Electronic and magnetic properties of ycro 3 and yfeo 3 a first principles study
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Electronic and Magnetic Properties of YCrO 3 and YFeO 3 – 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 YFeO 3 YCrO 3.

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

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Electronic and magnetic properties of ycro 3 and yfeo 3 a first principles study

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

Overview of the talk

  • Introduction to multiferroics

  • Computational details

  • Results and Discussion

    • YFeO3

    • YCrO3


Introduction

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

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.


Different magnetic spin structures

Different magnetic spin structures

G-type AFM

C-type AFM

A-type AFM

FM


Yfeo 3

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


Comparison of total energies

Comparison of Total energies


Band structure and density of states dos of yfeo 3

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

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

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

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)


Ycro 3

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


Comparison of total energies1

Comparison of Total energies


G type antiferromagnetic ordering

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

Hubbard U = 1 (G-type)

Band Gap = 1.648 eV


Comparison of experimental and theoretical results

Comparison of experimental and theoretical results


Libra cluster

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

Acknowledgment

  • High Performance Computing Environment (HPCE), IIT Madras.

  • DBT for funding (CASTEP).

  • Mr. V. Ravichandran, HPCE

  • Mrs. P. Gayathri, HPCE

  • Mr. C. Ganeshraj


Thank you

Thank You


Ferromagnetic ordering

Ferromagnetic ordering

Band Gap = 0.759 eV


C type antiferromagnetic ordering

C-type antiferromagnetic ordering

Band Gap = 1.082 eV


A type antiferromagnetic ordering

A-type antiferromagnetic ordering


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