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Anisotropic Kondo Effect in a 3d transition metal compoundAhmad Us Saleheen1 , Tapas Samanta1, Daniel L. Lepkowski1, Alok Shankar1, Joseph Prestigiacomo1, Igor Dubenko2, Abdiel Quetz2, Iain W. H. Oswald3, Gregory T.

McCandless3, Julia Y. Chan3, Philip W. Adams1, David P. Young1, Naushad Ali2, and Shane Stadler1

1Department of Physics & Astronomy, Louisiana State University, Baton Rouge, LA 70803 2Department of Physics, Southern Illinois University, Carbondale, IL 62901 3Department of Chemistry, The University of Texas at Dallas, Richardson, TX 75080

Abstract

Background

Results Results Results

Conclusion

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We report an anisotropic Kondo effect in purely 3d

transition metal ferromagnetic (FM) system (i.e., not rare-

earth-based). The isostructural alloying of two compounds

having collinear magnetic structure has resulted in a FM

Kondo lattice system, Mn1-xFexCoGe in the proximity of a

noncollinear FM state with x = 0.2. Resistivity, magnetic

susceptibility and heat capacity studies on single crystal

sample indicate that the Kondo effect is anisotropic. An

increase in resistivity along two principal direction at low-

temperature has been observed with the decrease in T,

which follows a lnT behavior below the Kondo minimum

(TK) due to Kondo scattering. However, TK along i∥c is

about two times higher than that of along i⊥c. Directional

dependence of magnetization also mimics the similar

behavior by showing pronounced Kondo screening along

c-axis. Large saturation magnetization at low-temperature

indicates that it is a underscreened Kondo Effect.

Underscreening of moments may lead to the coexistence

of FM and Kondo behavior.

For x=0.2 composition Kadowaki-Woods ratio of

𝐴 𝛾2~43 μΏ.cm.mol2.K2.J-2 was observed. This

indicates strong electron correlation in

Mn1-xFexCoGe system. According to Rhodes-

Wohlfarth model large PC/MS value indicates

itinerant behavior (Rhodes and Wohlfarth,

Proc.Roy.Soc.London 273,247, 1963). We can see

a transition to more itinerant behavior with the

increase in Fe content. At x=0.2 composition, a

transition from localized to itinerant behavior is

expected (Samanta et

al.,Appl.Phys.Lett.103,042408, 2013).

Resistivity:

We observed an increase in ρ at low temperature

with the decrease in T. It follows a lnT behavior

below the Kondo minimum due to Kondo

scattering (inset).

TK along i∥c is around two times greater than that of

along i⊥c. This behavior may indicate a more

pronounced Kondo behavior along c axis.

Magnetization:

Structure:

Single crystals of Mn0.8Fe0.2CoGe were grown using Sn flux.

XRD data indicates a Ni2In type hexagonal structure. Lattice

parameters are: a=4.06 A0 and c= 5.20A0 .

Strong anisotropy in both directions is evident from

magnetization measurements.

Heat Capacity:

After fitting the low temperature data a large value of

γ= 25.3 mJ/mol K2 was found, indicating the formation of

heavy quantum particle with effective mass enhancement

of approximately 30 times that of free electrons.

𝐷0 𝐸𝐹 = 15.1 states/eV/f.u. was estimated from the γ

value and which is three times larger than that of the

parent compound MnCoGe (Samanta et al., 2013).

We observed two different Kondo minima in two different axial

directions. Until now, the reason for this behavior is not entirely

clear to us. We can also see high MS in both directions in spite

of Kondo type increase in ρ below TK . From low temperature

magnetization data it was revealed that it is an S=1 system.

Underscreening of moments may lead to the coexistence of FM

and Kondo behavior.

Acknowledgement

This work is supported by U.S. Dept. of Energy (Grant Nos.

DE-FG02-06ER46291,DE-FG02-13ER46946 and DE-FG02-

07ER46420). Ahmad Us Saleheen acknowledges support from

LA-SiGMA .