The strong dependence of the field-induced on the body-centered tetragonal ThCr2Si2-type and the critical behaviour of magnetic phase transition in NdMn2-xCuxSi2based compounds guide us to study the substitution Mn (atomic radius = 1.35 Å) by Cu (atomic radius = 1.28 Å) in layered NdMn1.4Cu0.6Si2compound. Room temperature x-ray diffraction study indicates clearly that most of the reflections can be identified with ThCr2Si2-type structure with space group I4/mmm. It found lattice parameters a slightly increases and lattice parameter c decrease compare to NdMn2Si2as indicated the decreasing of volume structure. The Neel temperature TNis found at 340 K while Curie temperature TCfound at 75 K respectively. The increasing concentration of Cu in replacement of Mn changes the magnetic phase transition from first order type for NdMn2Si2to second order type for layered NdMn1.4Cu0.6Si2compound as been determined by particular the S-shaped nature of the Arrott plot near TC. Our results indicate that the magnetic-field-induced magnetic phase transition plays a critical role on producing large magnetocaloric effect in these systems especially on second order type as the key for further investigation. The critical behaviour analysis in the vicinity of TCdemonstrates that the magnetism of the layered NdMn1.4Cu0.6Si2compound is governed by long range interactions.

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1.69 Compounds. -All title compounds with x ≤ 0.6 crystallize in the Nd 3 (Fe,Ti) 29 -type structure. Substitution of Ho for Nd leads to a contraction of the unit cell volume. Magnetic measurements indicate that the Curie temperature of the title compounds is almost independent of the Ho content, whereas the saturation moments decrease monotonically with increasing x. For all compounds investigated a spin reorientation from easy plane to easy cone occurs when the temperature decreases from room temperature to 5 K. A tentative spin phase diagram is given. -(WANG*, W. Q.; WANG, J. L.; YAN, Y.; DU, X. B.; WANG, X. F.; JIN, H. M.; J.