Magnetic properties of III MnAs diluted magnetic semiconductors

Magnetic properties of (III, Mn)As diluted magnetic semiconductors Katarzyna Kluczyk Supervisor: Dr. Shengqiang Zhou Institute of ion beam physic and material research, HZDR Dresden

Outline Introduction • Diluted magnetic semiconductors • Preparation of DMS • Origin of ferromagnetism • Electrically control the ferromagnetism in DMS HZDR project • Samples • First results Summary

Future of spintronics Spintronics: Electronics: • applications: diodes, transistors, detectors, lasers, solar cells • manipulate: charge of electrons • material: semiconductors + • applications: memories, higher speed, lower power, tunable , detectors and lasers • manipulate: spin of electrons • material: ferromagnetic Diluted magnetic semiconductors : charge and spin manipulation • storage and processing information at the same time • heterostructures with nonmagnetic semiconductors ( spin based optoelectronic, quantum computation)

Ohno, H. , Science. 281, 951 (1998). Diluted magnetic semiconductors ( DMS) • Aim: combine magnetic properties of ferromagnetics with electrical properties of the semiconductors • alloy between nonmagnetic semiconductor and magnetic element What we want: • no strong disturbed electric band structure of host semiconductor • could be doped to type p and n • Curie temperature above room temperature

Preparation of DMS Low temperature molecular beam epitaxy ( LT-MBE ): • kinetically suppressed formation of second phases ( low temperature) Ion beam implantation and annealing: • higher solubility limit in liquid phase of host semiconductor Substrate temperature (o. C) Main problems: low solubility of magnetic elements ( e. g. Mn ) compounds ( much below 0. 1% ) Magnetic effect proportional to magnetic element concentration Mn. As Precipitates 300 Metallic (Ga. Mn)As 200 Insulating (Ga. Mn)As Roughness Polycrystalline 100 0 0. 02 0. 04 0. 06 0. 08 Mn composition x H. Ohno , J. of Magnetism and Magnetic Materials 200 (1999)

• Mn ion substitute Ga, In • currier concentration = Mn concentration ~ 1020 (cm-2) • Exchange interaction between curries and localized spins • Curie temperature Tc 1: 90 -170 K for Ga 1 -x. Mnx. As x=5 -9% 46 K for In 1 -x. Mnx. As x=4 -5% Mn(Ga, In): acceptor ( provides hole) local spin moment Mn (I) : double donor ( provides 2 electrons) 1 S. Zhou et al. , Appl. Phys. Express 5 (2012) 093007 Crystal structure of (Ga, Mn)As Mn: [Ar] 3 d 54 s 2 Ga: [Ar] 3 d 104 s 2 p 1 In: [Kr]4 d 105 s 25 p 1 Wang H L, Chen L, Zhao J H. Sci China-Phys Mech Astron, 2013 Ga 1 -x. Mnx. As, In 1 -x. Mnx. As

Origin of ferromagnetism Hm =Σk. J(r-Rk)σSk n – carries concentration N – concentration of localized spins Paramagnetic Curie temperature ( a. u. ) • exchange interaction between carries and localized spins • curried mediated ferromagnetism RKKY theory RKKY interaction ferromagnetic n/N antiferromagnetic R. Galazka, Semimagnetic semicondiuctors, (1977)

Electric-field control of ferromagnetic properties Electric control of ferromegnetic phase a) Schematic view of the effect b) magnetization curves obtained through a measure of the Hall resistivity in (In, Mn)As at different gate voltages H. Ohno, Nature materials, vol. 9, 952 -54, 2010

Outline Introduction • Diluted magnetic semiconductors • Preparation of DMS • Origin of ferromagnetism • Selected electrical properties of DMS HZDR project • Samples • First results Summary

Samples Schematic view of samples Lattice constant equal lattice constant in In. P („ferro diods” on (In. Ga, Mn)As/In. P ) Implanted by Mn ions , dose φ = 1016 (cm-2), ion beam energy 90 ke. V Annealed with single laser pulse and energy density 0. 25, 0. 35, 0. 4 ( J/cm 2) Xe. Cl excimer laser ( Coherent COMPex. PRO 201, λ=398 nm, 30 ns , full width at half maximum )

Monte Carlo simulation of Mn distribution with program SRIM Rp – ion range of max concentration ΔRp – ion range straggling Rp =567Å ΔRp=294Å Rp =506Å ΔRp=274Å Rp =550Å ΔRp=283Å Deph (Å)

Magnetic moment measurements by SQUID magnetometer as a function of applied magnetic field in temperature 5 K

Magnetic moment as a function of temperature measured in magnetic field 20 Oe

Summary • Both Ga. As/In. Ga. As superlattice and In. Ga. As can be prepared to be DMS • Ion implantation and PLA: an effective method to synthesis DMS Directions for further research: • Measurements of magnetization response along perpendicular direction ( to investigate magnetic anisotropy ) • Measurements of samples annealed with different energy density (investigation of proper annealing conditions ) • Investigation of Tc dependence on In concentration • Measurements of magnetization dependence on temperature for In. Ga. As/Ga. As multilayer. Looking for two magnetic phases.

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