequencies of both compounds fall into range 160–163 MHz at 1.4 K and are about 166 MHz at 77 K without external magnetic field. The temperature dependence of resonance frequency has been measured for x = 0.35 in the temperature from 1.4 K up to 88 K. The frequency of 55Mn is almost independent of temperature in the ferromagnetic state within experimental error, and increases abruptly around 65 K corresponding to the transition between ferromagnetic and antiferromagnetic states. The Mn magnetic moment at 1.4 K is estimated to be 2.3μB in comparison with the results of neutron diffraction measurements. Zero-field 145Nd NMR have been observed at 415 MHz at 1.4 K for both compounds. Nd magnetic moments in La1−xNdxMn2Si2 (x = 0.35, 0.4) are estimated to be 2.3μB from hyperfine field analysis.

The magnetic properties of La1-xNdxMn2Si2 (x = 0.30-0.45) compounds are studied over the temperature range 5 K

We report the preparation and characterization of spherical core-shell structured Fe3O4-Au magnetic nanoparticles, modified with two component self-assembled monolayers (SAMs) consisting of 3-mercaptophenylboronic acid (3-MBA) and 1-decanethiol (1-DT). The rapid and room temperature synthesis of magnetic nanoparticles was achieved using the hydroxylamine reduction of HAuCl4 on the surface of ethylenediaminetetraacetic acid (EDTA)-immobilized iron (magnetite Fe3O4) nanoparticles in the presence of an aqueous solution of hexadecyltrimetylammonium bromide (CTAB) as a dispersant. The reduction of gold on the surface of Fe3O4 nanoparticles exhibits a uniform, highly stable, and narrow particle size distribution of Fe3O4-Au nanoparticles with an average diameter of 9 +/- 2 nm. The saturation magnetization value for the resulting nanoparticles was found to be 15 emu/g at 298 K. Subsequent surface modification with SAMs against glucoside moieties on the surface of bacteria provided effective magnetic separation. Comparison of the bacteria capturing efficiency, by means of different molecular recognition agents 3-MBA, 1-DT and the mixed monolayer of 3-MBA and 1-DT was presented. The best capturing efficiency of E. coli was achieved with the mixed monolayer of 3-MBA and 1-DT-modified nanoparticles. Molecular specificity and selectivity were also demonstrated by comparing the surface-enhanced Raman scattering (SERS) spectrum of E. coli-nanoparticle conjugates with bacterial growth media.

Structural, magnetic and magnetocaloric properties of arc-melted polycrystalline Ni43Mn46 xAlxIn11 (x = 0, 0.5 and 1.0) alloys have been investigated by X-ray powder diffraction, scanning electron microscope and magnetic measurements. It is found that all investigated alloys undergo a first-order structural phase transition from austenite (cubic) to martensite (tetragonal) structure on cooling. According to temperature dependent magnetization measurements, the martensitic and magnetic phase transition temperatures decrease by substituting small amounts of Al for Mn in Ni43Mn46In11 alloy. Inverse magnetic entropy changes and relative cooling power (RCP) values are found 5.10, 9.63, 11.42 J kg (1) K (1) and 57.4, 60.67, 65.04 J kg (1) for x = 0, 0.5 and 1.0 alloys for a magnetic field change of 2 T, respectively. (C) 2017 Elsevier B.V. All rights reserved.

The effect of Cu alloying on the structural, magnetic, and magnetocaloric properties of the Mn-rich Ni43Mn46−x Cu x In11 (x = 0, 0.9, 1.3 and 2.3) alloys was investigated with scanning electron microscopy, X-ray powder diffraction (XRD), and magnetization measurements. The substitution of Cu for Mn efficiently reduces the structural and magnetic transition temperatures of the Ni43Mn46In11 alloy. As a result, while the XRD pattern of the Ni43Mn46In11 alloy shows only tetragonal structure, the structures of Cu-doped alloys consist of both cubic and tetragonal phases at room temperature. The positive magnetic entropy changes (ΔS M) in the alloys were determined from the magnetic field-dependent magnetization measurements-M(H) using the Maxwell relation. Around the structural transition region, a maximum ΔS M was found 21.08 J kg−1 K−1 for the Ni43Mn46−x Cu x In11 (x = 2.3) alloy in a magnetic field change of 18 kOe.

Magnetocaloric and magnetoresistance properties of SmMn2−xFexGe2 (x=0.05 and 0.10) and SmMn2−xCoxGe2 (x=0.05 and 0.15) compounds have been studied by magnetic and resistance measurements in the temperature range between 30 and 350 K. All compounds exhibit metamagnetic transition from antiferromagnetism to ferromagnetism around the Sm moments ferromagnetic ordering temperature-TSm and Mn moments antiferromagnetic ordering temperature-TN1. The magnetic entropy changes of these compounds are estimated from the Maxwell equation, Maxwell Clausius Clapeyron equation, Landau theory and mean-field theory. The maximum magnetic entropy change values of SmMn1.90Fe0.10Ge2 and SmMn1.85Co0.15Ge2 compounds are −8.1 J kg−1 K−1 and −5.1 J kg−1 K−1 in a magnetic field change of 5 T, respectively. These compounds show negative magnetoresistance around the magnetic phase transition temperatures. The magnetoresistance value of SmMn1.95Fe0.05Ge2 is −23% at TSm which is bigger than the magnetoresistance value of SmMn2Ge2 (−15%).

We study magnetothermal properties of the La0.775Gd0.225Mn2Si2 compound. The magnetic contribution to the heat capacity is estimated by zero-field and 0.5 T magnetic field data. According to Arrott plot, the La0.775Gd0.225Mn2Si2 has a second order transition at a Curie temperature (TC) and a first order transition at a lower temperature. The λ-type peak in the heat capacity data also confirms the second order transition at the Curie temperature. We determined the electronic, magnetic and lattice contributions to the heat capacity. In addition, Debye temperature and N(EF) are estimated by heat capacity data as a function of temperature under zero and 0.5 T magnetic field.

Evolution of magnetocaloric effect (MCE) of nanostructured CoMnGe0.95Ga0.05 powders has been investigated by electron microscopy (SEM), X-ray powder diffraction (XRD), thermal (DSC) and magnetization measurements. The nanostructured powders are composed of very fine grains (7 +/- 2 and 35 +/- 2 nm) obtained from Rietveld refinements. The nanostructured powders show the unique ferromagnetic martensite-paramagnetic austenite transition around the room temperature like the bulk alloy. Furthermore, while the martensitic transition occurs in narrow temperature for bulk alloy, it occurs in broad temperature range for the nanostructured powders. The isothermal magnetic entropy change values -Delta S-M are estimated from the isothermal magnetization curves. The maximum Delta S-M values of 5 h milled nanopowders are -7.2 and -21.5 J kg(-1) K-1 for a magnetic field change of 2 and 7 T, respectively. The magnitudes of the MCE, magnetic and thermal hysteresis values of nanostructured powders are smaller than those of bulk alloy. Our findings offer the nanostructured CoMnGe0.95Ga0.05 powders for the promising applications in magnetic refrigeration. (C) 2012 Elsevier B. V. All rights reserved.

The structure,magnetic and magnetocaloric properties of the Ge-rich Gd5Ge2.05-xSi1.95-xMn2x (x=0.01 and 0.03) alloys were investigated by scanning electron microscopy,X-ray powder diffraction,differential scanning calorimeter (DSC) and magnetization measurements.The results of energy dispersive X-ray analysis (EDX) and X-ray diffraction analyses showed that the composition and crystal structure of the alloys were desired.DSC measurements were performed to determine the transformation temperatures for each alloy.Both alloys exhibited the first order phase transition around room temperature.The alloys showed an anti-ferromagnetic transition around 60 K.The isothermal magnetic entropy changes of the alloys were determined from the isothermal magnetization measurements by using the Maxwell relation.The maximum values of isothermal magnetic entropy change of the Gd5Ge2.05-xSi1.95-xMn2x alloy with x=0.01 was found to be -12.1 and -19.8 J/(kg·K) using Maxwell equation around 268 K in applied fields of 2 and 5 T,respectively.

The magnetic structures of the La 0.65 Nd 0.35 Mn 2 Si 2 have been investigated by powder neutron diffraction between 5 and 350 K. According to magnetic measurements this compound shows multiple magnetic phase transitions. Neutron diffraction indicates a canted ferromagnetic structure above 220 and below 46 K. Between 50 ≤ T ≤ 70 K there is a mixed phase where canted ferromagnetic and antiferromagnetic structure coexist. Moreover, La 0.65 Nd 0.35 Mn 2 Si 2 has a two-step magnetic transition from an antiferromagnetic to ferromagnetic state between 65 and 22 K. This two-step transition had not been observed so far and in this study it is studied in depth.

The thermal and magnetothermal properties of La0.5Pr0.5Mn2Si2 and isostructural LaFe2Si2 intermetallic compounds in the temperature range 4.5–303 K are reported with and without applied magnetic field. The electronic, lattice, and magnetic contributions to the heat capacity of La0.5Pr0.5Mn2Si2 are determined and analyzed. We have determined T C i n t e r and T N i n t e r from heat capacity experiments; the values are in line with those from the magnetization measurements. We conclude that in order to observe the anomaly in the heat capacity data around T N i n t e r in the R 1 − x R x ′ Mn 2 Si 2 system, the transition around T N i n t e r should occur in a narrow temperature interval.

The preparation and application of rod-shaped core-shell structured Fe(3)O(4)-Au nanoparticles for immunomagnetic separation and sensing were described for the first time with this study. To synthesize magnetic gold nanorod particles, the seed-mediated synthetic method was carried out and the resulting nanoparticles were characterized with transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-Vis), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). Magnetic properties of the nanoparticles were also examined. Characterization of the magnetic gold nanorod particles has proven that the resulting nanoparticles were composed of Fe(3)O(4) core and the gold shell. The rod-shaped gold-coated iron nanoparticles have an average diameter of 16 +/- A 2 nm and an average length of about 50 +/- A 5 nm (corresponding aspect ratio of 3). The saturation magnetization value for the magnetic gold nanorod particles was found to be 37 emu/g at 300 K. Rapid and room temperature reaction synthesis of magnetic gold nanorod particles and subsequent surface modification with E. coli antibodies provide immunomagnetic separation and SERS application. The analytical performance of the SERS-based homogenous sandwich immunoassay system with respect to linear range, detection limit, and response time is also presented.

The effect of the substitution of Cu for Ni on the magnetoresistance behaviour and the magnetocaloric properties of the Ni 50 Mn 34 In 16 alloy has been investigated. The (Ni–Cu) 50 Mn 34 In 16 alloys crystallize in the cubic L2 1 structure in austenite phase. While the M s temperature is about 160 K for the Ni 47.5 Cu 2.6 Mn 34.0 In 15.9 alloy, the martensitic transition is not observed for Ni 45.5 Cu 4.6 Mn 33.8 In 16.1 alloy. To estimate the magnetic entropy change of the Ni 47.5 Cu 2.6 Mn 34.0 In 15.9 alloy, the magnetization measurements as function of magnetic field are performed by continuous and noncontinuous heating methods. The Ni 47.5 Cu 2.6 Mn 34.0 In 15.9 alloy shows the magnetostructural transition whose irreversible ratio is about 50% at 160 K. The magnetocaloric effect strongly depends on the sample history due to the occurrence of the irreversible magnetostructural transition. For the magnetic field change of 2 T, giant magnetoresistance value is about −68% that is rather big among the similar bulk alloys.

Influence of irreversibility (magnetoplasticity) on inverse magnetocaloric effect and magnetoresistance of the (Ni,Cu) 50 Mn 36 Sn 14 alloys has been investigated by magnetization and resistivity measurements. X-ray powder diffraction patterns indicate that all alloys crystallize in L2 1 cubic structure at room temperature. The substitution of Cu for Ni leads to decreasing on the martensitic transition temperature and increasing on the Curie temperature. The magnetic field dependence of magnetization measurements is performed with continuous heating and noncontinuous heating methods to find the influence of irreversibility on magnetocaloric effect. It is observed that the magnetic entropy change depends strongly on magnetization measurement methods. The resistivity measurements show that the (Ni,Cu) 50 Mn 36 Sn 14 alloys have the one-way magnetostructural transition. Magnetoresistance about −46% is observed at magnetostructural transition temperatures.

We have studied the magnetothermal properties of La0.8Sm0.2Mn2Si2. The magnetic contribution to the heat capacity has been estimated by using the zero-field and 1 T magnetic field data. According to Arrott plots, the La0.8Sm0.2Mn2Si2 has second order transition at Curie temperature. The λ -type peak in the heat capacity data also confirms the second order transition at the Curie temperature. The electronic, magnetic and lattice contributions to the heat capacity of this compound are determined and analyzed. Moreover, the Debye temperature and N ( E F ) have been estimated by using the heat capacity data under zero and 1 T magnetic fields. The ΔSM(T) curve from heat capacity is in very good agreement with that from Maxwell relation.

The influence of the manganese-alloying on the structure and magnetocaloric properties of the Gd5Si2.05Ge1.95 compound was studied by X-ray powder diffraction and magnetization measurements. The Gd5Si2.05–xGe1.95–xMn2x (2x=0, 0.03 and 0.08) compounds crystallized in the Gd5Si2Ge2-type monoclinic structure. In all X-ray powder diffraction patterns, a minor hexagonal Gd5Si3 phase was observed as a second phase. With increasing Mn content, the unit cell volume increased. For the compounds with x=0, 0.03 and 0.08, the first order phase transition was observed. The maximum isothermal magnetic entropy change of the Gd5Si2.05–xGe1.95–xMn2x compound with 2x=0.03 at 275 K was found to be −11.6 J/(kg·K) in an applied field of 5 T.

The La 1− x Ce x Mn 2 Si 2 compounds ( x =0.35 and 0.45) exhibit an antiferromagnetic–ferromagnetic transition caused by the changes in distance between Mn atoms due to temperature changes. A field-induced transition from antiferromagnetic state to ferromagnetic state at a critical field, which decreases with increase in temperature, can also be induced by applying a magnetic field. In this paper our aim is to study the magnetization and magnetocaloric effect, close to transition temperatures. Our subsidiary aim is to examine the temperature dependence of critical field and ferromagnetic fraction of compounds. The variation of magnetocaloric effect with temperature is correlated with the ferromagnetic–antiferromagnetic phase coexistence. Our final aim is to examine the harmony between magnetocaloric effect values calculated both by the Maxwell theory and by the Landau theory.

Nanocrystalline LaMn 2 Si 2 powders have been obtained by high-energy ball milling for 30 min from bulk alloys. After milling a high coercivity about 6 kOe is observed at 10 K in contrast to neglectable coercivity for the bulk LaMn 2 Si 2 at 5 K. The average grain size of the optimum particles which is obtained from X-ray diffraction pattern and HRTEM picture is about 20 nm. The magnetic hardening is observed for the nanocrystalline LaMn 2 Si 2, reflected in the coercivity field strength of 6 kOe at 10 K.

Intermetallic compounds of HoMn6−xFexSn6 (0 ≤ x ≤ 1.2) were studied by means of field-cooled (FC) and zero-field-cooled (ZFC) magnetization measurements in the temperature range 5 K ≤ T ≤ 600 K. The unit cell parameters decrease with the increasing of Fe content. The compounds with x = 0 and 0.3 behave ferrimagnetically in the whole temperature range and spin reorientation transition is observed at 200 and 185 K, respectively. The x = 0.5 and 0.6 compounds show ferrimagnetic–helimagnetic–ferrimagnetic phase transitions with decreasing temperature while the compounds with x = 0.9 and 1.2 only show helimagnetic–ferrimagnetic phase transitions. Additionally, for the x = 0.6 compound the metamagnetic phase transition from helimagnetism to ferrimagnetism is induced by an applied field 20 kOe.

We have studied the effects of Co substitution for Mn on the structure and magnetic properties of the HoMn 6− x Co x Sn 6 compounds (0⩽ x ⩽0.25) with HfFe 6 Ge 6 -type structure (space group P6/mmm) by X-ray powder diffraction and magnetization measurements. A monotonic decrease of the lattice parameters a and c is observed with increasing Co content. While the compounds with x =0 and 0.05 exhibit ferrimagnetism in the whole temperature range, the compounds with 0.1⩽ x ⩽0.15 show ferrimagnetism, helimagnetism and re-entrant ferrimagnetism with decreasing temperature. For the compounds with x =0 and 0.05, the spin reorientation temperature is observed. A metamagnetic transition from helimagnetic magnetic ordering to ferrimagnetism is observed for the compounds with x =0.1 and 0.2. The results are summarized in the HoMn 6− x Co x Sn 6 magnetic phase diagram.

The magnetic structures of the La 1 - x Pr x Mn 2 Si 2 ( x = 0.4 , 0.7 and 1) have been investigated by powder neutron diffraction between 2 and 308 K. According to magnetic measurements, the x = 0.4 sample shows a typical SmMn 2 Ge 2 -like magnetic behavior. Neutron diffraction indicates a canted antiferromagnetic structure below 130 K and a canted ferromagnetic structure above 240 K. Between 130 and 240 K, the canted ferromagnetic and antiferromagnetic structures coexist. Since the magnetic moments of Mn atoms, the unit cell parameters and the scale parameters of the canted antiferromagnetism and canted ferromagnetism are highly correlated between 130 and 240 K, a special refinement procedure was introduced. The critical Mn–Mn value was determined as 2.87 A ˚ , and the spontaneous volume change and linear magnetostriction are derived. Neutron diffraction revealed a canted antiferromagnetic structure for La 0.3 Pr 0.7 Mn 2 Si 2 . A canted antiferromagnetic structure was also detected for PrMn 2 Si 2 by neutron diffraction in contrast to previous reports of a collinear arrangement. The present results are compiled together with previous ones on RMn 2 Ge 2 and RMn 2 Si 2 (R: Y, La and rare-earth) compounds in two magnetic phase diagrams. These two graphics summarize the general magnetic behavior of Mn in the RMn 2 Ge 2 and RMn 2 Si 2 compounds.

We have investigated the magnetic properties of R x R 1 - x ′ Mn 2 X 2 (X: Si, Ge) for various combinations of rare-earth elements R and R ′ by examining the evolution of the features in the temperature dependence of the low-field magnetization. By making use of the known magnetic structure of the parent compositions x = 0 and 1, the results of low-field magnetization measurements are interpreted for intermediate compositions to give information on their magnetic structure. We find antiferromagnetic–ferromagnetic (AF–FM) transitions, whereby the transition can be sharp or evolve over a considerable temperature range. We examine the magnetic transition temperatures as a function of the tetragonal unit cell parameter a and find that the critical spacings associated with interlayer AF–FM transitions are different in the silicides and germanides.

In the ongoing search for magnetocaloric materials, Heusler compound based ferromagnetic shape memory alloys (FSMA) of the system Ni-Mn-Z (Z=Sb, Ga, In, Sn) turned out to be very promising due to low cost of the containing elements and sizable magnetocaloric effects (MCE).[1] Substitution of Ni against Co in Ni-Mn-Z is known to improve the metamagnetic behavior of the martensitic transition, and thus the magnetocaloric properties as it increases the austenite Curie temperature T C A and leads to a transition from weak magnetic martensite to ferromagnetic austenite. Off-stoi-chiometric Ni-Mn-Al also shows a martensitic transition but accompanied by only small changes in the magnetization and hence neglectable MCE.[2] Substitution of up to 10at.% Co for Ni strongly promotes the ferromagnetism in the austenite phase and leads to a metamagnetic martensitic transition.[3] The magnetization difference between austenite and martensite enables magnetic field induced reverse transition together with an inverse magnetocaloric effect.[4,5]

We have investigated the magnetic structures and phase transitions of PrMn2−xFexGe2 (0 ≤ x ≤ 1) by the temperature dependence of weak-field magnetization and powder neutron diffraction. For the x = 0.6 sample, a typical SmMn2Ge2-like magnetic behavior is observed. The magnetic structures of the samples with x = 0.6, 0.8 and 1 have been determined between 1.5 and 305 K. Above T C inter (x = 0.6) and T N inter (x = 0.8 and 1) up to T N inter , these samples exhibit an intralayer antiferromagnetic structure in (0 0 1) Mn planes. For x = 0.6 sample, the magnetic structure is canted ferromagnetic along the c-axis between T N inter and T C inter and below T C Pr . For the samples with x = 0.8 and 1, the magnetic structure is canted antiferromagnetic along the c-axis below T N inter . Pr moments order ferromagnetically along the c-axis for the x = 0.6 sample below T C Pr . The results are summarized in the PrMn2−xFexGe2 magnetic phase diagram. The general magnetic phase diagram for RMn2−xFexGe2 (R: La, Ce, Pr, Nd and Sm) is also constructed from previous and present works. For these compounds, the magnetic phase transition from ferromagnetic to antiferromagnetic occurs at different intralayer Mn–Mn distances for each system. These critical distances are larger than the corresponding threshold value d Mn – Mn a = 2.87 A for the ternary end-member RMn2X2 compounds.

The magnetic properties of the HfFe 6 Ge 6 -type Gd 1 − x Tm x Mn 6 Sn 6 (0 ≤ x ≤ 0.9) compounds have been investigated in the temperature range of 5–600 K. The compounds with x ≤ 0.8 are ferrimagnetic in the whole temperature range. The ferrimagnetic Curie temperatures decrease with increasing Tm content from 435 K ( x = 0) to 344 K ( x = 0.9). The samples with x = 0.85 and 0.9 show paramagnetic–ferrimagnetic–antiferromagnetic–ferrimagnetic phase transitions with decreasing temperature. For the x = 0.85 compound, the metamagnetic phase transition from antiferromagnetism to ferrimagnetism is induced by an applied field 20 kOe.

The magnetic properties of Ce 1−xTbxMn2Ge2 ( 0 ⩽ x ⩽ 1 ) were investigated by means of field-cooled and zero-field-cooled magnetization measurements in the temperature range 5 K ⩽ T ⩽ 600 K . Earlier neutron diffraction experiments showed that Tb orders below 100 K while Ce does not order at any temperature. The substitution of Tb for Ce leads to a linear decrease in the lattice constants, and the magnetic interactions in the Mn sublattice cross over from a ferromagnetic character to an antiferromagnetic one. At low temperatures, the Tb sublattice also orders and reconfigures the ordering in the Mn sublattice. The results are collected in a phase diagram.

The magnetic properties of SmMn 2− x Co x Ge 2 (0 ≤ x ≤ 0.4) were studied by field-cooled and zero-field-cooled (ZFC) magnetization measurements in the temperature range 5 K ≤ T ≤ 350 K in low external field (50 Oe). Substitution of Co for Mn leads to a linear decrease in the lattice constants a and c , c / a and the unit cell volume V . Co substitution strongly changed the magnetic properties and the magnetic interactions in the Mn sublattice cross over from a ferromagnetic character to an antiferromagnetic one. The results of earlier neutron diffraction, Mossbauer spectroscopy and specific heat measurements on SmMn 2 Ge 2 are also used for interpreting the magnetization data and to give an account of the competing effects between various magnetic structures in the Mn and Sm sublattices.

The structure and magnetic properties of NdMn 2-x CU x Si 2 (0.2 ≤ x ≤ 1) were studied by X-ray powder diffraction and magnetization measurements. In this study, we investigate the variations in the magnetic properties of NdMn 2-x Cu x Si 2 as a function of Cu concentration by examing the evolution of the features in the temperature dependence of the magnetization. Earlier neutron diffraction experiments showed that the ferromagnetic Mn planes are ordered antiparallel along the c-axis below 380 K and the Nd sublattice orders at 33 K in NdMn 2 Si 2 . The ordering of the Nd sublattice reconfigures the ordering in Mn sublattice and leads to ferromagnetic ordering. With increasing amount of Cu, the Curie temperature has a maximum value of 120 K at x = 0.7 and decreases for the samples with x ≥ 0.8.

The structures and magnetic properties of Ce 1− x Gd x Mn 2 Si 2 and Pr 1− x Gd x Mn 2 Si 2 (0.2 ≤ x ≤ 0.8) were studied by X-ray powder diffraction and dc magnetization measurements. All compounds crystallize in the ThCr 2 Si 2 -type structure with space group I4/mmm . Substitution of Ce or Pr for Gd leads to a linear increase in the lattice constants and the unit cell volume. Below the Curie temperature T C Gd , the Gd sublattice orders and reconfigures the ordering of the Mn sublattice in Ce 1− x Gd x Mn 2 Si 2 and Pr 1− x Gd x Mn 2 Si 2 . With increasing concentration of Ce or Pr, T C Gd decreases in both compounds. Below T C Gd in Pr 1− x Gd x Mn 2 Si 2 , we observed a phase transition temperature as in Nd 0.6 Gd 0.4 Mn 2 Si 2 . The results for both systems are summarized in a preliminary magnetic phase diagram.

The magnetic properties of PrMn2−xCuxSi2 () were studied by field-cooled and zero-field-cooled magnetization measurements in the temperature range 5 K K in low external fields (5 mT) and by magnetic-field-dependent magnetization measurements in fields up to 5.5 T. Substitution of Cu for Mn leads to a linear decrease in the lattice constant c and the unit cell volume V and a linear increase in the lattice constant a. Earlier neutron diffraction experiments showed that Pr does not order down to 1.6 K in PrMn2Si2 while the ferromagnetic Mn planes are ordered antiparallel along the c axis. With the increasing Cu content, the magnetization increases rapidly at low temperatures for the samples with . Cu substitution strongly changes the magnetic properties and leads to the magnetic ordering of the Pr sublattice. This is mainly deduced from the discussion of the values of the magnetic moments at low temperatures. Below the Curie temperatures TC, the spins in the Mn sublattice are arranged parallel to the Pr sublattice. With increasing Cu, TC(x) has a maximum value of 155 K at x = 0.6 and decreases for samples with .

The crystal structure and magnetic properties of CeMn2−xFexGe2 (0≤x≤1.0) were studied by X-ray powder diffraction and DC magnetization measurements. All the compounds crystallize in ThCr2Si2-type structure. Substitution of Fe for Mn led to a decrease in the unit cell parameters and the unit-cell volume, whereas c/a exhibits parabolic variations. For the samples with x=0.625 and 0.65, the SmMn2Ge2-like magnetic behavior was observed. The results of earlier neutron and Mossbauer studies in CeMn2Ge2 were also used for interpreting the magnetization data and to give an account of the competing effects between various magnetic structures in the Mn sublattice. The results are summarized in a preliminary magnetic phase diagram.

The structure and magnetic properties of Nd 1− x Er x Mn 2 Ge 2 (0.0⩽ x ⩽1) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr 2 Si 2 -type structure with space group I 4/ mmm . Substitution of Er for Nd led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Er for Nd in NdMn 2 Ge 2 shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering. A typical SmMn 2 Ge 2 -like behaviour is observed for the x =0.4 sample. The results are summarized in α preliminary magnetic phase diagram.

The structure and magnetic properties of Nd 1− x Y x Mn 2 Ge 2 (0.0≤ x ≤0.6) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr 2 Si 2 -type structure with space group I4 / mmm . Substitution of Y for Mn led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Y for Nd in NdMn 2 Ge 2 shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering.

The magnetic structures of PrMn2−xCoxGe2 (x = 0.4, 0.5 and 0.8) with ThCr2Si2-type structure have been investigated by means of neutron diffraction measurements between 2 and 312 K. We introduced a new refinement procedure to determine the magnetic moments of Pr and Mn sublattices below the rare-earth ordering temperature TCPr because of the overlapping of the magnetic reflections of the Pr and Mn sublattices. Rietveld refinements demonstrated that above the Curie temperature an intralayer antiferromagnetic ordering within (001) Mn layers is observed in PrMn1.6Co0.4Ge2 and PrMn1.5Co0.5Ge2, while the intralayer antiferromagnetic ordering within (001) Mn layers is found over the whole temperature range for PrMn1.2Co0.8Ge2. Below the Curie temperature the PrMn1.6Co0.4Ge2 and PrMn1.5Co0.5Ge2 compounds have a canted ferromagnetic structure with the canting angles 62° and 65° at 2 K, respectively. Below 75 and 70 K, a ferromagnetic ordering of the Pr sublattice is observed along the c-axis for these compounds. Below 70 K, a ferromagnetic ordering of Pr sublattices is found (not detected by magnetic measurements) along the c-axis in PrMn1.2Co0.8Ge2.

The structural and magnetic properties of Pr1−xGdxMn2Ge2 were studied by x-ray diffraction and magnetization measurements. The substitution of Gd for Pr leads to a linear decrease in the lattice constants and the magnetic interactions in the Mn sublattice cross over from a ferromagnetic character to an antiferromagnetic one. At low temperatures, the rare-earth sublattice also orders and reconfigures the ordering in the Mn sublattice. The spins in the Mn sublattice are arranged parallel to the Pr sublattice and antiparallel to the Gd sublattice. The results are collected in a phase diagram.