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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.

The magnetic properties, martensitic transformation characteristics, the magnetic field-induced transformation characteristics, and super spin-glass behaviour at low temperature of Ni46.86Co2.91Mn38.17Sn12.06 (at%) magnetic shape memory alloys (MSMAs) were investigated under various magnetic field levels over temperature intervals from 400 K to 10 K. We observe a small magnetization difference during the martensitic transition evidenced with a visible thermal hysteresis. To investigate the magnetic field induced phase fraction, the minimum magnetic field required to start and complete the magnetostructural phase transition is computed. Super-spin glass features in magnetic data are observed that interacting magnetic clusters are frozen below a critical temperature. Magnetization is computed as a function of temperature at various constant fields using molecular field theory. The critical exponent, β is deduced for the temperature-induced magnetization, which indicates that the MSMA exhibited ferromagnetic ordering during field-cooling and on heating an antiferromagnetic ordering at low temperatures and in low applied magnetic fields. These observations are consistent within the framework of an Ising or Heisenberg model.

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.

La0.5Pr0.5Mn2Si2 undergoes an antiferromagnetic-ferromagnetic transition at about 250 K (C). This transition can also be induced by an external magnetic field leading to a metamagnetic transition. This can lead to a large change in the magnetic entropy, which is useful for magnetic cooling and studying the magnetocaloric effect. We investigated the details of the spin configuration as the magnetic ordering progresses from AF to FM by neutron diffraction techniques under magnetic fields up to 5 T and using spectral refining methods. (C) The Minerals, Metals & Materials Society and ASM International 2017

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.

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.

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.

A simple, controlled and reproducible procedure is reported to obtain polymerized methylmethacrylate by embedding monodisperse Fe 60 Pt 40 nanoparticles. The magnetic properties of the composite material can be controlled by the magnetic properties and the concentration (up to 0.3 wt%) of the starting nanoparticle dispersions. SQUID magnetometry measurements of FePt-doped methylmethacrylate polymers show superparamagnetic behavior at room temperature confirming the homogeneous particle distribution and the non-occurrence of agglomerates inside the polymeric matrix also observed by transmission electron microscopy. Even at the highest concentration the average particle distances are so large that no particle interactions play a role.

The structure and the magnetic properties of ErCo 10 Mo 2− x Si x (0 ≤ x ≤ 2) compounds have been investigated by means of X-ray powder diffraction and magnetization measurements in the temperature range of 5–800 K. Substitution of Si for Mo led to a linear decrease in the lattice constants and the unit-cell volume. With increasing Si content the Curie temperatures shifted from 425 K ( x = 0) to 719 K ( x = 2). For the temperature range 5–350 K magnetization measurements were carried out in an applied magnetic field of 50 Oe. The spin reorientation temperature decreased from 139 K to 74 K as the Si content was increased from x = 0 to 1.5. No spin reorientation was observed for x = 0.5 and 2. Below the spin reorientation temperature, the compounds exhibit ferrimagnetic ordering.

We have studied the effects of replacing the stabilizing element Mo by V on the magnetic characteristics of the ErCo 10 Mo 2 − x V x family of compounds using magnetization measurements. The replacement was carried out progressively from x = 0 to x = 2 in steps of 0.5. X-ray powder diffraction analysis of the prepared samples showed that the expected ThMn 12 -type structure was obtained overwhelmingly with negligible amounts of secondary phases. The Curie temperatures showed no clear change of the replacement of Mo by V. Spin reorientation temperatures were observed to shift considerably to higher temperatures with increasing V content.

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 Dy(Mn1−xCox)Sn6 were studied by field-cooled and zero-field-cooled magnetization measurements in the temperature range 5 K⩽T⩽600 K in low external fields and by magnetic field-dependent magnetization measurements in fields up to 50 kOe. The temperature variation of the ferrimagnetic spin configuration of the compound with x = 0 , determined from earlier neutron diffraction experiments, was taken as the basis for the interpretation of the present data. We find that the overall magnetization at all temperatures and the ferrimagnetic Curie temperatures decrease with increasing Co content. Furthermore, the addition of Co leads to an initial increase in the coercivity at low temperatures up to x = 0.11 , after which it decreases.

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.

The various magnetic structures of the ThCr 2 Si 2 structured RMn 2 Ge 2 (R: rare-earth) compounds can lead to numerous magnetic configurations by gradually substituting the rare-earth element by another lanthanide. In this study, the magnetic properties of Nd 1− x Dy x Mn 2 Ge 2 (0⩽ x ⩽1) compounds were investigated by means of temperature-dependent DC magnetization measurements in low external magnetic fields. The substitution of Dy for Nd 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 orders in various configurations that depend on the composition. The results are collected in a phase diagram.

Theoretical and experimental issues connected with exchange-bias and exchange-spring behaviour are briefly reviewed, and the potential of conversion electron Mossbauer spectroscopy, including the 57Fe probe layer technique, to reveal the spin structure in layered systems is emphasized. First experimental results are reported for the new exchange-bias system FeSn2/Fe and for the exchange-spring system Sm–Co/Fe.

The structural and magnetic properties of PrMn 2− x Cr x Ge 2 (0⩽ x ⩽1.0) were studied by X-ray diffraction and magnetization measurements. The powder samples crystallize in the ThCr 2 Si 2 -type structure, and the lattice constants at room temperature show almost no variation as Cr substitutes Mn. The observed phase transitions are summarized in a proposed magnetic x − T phase diagram and compared with previous Moessbauer spectroscopy and neutron diffraction results for x =0.

The magnetic moments in the rare earth and Mn sublattices of RMn 2 Ge 2 , where R is a rare earth element, feature a variety of ordering configurations. In PrMn 2 Ge 2 and TbMn 2 Ge 2 , the inter layer magnetic coupling in the Mn sublattice is, respectively, ferromagnetic and antiferromagnetic below about 350 K. At low temperatures, the rare earth sublattice also orders and reconfigures the ordering in the Mn sublattice. In this study, we investigate the variations in the magnetic properties of Pr 1− x Tb x Mn 2 Ge 2 as a function of rare earth concentration by examining the evolution of the features in the temperature dependence of the magnetization. The results of earlier neutron diffraction and Mossbauer studies on samples with x =0 and 1 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 rare earth sublattices. The results are summarized in the Pr 1− x Tb x Mn 2 Ge 2 magnetic phase diagram.

We report calorimetric and magnetization results showing that an increase in entropy is induced in a Ni–Mn–Sn ferromagnetic alloy by the application of a magnetic field, thus giving rise to an inverse magnetocaloric effect (MCE). The entropy change found for Ni–Mn–Sn is comparable to that reported for giant magnetocaloric materials but with opposite sign. This inverse MCE has the origin in a crystallographic phase change that modifies the magnetic exchange interactions through the change in the lattice parameters.

The magnetic interactions and the Fe spin structure have been studied in Fe(6 nm)/FeRh systems by magnetometry, magneto-optic Kerr effect and conversion electron Mossbauer spectroscopy. A spin-flop coupling mechanism, with the interfacial spins of the ferromagnetic phase perpendicular to the spins of the antiferromagnetic phase was experimentally proved.

As opposed to the existence of a single L2 1 parent phase in Ni 2 MnGa at room temperature, off-stoichiometric Ni 2 MnAl alloys are found in a mixed B2 (antiferromagnetic) and L2 1 (ferromagnetic) phase due to the significantly lowered B2–L2 1 ordering temperature for this compound. Despite the mixed nature of the parent phase of Ni–Mn–Al, we show that it is possible to extract information on field-induced strains occurring in the martensitic phase of Ni–Mn–Al alloys from magnetization studies.

We have studied the effect of heat treatment on the magnetic properties and on the martensitic transition of the Ni50Mn30Al20 alloy. A mixed L21+B2 state is obtained in the as-prepared sample, while no L21 order is retained in the sample quenched from high temperature. For the two heat treatments, the samples order antiferromagnetically, but there is evidence of coexisting ferromagnetic interactions. A martensitic transition occurs below the magnetic one for quenched samples. However, the martensitic transition is inhibited in the as-prepared sample.

${\text{La}}_{0.5}{\text{Pr}}_{0.5}{\text{Mn}}_{2}{\text{Si}}_{2}$ exhibits an antiferromagnetic-ferromagnetic transition caused by the crossover of the critical distance between Mn atoms on changing temperature. Applying a magnetic field in the antiferromagnetic state can cause a field-induced transformation to the ferromagnetic state at a critical field, which increases with decreasing temperature. We study here with magnetization and strain measurements the magnetic-field-induced strain associated with the field-induced transformation and magnetocaloric effects close to the transition temperature. We also examine the temperature dependence of the critical field and find from magnetization and ferromagnetic resonance measurements that short-range ferromagnetic correlation among the rare earth and Mn-sublattices occur at low temperatures. At low temperatures, this causes a decrease in the critical field for the crossover from antiferromagnetic to ferromagnetic coupling with decreasing temperature.

Applying a magnetic field to a ferromagnetic Ni$_{50}$Mn$_{34}$In$_{16}$ alloy in the martensitic state induces a structural phase transition to the austenitic state. This is accompanied by a strain which recovers on removing the magnetic field giving the system a magnetically superelastic character. A further property of this alloy is that it also shows the inverse magnetocaloric effect. The magnetic superelasticity and the inverse magnetocaloric effect in Ni-Mn-In and their association with the first order structural transition is studied by magnetization, strain, and neutron diffraction studies under magnetic field., 6 pages, 8 figures. Published in the Physical Review B

The ferromagnetic interstitial iron compound ${\mathrm{F}\mathrm{e}}_{3}\mathrm{C}$ (cementite) is expected to have Invar properties, whereby a high-moment to low-moment transition should occur when the atomic volume is reduced below a critical value. We, therefore, examine the pressure dependence of the Fe $K$-edge x-ray magnetic circular dichroism in ${\mathrm{F}\mathrm{e}}_{3}\mathrm{C}$ at ambient temperature and pressures up to 20 GPa. We find clear evidence for a high-moment to low-moment transition around 10 GPa.

The magnetocaloric effect (MCE) in paramagnetic materials has been widely used for attaining very low temperatures by applying a magnetic field isothermally and removing it adiabatically. The effect can be exploited also for room temperature refrigeration by using recently discovered giant MCE materials. In this letter, we report on an inverse situation in Ni-Mn-Sn alloys, whereby applying a magnetic field adiabatically, rather than removing it, causes the sample to cool. This has been known to occur in some intermetallic compounds, for which a moderate entropy increase can be induced when a field is applied, thus giving rise to an inverse magnetocaloric effect. However, the entropy change found for some ferromagnetic Ni-Mn-Sn alloys is just as large as that reported for giant MCE materials, but with opposite sign. The giant inverse MCE has its origin in a martensitic phase transformation that modifies the magnetic exchange interactions due to the change in the lattice parameters., Comment: 12 pages, 4 figures, to appear in Nature Materials (online published, 15 May 2005)

Fe3C incorporates only Fe as a metallic element and is an Invar material with valence electron concentration 8.67. We have studied the equation of state up to 20 GPa of Fe3C particles sd ,40 nmd below and above the Curie temperature (room temperature and 550 K, respectively) to search for a softening associated with a magnetovolume instabilities characteristic of Invar-type material. The isothermal bulk modulus of Fe3C particles at room temperature was found to be about 13% smaller than that of the value at 550 K. This difference is comparable with the relative difference in the bulk modulus of Fe65Ni35 Invar in a similar temperature range around the Curie temperature.

The structural and magnetic properties of stoichiometric Ni2MnAl are studied to clarify the conditions for ferromagnetic and antiferromagnetic ordering claimed to occur in this compound. X-ray and magnetization measurements show that although a single phase B2 structure can be stabilized at room temperature, a single L21 phase is not readily stabilized, but rather a mixed L21+B2 state occurs. The mixed state incorporates ferromagnetic and antiferromagnetic parts for which close-lying Curie and a Neel temperatures can be identified from magnetization measurements.

Measurements of magnetic hysteresis loops in Cu-Al-Mn alloys of different Mn content at low temperatures are presented. The loops are smooth and continuous above a certain temperature, but exhibit a magnetization discontinuity below that temperature. Scaling analysis suggest that this system displays a disorder induced phase transition line. Measurements allow to determine the critical exponents $\beta=0.03\pm 0.01$ and $\beta \delta = 0.4 \pm 0.1$ in agreement with those reported recently [Berger et al., Phys. Rev. Lett. {\bf 85}, 4176 (2000)], Comment: 4 pages, 5 figures

Measurements of magnetic hysteresis loops performed at low temperatures on Cu–Al–Mn alloys with different Mn-content are presented. The loops are smooth and continuous above a certain temperature, while they exhibit a magnetization discontinuity below this temperature. Scaling analysis suggests that this system displays a disorder-induced phase transition line and allows determining the critical exponents (β=0.03±0.01 and βδ=13±3). Results indicate that by changing temperature, it is possible to tune the disorder responsible for the transition.

Thermal variation and dependence on Cu-layer thickness t Cu ( t Cu =7.6–25.7 A) of magnetoresistance (MR) and the magnetization (M) of [Co(10.2 A)/Cu( t Cu )] 25 magnetic multilayers (MMLs) have been measured between 4.2 and 300 K. So as long as the magnetization of adjacent Co layers are aligned antiparallel, the MR increases with decreasing temperature. This temperature dependence becomes weak as the antiparallel coupling weakens, and it is almost temperature-independent for samples with t Cu where the magnetization is aligned parallel. The temperature dependence of MR for t Cu =11.4 A, for which the coupling crosses over from antiparallel to parallel, is complex.

We have investigated the magnetic properties of La x R 1− x Mn 2 Si 2 for various rare-earth elements 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 x =0 and 1 from neutron diffraction studies, the low field magnetization can give information on the magnetic structure of the compounds at intermediate concentrations. The volume dependence of the transition temperatures pertaining to the Mn sublattice is clearly found to be almost independent of the type of R.

We study the mechanism of magnetic-field-induced reverse martensitic transformations by considering the field-induced temperature-shifts in the thermal hysteresis loop of the magnetization and critical fields determined from magnetization isotherms. We consider first the temperature-shifts in a symmetric thermal hysteresis loop and extend the discussion to the case of the Heusler-based Ni50Mn34In16 magnetically superelastic alloy having a nonsymmetric thermal hysteresis loop. We obtain two different temperature-behaviors for the critical field depending on whether the initial measurement temperature lies on the forward or on the reverse transformation path of the thermal hysteresis.

The magnetic and magnetocaloric properties of La0.8Sm0.2Mn2Si2 and La0.775Gd0.225Mn2Si2 compounds have been studied by temperature- and magnetic field-dependent magnetic measurements. Both compounds crystallize in the ThCr2Si2-type structure with the space group I4/mmm. Both compounds exhibit reentrant magnetic phase transitions and field-induced transitions from antiferromagnetic to ferromagnetic or ferrimagnetic state. The isothermal magnetic entropy change is estimated by using the Maxwell relation and Landau theory. Both compounds show inverse and conventional magnetocaloric effects around transition temperatures. Application of Landau theory on magnetic transitions shows good agreement with the result obtained by Maxwell theory.

At certain compositions Ni-Mn-$X$ Heusler alloys ($X$: group IIIA-VA elements) undergo martensitic transformations, and many of them exhibit inverse magnetocaloric effects. In alloys where $X$ is Sn, the isothermal entropy change is largest among the Heusler alloys, particularly in Ni$_{50}$Mn$_{37}$Sn$_{13}$ where it reaches a value of 20 Jkg$^{-1}$K$^{-1}$ for a field of 5T. We substitute Ni with Fe and Co in this alloy, each in amounts of 1 at% and 3 at% to perturb the electronic concentration and examine the resulting changes in the magnetocaloric properties. Increasing both Fe and Co concentrations causes the martensitic transition temperature to decrease, whereby the substitution by Co at both compositions or substituting 1 at% Fe leads to a decrease in the magnetocaloric effect. On the other hand, the magnetocaloric effect in the alloy with 3 at% Fe leads to an increase in the value of the entropy change to about 30 Jkg$^{-1}$K$^{-1}$ at 5T., Comment: 5 pages, 7 figures. Accepted for publication in the Journal of Applied Physics

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.