Magnetic and structural properties of MnRh thin films

Anurag Chaturvedi,Takao Suzuki

doi:10.1063/1.4944405

Abstract

A systematic study of magnetic and structural properties of MnRh thin films fabricated onto MgO substrates and amorphous SiO2 has been conducted. All the MnRh thin films thus fabricated are found to be of the CsCl type structure, and exhibit the ferromagnetism at room temperature. The coercivity of about 1.1 kOe was observed at 5 K for films grown onto SiO2 substrates, while coercivity measured at 300 K in all the films were less than 200 Oe. The temperature dependence of magnetization shows thermal hysteresis for all the samples ranging from 150 K to 250 K that varies with the substrates used. The maximum of exchange bias field of 270 Oe and unidirectional magnetic anisotropy constant of 0.35 erg/cm2 at 5K was observed for films grown onto SiO2 substrates better than that observed for the films grown onto MgO substrates. This enhanced exchange bias and unidirectional magnetic anisotropy constant in film grown onto SiO2 is attributed to the strong lattice distortion in such a case.

Highlights

Manganese-based alloys are the attractive classes of materials for high magnetic anisotropy of the order of 1x107 erg/cc for both ferromagnetic and antiferromagnetic phases, attractive permanent magnets (MnBi, MnAl) and /or for giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) devices (MnIr, MnPd, MnNi).[1,2,3,4] Bulk MnRh is reported to be antiferromagnetic at room temperature, the Néel point of which is 1330 K.5 the magnetic anisotropy constant of MnRh is reported to be -1.9x107 erg/cc, highest among the anti-ferromagnetic Mn-X compounds except for MnIr (2x108 erg/cc).[6]
The maximum of exchange bias field of 270 Oe and unidirectional magnetic anisotropy constant of 0.35 erg/cm[2] at 5K was observed for films grown onto SiO2 substrates better than that observed for the films grown onto MgO substrates
The temperature dependence of magnetization, together with the result of high resolution TEM observations suggested that the exchange bias effect is due to the coupling between the ferro- and antiferro-magnetic phases resulted from the compositional fluctuation within a MnRh grain of the CsCl structure

Summary

INTRODUCTION

Manganese-based alloys are the attractive classes of materials for high magnetic anisotropy of the order of 1x107 erg/cc for both ferromagnetic and antiferromagnetic phases, attractive permanent magnets (MnBi, MnAl) and /or for giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) devices (MnIr, MnPd, MnNi).[1,2,3,4] Bulk MnRh is reported to be antiferromagnetic at room temperature, the Néel point of which is 1330 K.5 the magnetic anisotropy constant of MnRh (bulk) is reported to be -1.9x107 erg/cc, highest among the anti-ferromagnetic Mn-X compounds except for MnIr (2x108 erg/cc).[6]. The magnetic anisotropy constant of MnRh (bulk) is reported to be -1.9x107 erg/cc, highest among the anti-ferromagnetic Mn-X compounds except for MnIr (2x108 erg/cc).[6] Previous works showed that MnRh thin films exhibited the ferromagnetic behaviors.[7] A recent work discussed the exchange bias mechanism in MnRh thin films fabricated onto amorphous SiO2 substrates at an ambient temperature.[8] The temperature dependence of magnetization, together with the result of high resolution TEM observations suggested that the exchange bias effect is due to the coupling between the ferro- and antiferro-magnetic phases resulted from the compositional fluctuation within a MnRh grain of the CsCl structure. Since the magnetic anisotropy of both the ferro- and antiferro-magnetic phases of MnRh is expected to be strongly dependent on the c/a ratio, where a and c are the lattice parameters, as found in other Mn-X systems such as MnIr, MnPd, the present has been motivated to explore the possibility to enhance the exchange bias effect by choosing single crystal substrates, so as to change the lattice constants of the films fabricated

EXPERIMENTAL

RESULTS AND DISCUSSION

SUMMARY