Magnetic and Magnetocaloric Properties of the New Rare-Earth-Transition-Metal Intermetallic Compound Gd3Co29Ge4B10

The compounds Gd3-xYxCo29Ge4B10 (x = 0, 0.5, 1.0, 1.5, and 3.0), Gd3Co29Al4B10, and Gd3Co29Al4B10 were synthesized by arc melting, and their magnetic properties investigated as a function of temperature and applied magnetic field. X-ray measurements showed primarily single-phase samples with the tetragonal crystal structure P4/nmm. It was found that Gd3Co29Ge4B10 orders ferromagnetically at TC  = 212 K and shows a compensation point at 128 K, indicating a ferrimagnetic ordering of the Co and Gd moments. An entropy change of −ΔS = 0.5 J/kgK was observed in a 5-T field at TC for this sample, while a change in sign for this quantity was observed both at the maximum value of magnetization (around 200 K) and then again at the compensation point. Substitution of Y for Gd in Gd3Co29Ge4B10 does not affect the Curie temperature, but shifts the compensation point to lower temperatures. This indicates that a decrease in Gd concentration does not affect the d-d exchange interaction, but has a pronounced effect on the f-d exchange interaction

Large Magnetocaloric Effects over a Wide Temperature Range in MnCo\u3csub\u3e1-x\u3c/sub\u3eZn\u3csub\u3ex\u3c/sub\u3eGe

The magnetic and structural transitions can be controlled to coincide by partial substitution of Zn for Co in MnCo1-xZnxGe, leading to a large magnetocaloric effects over a wide temperature range. The magnetostructural transition from paramagnetic to ferromagnetic state results in magnetic entropy changes (Delta SM) of 26 J/kg K at 327K for Delta H = 5 T in the case of x = 0.045. Interestingly, a structurally driven first-order phase transition between two high magnetization states as observed for x = 0.05 and 0.06 also lead to large values of -Delta SM = 31.4 and 20.6 J/kg K for Delta H = 5 T at 281 and 209 K, respectively. The observed large magnetocaloric effects with tunable phase transition temperatures make these materials promising for near room-temperature magnetic cooling applications

Large magnetocaloric effects over a wide temperature range in MnCo 1-xZnxGe

The magnetic and structural transitions can be controlled to coincide by partial substitution of Zn for Co in MnCo1-xZnxGe, leading to a large magnetocaloric effects over a wide temperature range. The magnetostructural transition from paramagnetic to ferromagnetic state results in magnetic entropy changes (-ΔSM) of 26 J/kg K at 327 K for ΔH 5 T in the case of x 0.045. Interestingly, a structurally driven first-order phase transition between two high magnetization states as observed for x 0.05 and 0.06 also lead to large values of -ΔSM 31.4 and 20.6 J/kg K for ΔH 5 T at 281 and 209 K, respectively. The observed large magnetocaloric effects with tunable phase transition temperatures make these materials promising for near room-temperature magnetic cooling applications. © 2013 American Institute of Physics

Phase Transitions and Magnetocaloric Properties in MnCo1- xZrxGe Compounds

The structural, magnetic, and magnetocaloric properties of MnCo1-xZrxGe (0.01≤x≤0.04) have been studied through X-ray diffraction, differential scanning calorimetry, and magnetization measurements. Results indicate that the partial substitution of Zr for Co in MnCo1-xZrxGe decreases the martensitic transition temperature (TM). For x = 0.02, TM was found to coincide with the ferromagnetic transition temperature (TC) resulting in a first-order magnetostructural transition (MST). A further increase in zirconium concentration (x = 0.04) showed a single transition at TC. The MST from the paramagnetic to ferromagnetic state results in magnetic entropy changes (-ΔSM) of 7.2 J/kgK for ΔH = 5 T at 274 K for x = 0.02. The corresponding value of the relative cooling power (RCP) was found to be 266 J/kg for ΔH = 5 T. The observed large value of MCE and RCP makes this system a promising material for magnetic cooling applications

Magnetostructural Phase Transitions and Magnetocaloric Effects in MnNiGe1-xAlx

The thermomagnetic and magnetocaloric properties of the MnNiGe1−xAlx system have been investigated by magnetization and differential scanning calorimetry (DSC) measurements. The presence of first-order magnetostructural transitions (MSTs) from hexagonal ferromagnetic to orthorhombic antiferromagnetic phases has been detected for x = 0.085 and 0.09 at 193 K and 186 K, respectively. The values of latent heat (L = 6.6 J/g) and corresponding total entropy changes (ΔST = 35 J/kg K) have been evaluated for the MST (x = 0.09) from DSC measurements. The magnetic entropy change for x = 0.09 (ΔSM = 17.6 J/kg K for 5 T) was found to be comparable with well-known giant magnetocaloric materials, such as Gd5Si2Ge2, MnFeP0.45As0.55, and Ni50Mn37Sn13

Large inverse magnetocaloric effects and giant magnetoresistance in Ni-Mn-Cr-Sn heusler alloys

The magnetostructural transitions, magnetocaloric effects, and magnetoresistance properties of Ni45Mn43CrSn11 Heusler alloys were investigated using X-ray diffraction (XRD), field-dependent magnetization, and electrical resistivity measurements. A large inverse and direct magnetocaloric effect has been observed in Ni45Mn43CrSn11 across the martensitic and Curie transition temperature, respectively. The values of the latent heat (L = 15.5 J/g) and corresponding magnetic (∆SM) and total (∆ST) entropy changes (∆SM = 35 J/kg·K for ∆H = 5T and ∆ST = 39.7 J/kg·K) have been evaluated using magnetic and differential scanning calorimetry (DSC) measurements, respectively. A substantial jump in resistivity was observed across the martensitic transformation. A large negative magnetoresistance (~67%) was obtained at the magnetostructural transition for a field change of 5 T. The roles of the magnetic and structural changes on the transition temperatures and the potential application of Ni45Mn43CrSn11 Heusler alloys for refrigerator technology are discussed

Mn\u3csub\u3e1-x\u3c/sub\u3eFe\u3csub\u3ex\u3c/sub\u3eCoGe: A Strongly Correlated Metal in the Proximity of a Noncollinear Ferromagnetic State

An unusually large Kadowaki-Woods ratio of A/gamma2 similar to 43 mu Omega.cm.mol2.K2.J-2 has been observed for intermetallic Mn1-xFexCoGe compounds in the proximity of x = 0.2 where the magnetic state of itinerant electrons system changes. The ratio is approximately four times larger than observed for heavy fermion systems. The manifestation of the strong electron correlations can be realized from the anisotropic origin of the effect through the substantial reduction of interlayer transport of heavy quasiparticles with comparable mean-free path and interlayer spacing in the proximity of a noncollinear ferromagnetic state associated with a large density of states at the Fermi level

Magnetic, structural and magnetocaloric properties of Ni-Si and Ni-Al thermoseeds for self-controlled hyperthermia

Self-controlled hyperthermia is a non-invasive technique used to kill or destroy cancer cells while preserving normal surrounding tissues. We have explored bulk magnetic Ni-Si and Ni-Al alloys as a potential thermoseeds. The structural, magnetic and magnetocaloric properties of the samples were investigated, including saturation magnetisation, Curie temperature (TC), and magnetic and thermal hysteresis, using room temperature X-ray diffraction and magnetometry. The annealing time, temperature and the effects of homogenising the thermoseeds were studied to determine the functional hyperthermia applications. The bulk Ni-Si and Ni-Al binary alloys have Curie temperatures in the desired range, 316 K–319 K (43 °C–46 °C), which is suitable for magnetic hyperthermia applications. We have found that TC strictly follows a linear trend with doping concentration over a wide range of temperature. The magnetic ordering temperature and the magnetic properties can be controlled through substitution in these binary alloys

Thermosensitive Ni-based magnetic particles for self-controlled hyperthermia applications

A number of ferromagnetic alloys in the bulk-form “thermoseeds” have been investigated for localized self-controlled hyperthermia treatment of cancer by substituting V, Mo, Cu, and Ga for Ni. The samples were prepared by arc-melting technique and annealed at 1223 K (950 °C) for 12 h in sealed quartz tubes. The structural, magnetic, and magnetocaloric properties of the samples were studied, using room temperature X-ray diffraction and a Superconducting Quantum Interference Device (SQUID) magnetometer. The magnetocaloric parameters (magnetic entropy changes, refrigeration capacity (RC), and hysteretic effects) have been calculated. It has been shown that recrystallization, i.e., annealing time and temperature, is crucial for controlling the heating characteristics of the seeds. A linear decrease in Curie temperature (TC) from 380 K (107 °C) to 200 K (−73 °C) was observed with increasing substitution of Ni by V, Mo, Cu, and Ga, while the magnetization value remained nearly constant for all substitutions. The optimal composition of these Ni-based alloys has been determined in order to allow self-controlling hyperthermia, implying a Curie temperature near the therapeutic level, 315–318 K (41–45 °C). The results showed that an extraordinary self-regulating heating effect has been achieved in Ni-based magnetic materials, which may create new vistas for hyperthermia cancer treatment