Complex exchange mechanism driven ferromagnetism in half-metallic Heusler Co 2 TiGe : Evidence from critical behavior

Heusler alloys have drawn considerable interest, due to their tunable properties, for technological applications. The literature review reveals that the critical exponents and magnetocaloric effect (MCE) of Co2TiAl0.75Si0.25 quaternary Heusler alloy need to be established. Hence, Co2TiAl0.75Si0.25 alloy is prepared by the arc melting method. Critical exponents of the alloy are obtained by analyzing magnetic isotherms with various techniques, such as Arrot plots, Kouvel–Fisher plots, critical isotherm analysis, and magnetocaloric analysis near the transition temperature. The paramagnetic to ferromagnetic transition temperature is found to be ≈235 ±2.5 K. The nature of the Arrot plots and the universal curve of the MCE confirm this as a second‐order phase transition. Despite the moderate magnetocaloric values, the large working temperature (≈75 K at 3 T) makes this alloy a potential candidate for a multistage magnetic refrigeration application. The critical exponents obtained from different techniques fall in between the theoretical prediction from the mean field theory, which indicates long‐range ferromagnetic exchange interaction, and the 3D Heisenberg model, implying short‐range interaction. The range of interaction (σ = 1.727) also confirms this. This complex magnetic interaction may arise from the competition between localized and itinerant electron present in the system.

“…3D Heisenberg model [15] 0.365 1.386 4.80 3D Ising model [15] 0.325 1.241 4.82 Co 2 TiGe [7] 0.495 1.324 3.67 Co 2 TiSn [10] 0.537 1.255 3.33…”

Section: Resultsmentioning

confidence: 99%

Section: Isothermal Magnetizationmentioning

confidence: 99%

Section: Isothermal Magnetizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…Variation of spontaneous magnetization and inverse susceptibility with temperature. The solid lines represent the fitting with Equation(6)and(7).…”

mentioning

confidence: 99%

See 3 more Smart Citations

Correlation between Critical Behavior and Magnetocaloric Effect near Paramagnetic to Ferromagnetic Phase Transition of Co₂TiAl_0.75Si_0.25 Heusler Alloy

Datta

Guha

Panda

et al. 2020

Anomalous Hall Effect and Magnetoresistance in Sputter‐Deposited Magnetic Weyl Semimetal Co₂TiGe Thin Films

Dyck

Becker

Koo

et al. 2020

Herein, sputter‐deposited ferromagnetic Weyl semimetal (WSM) and full‐Heusler compound Co2TiGe is investigated. Crystal quality is analyzed using X‐ray diffraction and reflectivity. In addition, temperature‐dependent transport and magnetization measurements are carried out. The sample shows indications on the formation of L21 crystal structure. Magnetization measurements show a saturation magnetization of 1.98 μB (f.u.)−1 and 1.45 μB (f.u.)−1 at 50 and 300 K, respectively. This is in close agreement to the calculated value of 2 μB (f.u.)−1 at 0 K using the Slater–Pauling rule. The obtained Curie temperature is 378.5 K, which is close to prior results for bulk samples. The residual resistivity of 142.7 μΩ cm is mainly dominated by disorder scattering. At temperatures above 60 K, the Coulomb interaction dominates the resistance. The residual resistance ratio is around 1.49. Hall measurements show positive ordinary Hall and anomalous Hall constants and a positive dependence on temperature. Skew scattering and side jumps or intrinsic mechanisms contribute in similar amounts to the anomalous Hall resistivity, which indicates a higher than usual intrinsic contribution, which is expected for WSMs. The expected relation between the longitudinal and the anomalous Hall conductivity of is not met.

The Emergence of an Itinerant Ferromagnetic State in Co‐Doped YNi₅: A Critical Behavior Study of the Phase Transition

Karmakar

Giri

Majumdar

2020

YNi5 is an enhanced Pauli paramagnetic material, and this work is devoted to the effect of Co doping at the Ni site of YNi5. It is found that at 10% Co doping, the sample turns ferromagnetic, with a weak itinerant character. The critical behaviours of the 10% Co‐doped sample (i.e., YNi4.5CO0.5) in its polycrystalline form are examined through bulk magnetization measurements. The second‐order phase transition from the paramagnetic to the ferromagnetic state is confirmed by the positive slope of the Arrott plots. To obtain the most reliable values of the critical exponents, an extensive analysis of the magnetization data is performed, which includes a modified Arrott plot, Kouvel–Fisher plot, and critical isotherm analysis. The best values of the exponent obtained are β = 0.179 (±0.002), γ = 1.429 (±0.002), and TC = 9.1 K. These values are close to a 2D Ising model along with the long‐range exchange decaying as J(r) ≈ r−(3.6). It is found that this extended exchange is a typical characteristic of many itinerant ferromagnets, whereas the 2D nature is likely to be connected with the layered crystal structure.