Magnetic field – temperature phase diagram

of multiferroic (NH4)2FeCl5∙H2O

A. J. Clune, K. D. Hughey, A. L. Blockmon, J. L. Musfeldt (UT); J. Nam, M. Lee, J. H. Lee (UNIST); W.

Tian, R. S. Fishman (ORNL); J. Fernandez-Baca (ORNL & UT); J. Singleton, M. Lee, V Zapf (LANL)

Objectives:

• explore molecule-based multiferroic (NH4)2FeCl5∙H2O in high magnetic fields

• reveal complex B-T phase diagram

• enable new types of property investigations

image of a single crystal

Multifunctional material vs. multiferroics?

Schmidt (1996); Spaldin + Fiebig, Science (2005)

E → P

σ → εH → M

Multifunctional: must combine >1 interesting functionalities

What are they?

ferroelectricity

ferromagnetism ferrotoroidicity

ferroelasticity

Extending this definition to include

non-primary order parameters…

ferrimagnetism antiferromagnetism

Appear in different forms…

single phase

composites

heterostructues

Cross-coupling gives rise to rich phase diagrams!

nanoparticles

Multiferroics: must have >1 primary ferroic order parameter

why molecule-based multiferroics?• molecule-based multiferroics

• low energy scales• flexible architecture

• chemical substitution• experimentally accessible fields!

• field-induced transitions to fully-saturated state under-explored

• how to fix this? • develop phase diagrams!• reveal properties

A. Clune, et al., PRB (2017)A. Narayan, et al., Nat. Mater. (2019)

[(CH3)2NH2]Mn(HCOO)3

Erythrosiderite (NH4)2FeCl5∙H2O

• space group: Pnma

• Fe+3 = 5/2

• TO/D = 79 K

• TN = 7.25 K

• TFE = 6.9 K

• multiferroic!

• mechanism is curious

(a) (d)(b)

(c)

6.4 6.8 7.20.0

0.5

1.0

1.5

2.0

2.5

J3

J4

J2

J5

-J (

K)

Distance between FeFe (Å)

J1(H

2O)

image of a single crystal

oh, the places you will go!

exotic properties emerge when phases compete!

Erythrosiderite (NH4)2FeCl5∙H2O

Ackermann, et al, New Journal of Physics (2013)

but what about the high field behavior?

Competition between exchange pathways

J1 = -2.51 KJ2 = -1.55 K

J4 = -1.25 K J5 = -0.71 K

J3 = -0.27 K

(a) (d)(b)

(c)

6.4 6.8 7.20.0

0.5

1.0

1.5

2.0

2.5

J3

J4

J2

J5

-J (

K)

Distance between FeFe (Å)

J1(H

2O)

Frustration!

Hydro

gen

tate

d, B

|| c

0 10 20 300.0

0.5

1.0

BSat

= 30.3 T

M/M

Sat

Magnetic Field (T)

0.60 K(a)

15 20 25 30

(f)

M

/B

Magnetic Field (T)

0.60 K

1.59 K

2.16 K2.54 K

3.09 K

3.62 K4.12 K

1 2 3 4 5 6

(e)

M

/B

Magnetic Field (T)

0.60 K1.59 K3.09 K4.12 K5.50 K

6.75 K6.25 K

0 10 20 300.0

0.5

1.0 (d)

BSat

= 30.3 T

M/M

Sat

Magnetic Field (T)

0.62 K

0 10 20 300.0

0.5

1.0 (c)

M/M

Sat

Magnetic Field (T)

0.66 K

BSat

= 31.1 T

0 10 20 300.0

0.5

1.0 (b)

BSat

= 30.1 T

M/M

Sat

Magnetic Field (T)

0.62 K

3.0 4.5 6.0

M

/B

Magnetic Field (T)

3.5 4.0 4.5

M

/B

Magnetic Field (T)

3.0 4.5

M

/B

Magnetic Field (T)

3.5 4.0 4.5

M

/B

Magnetic Field (T)

Mag

net

ic f

ield

|| a

Hydrogentated Deuterated

Mag

net

ic f

ield

|| c

Driving to the fully saturated state

• two sets of transitions

• Blow field < 6 T

• BSat ≈ 30 T

• shape consistent with

3D materials

Derivatives to reveal magnetic transitions

Hydro

gen

tate

d, B

|| c

0 10 20 300.0

0.5

1.0

BSat

= 30.3 T

M/M

Sat

Magnetic Field (T)

0.60 K(a)

15 20 25 30

(f)

M

/B

Magnetic Field (T)

0.60 K

1.59 K

2.16 K2.54 K

3.09 K

3.62 K4.12 K

1 2 3 4 5 6

(e)

M

/B

Magnetic Field (T)

0.60 K1.59 K3.09 K4.12 K5.50 K

6.75 K6.25 K

0 10 20 300.0

0.5

1.0 (d)

BSat

= 30.3 T

M/M

Sat

Magnetic Field (T)

0.62 K

0 10 20 300.0

0.5

1.0 (c)

M/M

Sat

Magnetic Field (T)

0.66 K

BSat

= 31.1 T

0 10 20 300.0

0.5

1.0 (b)

BSat

= 30.1 T

M/M

Sat

Magnetic Field (T)

0.62 K

3.0 4.5 6.0

M

/B

Magnetic Field (T)

3.5 4.0 4.5

M

/B

Magnetic Field (T)

3.0 4.5

M

/B

Magnetic Field (T)

3.5 4.0 4.5

M

/B

Magnetic Field (T)

Mag

net

ic f

ield

|| a

Hydrogentated Deuterated

Mag

net

ic f

ield

|| c

(a) (d)(b)

(c)

6.4 6.8 7.20.0

0.5

1.0

1.5

2.0

2.5

J3

J4

J2

J5

-J (

K)

Distance between FeFe (Å)

J1(H

2O)

J1

J2J4

J5 J3

0 2 4 6 80

5

10

15

20

25

30

35

Mag

net

ic F

ield

(T

)

Temperature (K)0 2 4 6 8

0

5

10

15

20

25

30

35

Mag

net

ic F

ield

(T

)

Temperature (K)0 2 4 6 8

0

5

10

15

20

25

30

35

Mag

net

ic F

ield

(T

)

Temperature (K)A. Clune, et al., npj Quant. Mater. (2019); Ackermann, et al., New Journal of Physics (2013); W. Tian, et al., PRB (2018)

• previous studies only went to 15 T

• transition to fully polarized state at 30.3 T

• linked to J1

J1

J1

Developing the phase diagram (hydrogenated B ║ c)

(NH4)2FeCl5.H2O… the full view

A. Clune, et al., npj Quant. Mater. (2019); Ackermann, et al., New Journal of Physics (2013); W. Tian, et al., PRB (2018)

electric polarization across the magnetic quantum phase transition?

A

- +

- +

P

B

Pulsed fields = very low noise!

Pulse up to 65 T

electric polarization across the magnetic quantum phase transition

consequences of Type II multiferroic:

ferroelectricity derives from magnetic order

spin-lattice interactions in multiferroics

[(CH3)2NH2]Mn(HCOO)3 (NH4)2FeCl5∙H2O

U

tJ AFM

2

~

K. D. Hughey, PRB 96, 180305 (2017).

phonon mode links

ferroicities!

?

Spin-phonon coupling in Ruby?

NH4 and H2O

librations

evaluate coupling constants?

What we learned…• able to drive molecular multiferroics into the

fully saturated state at realizable fields

• generated a rich + complex B-T phase diagram

• opens door to exploring high field properties

A. Clune, et. al, npj Quant. Mater. (2019)

We thank

NSF and NHMFL for

support of this work!

(a) (d)(b)

(c)

6.4 6.8 7.20.0

0.5

1.0

1.5

2.0

2.5

J3

J4

J2

J5

-J (

K)

Distance between FeFe (Å)

J1(H

2O)