Magnetic behavior of CeFe2: Effects of Ru, Rh, and Pd substitutions

First order magneto-structural phase transition and associated multi-functional properties in magnetic solids

We show that the first order magneto-structural phase transitions observed in various classes of magnetic solids are often accompanied by useful multi-functional properties, namely giant magneto-resistance, magneto-caloric effect and magneto-striction. We highlight various characteristic features associated with a disorder influenced first order phase transition namely supercooling, superheating, phase-coexistence and metastability, in several magnetic materials and discuss how a proper understanding of the transition process can help in fine tuning of the accompanied functional properties. Magneto-elastic coupling is a key element in this first order phase transition, and methods need to be explored for maximizing the contributions from both the lattice and the magnetic degree of freedom while simultaneously minimizing the thermomagnetic hysteresis loss. An analogy is also drawn with the first order phase transition observed in dielectric materials and vortex matter of type-II superconductors.

Disorder influenced magnetic phase transition in the Ce(Fe 0.9 Ru 0.1)2 alloy

We have studied a 10% Ru-doped CeFe(2) alloy, Ce(Fe(0.9)Ru(0.1))(2), through magnetization, magnetotransport, and heat capacity measurements. This study shows that, while this alloy is antiferromagnetic at low temperatures and paramagnetic at high temperatures, there exists evidence of ferromagnetic ordering in the intermediate temperature regime. We show here that with 10% Ru doping the first order magnetic transition observed in the Ce(Fe(1 - x)Ru(x))(2) alloys with x < 0.08 is reduced to a quasi-continuous phase transition. The characteristic thermomagnetic history effects associated with the ferromagnetic-antiferromagnetic phase transition in the Ce(Fe(1 - x)Ru(x))(2) alloys with x < 0.08 are not observed in the Ce(Fe(0.9)Ru(0.1))(2) alloy. This alloy continues to exhibit the large magnetoresistance and large magnetocaloric effect associated with this first order magnetic transition in the alloys with smaller Ru concentration, but it does not show any energy loss due to thermomagnetic hysteresis. The present work thus shows how the introduction of quenched disorder due to alloying effects may be used to tune the first order magnetic transition in a material for more efficient functional use.

Stabilization of antiferromagnetism in CeFe(2) alloys: the effects of chemical and hydrostatic pressure

Effects of Al, Mn and Sb dopings in CeFe(2) and the effect of applied pressure have been investigated. Al doping gives rise to the FM-AFM transition and a reduction in the magnetic moment and T(C) values, clearly indicating the growth of the AFM component. Mn and Sb dopings only cause a reduction in the T(C) value. It is found that, in general, external pressure enhances the antiferromagnetism in both the pure and the doped alloys. Enhancement of the Ce 4f-Fe 3d hybridization as a result of doping and with the external pressure may be the reason for the stabilization of antiferromagnetism in these alloys.

First order magnetic transition in doped CeFe2 alloys: phase coexistence and metastability

First order ferromagnetic (FM) to antiferromagnetic (AFM) phase transition in doped CeFe2 alloys is studied with the micro-Hall probe technique. Clear visual evidence of magnetic phase coexistence on micrometer scales and the evolution of this phase coexistence as a function of temperature, magnetic field, and time across the first order FM-AFM transition is presented. Such phase coexistence and metastability arise as a natural consequence of an intrinsic disorder-influenced first order transition. The generality of these phenomena involving other classes of materials is discussed.