Magnetic Phase

Transitions in Intercalated

Dichalcogenide

Nanostructures

CORBYN MELLINGER

UNIVERSITY OF NORTHERN IOWA

Intercalated Dichalcogenide

Nanostructures

Layered material made up of TaS2 with

magnetic Mn ions between layers

Concentration of Mn determines

magnetic properties

Our sample: Mn0.235TaS2

(Layered structure of MnxTaS2))

(SEM image of MnxTaS2 nanotubes)

Magnetism Background

Atoms possess orbital

and spin angular

momentum

These spins contribute

to “magnetic

moments”

Magnetic phase of

material depends on

short-range and long-

range order of

individual momentsA: Paramagnetic

B: Ferromagnetic

Objectives

Characterize magnetic phase transitions in Mn0.235TaS2

nanostructures

Previous research characterize transitions for 15%, 20%, and 23%

intercalation

Build phase diagram for general MnxTaS2 as a function of

x

AC Susceptibility vs. Temperature

Data down to T ~ 75 K behaves

in accordance with Curie-Weiss

Law

χ =C

T−θ

Indicative of paramagnetic

to ferromagnetic transition

Peak at T ~ 40 K indicates

second magnetic phase

transition

Ferromagnetic to cluster-

glass

Upper Transition

Behavior of transition governed by critical exponents βand γ

χ0 T ∝T−Tc

Tc

−γ(T > Tc)

Ms(T) ∝T−Tc

Tc

β(T < Tc)

Given appropriate β and γ, plot of M 1 β vs. χ0−1 1 γ will

produce straight lines of given isotherms

Arrott-Noakes Analysis

Arrott-Noakes Analysis

Exponents selected using iterative

code in MATLAB

Many sets of values tried; set

returning straightest lines reported

back by program

Tc given as isotherm which

intersects origin

Kouvel-Fisher Analysis

Related to equations of

state

χ0−1 ∙

dχ0−1

dT

−1

=T−Tc

γ

Ms ∙dMs

dT

−1=

T−Tc

β

Does not require

exponents to be known

before analysis

Lower Transition

Spin Glass

Individual spins “locked” in

place

Small time dependence for

alignment of moments with

external field

Cluster Glass

Groups of spins “locked”

Similarly small time

dependence on external field

Vogel-Fulcher Plot

AC susceptibility

measurements

performed at

frequency 𝑓

1

f= τ = τ0e

E0

kB T−Tg

Phase Diagram

Adjusted phase

diagram based on

new x = 0.235 data

More points desired

near multicritical

point (x~0.225) and

for higher x

Conclusions & Analysis

Upper Transition

PM→FM transition has critical exponent values β =0.86 and γ =1.22 and takes place at Tc = 74.4 K

γ is in line with 3D Heisenberg models, but β is larger than model predicts

Reentrant magnetic state likely contains mixture of FM and CG states, leading to suppressed FM behavior

Lower Transition

FM→CG transition occurs at

T = 39.6 K

τ0 and E0

kBvalues are within

reasonable bounds to

accept the conclusion that

the lowest magnetic state is

that of cluster glass

Acknowledgements

National Science Foundation Award No. DMR-1206530

Department of Physics, University of Northern Iowa

Dr. Paul Shand