Abstract
We report the structural and magnetic behavior of single phase inverse Heusler alloys Cr2Co(1−x)CrxAl (x = 0, 0.2, and 0.4) by using x-ray diffraction (XRD), Raman spectroscopy, isothermal magnetization, and magnetic susceptibility measurements. Interestingly, the Rietveld refinement of XRD data with space group I4¯m2 reveal a tetragonal distortion with a c/a ratio around 1.38 in these inverse Heusler structures. The bulk compositions have been confirmed by energy dispersive x-ray spectroscopy measurements. The active Raman mode F2g is observed at 320 cm−1, which confirms the X-type Heusler structure, as the A2 and B2 type structures are known to be not Raman active. The area of F2g mode decreases with an increase in the Cr concentration, which indicates that the origin of this mode is due to Co vibrations. The isothermal magnetization data confirm the magnetic moment to be close to zero (≤0.02 μB/f.u.) at ≈70 kOe and the negligible coercive field suggests the fully compensated ferrimagnetic nature of these samples. The susceptibility behavior indicates irreversibility between zero-field and field-cooled curves and complex magnetic interactions at low temperatures.
Highlights
Many Co-based Heusler alloys (HAs) have been studied extensively due to their structural stability and half-metallic ferromagnetic (HMF) nature, and they have an advantage of possessing high Curie temperatures (TC)2,3 and exhibit the spin gapless semiconducting properties
In the X2YZ type full-Heusler alloys, the unit cell consists of four interpenetrating fcc sublattices with the positions A (0, 0, 0), B (0.25, 0.25, 0.25), C (0.5, 0.5, 0.5), and D (0.75, 0.75, 0.75)
The lattice constant values obtained from the x-ray diffraction (XRD) patterns and the tetragonality ratios (c/a) are summarized in Table I for all three samples, which agree with the reported values for Cr2CoGa in Ref. 18 We found an increment in the lattice parameters with the substitution of Cr at the site of Co, which is expected, as the atomic radius of Cr (128 pm) is larger than that of Co (125 pm)
Summary
The full Heusler alloys are X2YZ type ternary intermetallic compounds having X and Y as transition metals and Z as a main group element or an sp-element.1 In recent years, many Co-based Heusler alloys (HAs) have been studied extensively due to their structural stability and half-metallic ferromagnetic (HMF) nature, and they have an advantage of possessing high Curie temperatures (TC)2,3 and exhibit the spin gapless semiconducting properties.4,5 In the family of CoCr based full-Heusler alloys, Co2CrAl has attracted huge attention due to its true half-metallic ferromagnetic (HMF) nature with 3 μB/f.u. magnetic moment as per the band structure calculations and the Slater–Pauling rule.6,7 It is interesting to note here that Luo et al studied the effect of Cr substitution on the Co site and showed a transition from the HMF state to the HM fully compensated ferrimagnetic (FCF) state.8 the appreciable value of spin polarization of about 68% was reported for Cr2CoAl.9 This is found to be the most important material because by changing the Cr concentration, we can tune the magnetic moment from 3 μB/f.u. to zero without destroying the half-metallicity.8 These compounds show the largest value of spin density among all known ferromagnetic half-metals so far.
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