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1、,第二讲磁记录材料,History of magnetism,司南是我国春秋战国时代发明的一种最早的指示南北方向的指南器。中华民族很早就认识到了磁现象，古代中国在磁的发现、发明和应用上等许多方面都居于世界首位，可以说中国是磁的故乡。,物质的磁性来自构成物质的原子，原子的磁性又主要来自原子中的电子。原子中电子的磁性有两个来源：一个来源是电子本身具有自旋磁矩；另一个来源是电子绕原子核作轨道运动时产生轨道磁矩。,抗磁性顺磁性铁磁性反铁磁性亚铁磁性,生物磁现象生物磁现象 核磁共振层析成像 心磁图和脑磁图 鸽子回家和海龟回游 磁性细菌的磁导航,地球磁现象地球磁场的变化和应用 地球磁场的反向 地磁与大陆漂
2、移及海底扩张 地球磁场与极光 地球磁场的起源,宇宙磁现象太阳磁场与太阳黑子 阿尔法()磁谱仪空间探测“阿波罗”飞船测月磁 磁场与空间气象学 脉冲星与超强磁场,原子核与基本粒子磁现象电子磁距和中子磁距 核磁共振与物质结构研究 穆斯堡尔效应与磁结构研究 核磁致冷创造最低温度记录 核铁磁性和核反铁磁性,磁性无处不在,History of magnetic recording,Oberlin Smith diagram,1888,Valdemar Poulsen,1898,Fritz Pfleumer,1928,BASF magnetic tapefrom Ritter,1988,AEG Magnet
3、ophon,1935,The categories and structures of hard disk,Disc Drives Today Cover the Widest Range of Users and Systems Ever,Low-cost,high-capacity,disk drives are enabling new devices,resulting in rapid growth of the storage industry and the emergence of new industries.e.g.Apple iPod,PVRs,X-Box,automob
4、ile navigation systems,digital video cameras,etc.,Read/write heads,Applications in Data Storage,Writing HeadsHeads used for writing bits of information onto a spinning magnetic disk depend on phenomena A and B to produce and control strong magnetic fields.Reading HeadsReading heads depend on phenome
5、na A,B,and C,and are sensitive to the residual magnetic fields of magnetized storage media(D).Storage Media(e.g.,computer disks)Magnetic storage media are permanently magnetized in a direction(North or South)determined by the writing field.Storage media exploit phenomenon D.,Writing Heads and Readin
6、g Heads,FIGURE 1:A WRITING HEAD,FIGURE 2:WRITING DATA ON ASTORAGE MEDIUM.,FIGURE 3:READING DATA FROM ASTORAGE MEDIUM,FIGURE 4:INTEGRATED WRITE-READ HEAD,TGMR/GMR Reader Materials,Alternate Barrier TGMR(MgO)Improved amplitude,and lower RA Potential to extend TGMR reader to area density Current proble
7、m Maintaining soft magnetic property of free layer,while keeping high DR/R and low RA.CCP Design(current confined path)A discontinuous oxide buried in metalHigher DR/R and RA as compared to CPP Spin ValuePotential to use for area density of 400 600Gb/In2.Current problem Reducing variation of RA,and
8、DR/R,and increasing DR/R.CPP Spin Valve With Metal or Half Metal SpacerCould offer better reliability,and SNR at very high KTPI Potential to use for area density of 600Gb/In2 and behindCurrent problem Concept not proven,and processing half metals at temperature magnetic head can tolerate difficult,R
9、eader Development Approaches,Storage Media,The first PC hard disks typically held 16 sectors per track,20 concentric tracks Todays hard disks can have thousands of sectors in a single track,This illustration gives you some idea of just how small the flying height of a modern hard disk is,Overview of
10、 magnetic recording media,Before 1985:Fe2O3 medium,Ferrite ring head(10Mbin-2)1980:1st thin film read head,continuous magnetic thin film with high Hc,small(25%CGR);1990:1st MR read head,decreasing thickness and,in turn,the transition distance(80%CGR);1997:1st GMR read head(100%CGR);2000:1st AFM medi
11、um,increasing the effective volume.2006:1st TMR head for 80-100 Gbit in-2 perpendicular recording,The develop of the magnetic recording,Outline,Recording OverviewLongitudinal RecordingPerpendicular RecordingHeat Assisted Magnetic RecordingBit Patterned Media.,Magnetic Recording Traditional longitudi
12、nal recording is approaching to its limit(100 Gbit in-2 is achieved).(2)perpendicular recording offers about 610Gbit/in2,2008(3)the next big challenge is 1 Tbit in-2 for recording industry.The possible models:pattern media;high Ku media(HAMR);STT(Spin torque transfer)RAM.,Areal Density Growth,Single
13、 particle superparamagnetic limit(estimated),Charaps limit(broken),Late 1990s super paramagnetic limit demonstrated through modelingLongitudinal recording reaching areal density limits Longitudinal anti-ferromagnetic recording(AFC)Perpendicular expected to extend to 0.5-1 Tb/in2Additional innovation
14、s required at that pointheat-assisted recording(HAMR)bit patterned media(BPM)recording,Areal Density CAGR 40%Transfer Rate CAGR 20%,Perpendicular,HAMR,HAMR+BPM,Physical grain size below 10 nm,Magnetic Media Evolution,1955-1985:-Fe2O3 particles were dispersed in a polymer blinder and spin-coated on s
15、ubstrates of Al-Mg with an anodized aluminum oxide layer.Thin film disk technology started after 1985.,To preserve SNR,number of grains in a bit must be constant.SNRlog10(N)Therefore higher densities require smaller grains,The smaller bits have a higher probability of flipping and the data is unstab
16、le,High areal density means small volume,Super paramagnetic limit,Reasons to use PMR,Advantages of PA recording:a.high orientation ratiob.lower media noise(smaller)c.increase of signal and thermal stabilityd.writing field large,Application of the perpendicular media,2004年，东芝成为世界首个将垂直磁记录技术应用于商业硬盘的厂商。
17、垂直磁记录自1977年其原理提出之后，直到约30年后的2004年采用垂直磁记录方式的硬盘才首次亮相。日立公司表示，他们2005年4月实现230 Gbit/in2，2006年9月实现345 Gbit/in2，2008年08月04日他们创造了垂直磁记录密度的新纪录，达到了610Gbit/in2。但是由于目前垂直磁记录技术中使用的连续薄膜介质终将会达到一个密度极限，因此以后还会发展其他技术继续提高容量密度，例如离散磁道、热辅助记录等等。,Limits on conventional perpendicular recording,SmCo5,HAMA(Heat Assisted Magnetic R
18、ecording),Magnetic domains oriented in the direction of travel of the head.,Longitudinal Recording,Perpendicular Recording,Soft underlayer“mirrors”write head and makes it possible to write domains much closer together.,J.P.Wang,Nat.Mater.4,191(2005),New routine Tilted media,New routine Bit Patterned
19、 Media Lithography vs.Self Organization,Lithographically Defined,Major obstacle is finding low cost means of making media,Direct E-Beam Write or Di-Block Co-Polymer,Idea:Use Pattern Assisted Assembly to establish circumferential tracks on discs,FePt Self-Organizing Media,mm,ES,ECC and graded media,A
20、dvantages of ECC media:Lower switching field:enhance Writability Dynamical tilting reversal:eliminates Noise Higher Ku hard layer:enhance Thermal stability,R.H.Victora,IEEE Trans.Magn.41,537(2005);D.Suess,Appl.Phys.Lett.87,012504(2005);D.Suess,Appl.Phys.Lett.89,113105(2006).,软磁/硬磁复合介质,降低矫顽力，保持/提高热稳定性，解决了超高密度垂直磁记录介质的三难问题。,习题,1、谈谈对磁记录薄膜材料的认识。2、提高硬盘盘片的记录密度有哪些途径？3.为什么要用软磁硬磁交换耦合薄膜？,
