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Electronic and Magnetic Properties of YCrO 3 and YFeO 3 – A First Principles StudyPowerPoint Presentation

Electronic and Magnetic Properties of YCrO 3 and YFeO 3 – A First Principles Study

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### Electronic and Magnetic Properties of YCrO3 and YFeO3–A First Principles Study

Vidhya G Nair

Department of Physics

IIT Madras

HPC Symposium 2014 - April 25, 2014

Overview of the talk

- Introduction to multiferroics
- Computational details
- Results and Discussion
- YFeO3
- YCrO3

Introduction

Multiferroics more than one ferroic order coexist and

are coupled

(magnetic, electric or elastic)

(usually refers specifically to)

- Rare earth chromites and ferrites shows
multiferroic behavior.

- YCrO3 and YFeO3
- orthorhombic structure
- canted antiferromagnet
- Neel temperature (TN) of ~140 K and ~655 K [1, 2]

Daniel Khomskii, Physics2, 20 (2009)

- [1] J. R. Sahuet al., J. Mater. Chem., 17, (2007) 42.
- [2] M. Shang et al., Appl. Phys. Lett., 102, (2013) 062903.

Computational details

- First principles calculation of the electronic and magnetic properties of YCrO3 and YFeO3 is performed within generalized gradient approximation.
- The calculations are executed by employing the Cambridge Serial Total Energy Package (CASTEP) code based on density functional theory.
- The calculations were performed by the ultrasoft pseudopotential method with plane-wave basis which describes the interaction of electrons with ion cores.
- Structural optimizations are carried out for both samples with all possible magnetic structures.

YFeO3

Space group - Pnma

Lattice parameter

a = 5.7909 Å b = 7.7354 Å c = 5.4407 Å

α = β = γ = 90o

G-type AFM

Band structure and Density of states (DOS) of YFeO3

Band structure and density of states of G-type antiferromagnet YFeO3 shows the insulating behavior.

Effect of Hubbard parameter (U)

Density of states without U parameter.

Density of states with U = 5 eV.

Effect of Hubbard U parameter for G-AFM

Density of states of G-type AFM

with U = 1 to 5 eV.

Partial density of states contribution

to total DOS

Estimation of magnetic – ordering temperature

- To estimate the magnetic-ordering temperature for YFeO3, the Heisenberg
exchange constants corresponding to the nearest-neighbor magnetic

couplings for the magnetic configuration is determined.

- The calculated energies are mapped onto a simple Heisenberg model,
- From the coupling constants, the magnetic-ordering temperature is calculated
using the mean-field approximation.

- The magnetic transition temperature for G-type magnetic structure is
calculated to be 700 K which is close to that of the experimental value TN = 655 K.

Magnetic moment Fe3+ : 3.82 μB (5 μB)

YCrO3

Space group - Pnma

Lattice parameter

a = 5.5157 Å b = 7.5301 Å c = 5.2409 Å

α = β = γ = 90o

G-type AFM

G-type Antiferromagnetic ordering

Band Gap = 1.435 eV

Magnetic moment Cr3+ : 2.98 μB (3 μB)

- The magnetic transition temperature for G-type magnetic structure is
calculated to be 137 K (TN = 140 K).

Hubbard U = 1 (G-type)

Band Gap = 1.648 eV

LIBRA cluster

- We are extensively using LIBRA cluster for running our programs.
- The total time used for each calculation depends on the sample.
- For the present samples, the run time for each structural optimization is approximately one week, if 4 processors are used for calculation.

Acknowledgment

- High Performance Computing Environment (HPCE), IIT Madras.
- DBT for funding (CASTEP).
- Mr. V. Ravichandran, HPCE
- Mrs. P. Gayathri, HPCE
- Mr. C. Ganeshraj

Ferromagnetic ordering

Band Gap = 0.759 eV

C-type antiferromagnetic ordering

Band Gap = 1.082 eV

A-type antiferromagnetic ordering

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